D-Link DES-3326 User Manual

Download

DES-3326

24-Port Fast Ethernet

Plus 2-Port Gigabit Module

Layer 3 Switch

Second Edition (July 2002)

651ES3326025

Printed In Taiwan

RECYCLABLE

User’s Guide

Wichtige Sicherheitshinweise

1. Bitte lesen Sie sich diese Hinweise sorgfältig durch.

2. Heben Sie diese Anleitung für den spätern Gebrauch auf.

3. Vor jedem Reinigen ist das Gerät vom Stromnetz zu trennen. Vervenden Sie keine Flüssig- oder Aerosolreiniger. Am besten dient ein angefeuchtetes Tuch zur Reinigung.

4. Um eine Beschädigung des Gerätes zu vermeiden sollten Sie nur Zubehörteile verwenden, die vom Hersteller zugelassen sind.

5. Das Gerät is vor Feuchtigkeit zu schützen.

6. Bei der Aufstellung des Gerätes ist auf sichern Stand zu achten. Ein Kippen oder Fallen könnte Verletzungen hervorrufen. Verwenden Sie nur sichere Standorte und beachten Sie die Aufstellhinweise des Herstellers.

7. Die Belüftungsöffnungen dienen zur Luftzirkulation die das Gerät vor Überhitzung schützt. Sorgen Sie dafür, daß diese Öffnungen nicht abgedeckt werden.

8. Beachten Sie beim Anschluß an das Stromnetz die Anschlußwerte.

9. Die Netzanschlußsteckdose muß aus Gründen der elektrischen Sicherheit einen Schutzleiterkontakt haben.

10. Verlegen Sie die Netzanschlußleitung so, daß niemand darüber fallen kann. Es sollete auch nichts auf der Leitung abgestellt werden.

11. Alle Hinweise und Warnungen die sich am Geräten befinden sind zu beachten.

12. Wird das Gerät über einen längeren Zeitraum nicht benutzt, sollten Sie es vom Stromnetz trennen. Somit wird im Falle einer Überspannung eine Beschädigung vermieden.

13. Durch die Lüftungsöffnungen dürfen niemals Gegenstände oder Flüssigkeiten in das Gerät gelangen. Dies könnte einen Brand bzw. Elektrischen Schlag auslösen.

14. Öffnen Sie niemals das Gerät. Das Gerät darf aus Gründen der elektrischen Sicherheit nur von authorisiertem Servicepersonal geöffnet werden.

15. Wenn folgende Situationen auftreten ist das Gerät vom Stromnetz zu trennen und von einer qualifizierten Servicestelle zu überprüfen: a – Netzkabel oder Netzstecker sint beschädigt. b – Flüssigkeit ist in das Gerät eingedrungen. c – Das Gerät war Feuchtigkeit ausgesetzt. d – Wenn das Gerät nicht der Bedienungsanleitung ensprechend funktioniert oder Sie mit Hilfe dieser Anleitung keine Verbesserung erzielen. e – Das Gerät ist gefallen und/oder das Gehäuse ist beschädigt. f – Wenn das Gerät deutliche Anzeichen eines Defektes aufweist.

16. Bei Reparaturen dürfen nur Orginalersatzteile bzw. den Orginalteilen entsprechende Teile verwendet werden. Der Einsatz von ungeeigneten Ersatzteilen kann eine weitere Beschädigung hervorrufen.

17. Wenden Sie sich mit allen Fragen die Service und Repartur betreffen an Ihren Servicepartner. Somit stellen Sie die Betriebssicherheit des Gerätes sicher.

18. Zum Netzanschluß dieses Gerätes ist eine geprüfte Leitung zu verwenden, Für einen Nennstrom bis 6A und einem Gerätegewicht grőßer 3kg ist eine Leitung nicht leichter als H05VV-F, 3G, 0.75mm2 einzusetzen.

WARRANTIES EXCLUSIVE

IF THE D-LINK PRODUCT DOES NOT OPERATE AS WARRANTED ABOVE, THE CUSTOMER'S SOLE REMEDY SHALL BE, AT D-LINK'S OPTION, REPAIR OR REPLACEMENT. THE FOREGOING WARRANTIES AND REMEDIES ARE EXCLUSIVE AND ARE IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, EITHER IN FACT OR BY OPERATION OF LAW, STATUTORY OR OTHERWISE, INCLUDING WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. D-LINK NEITHER ASSUMES NOR AUTHORIZES ANY OTHER PERSON TO ASSUME FOR IT ANY OTHER LIABILITY IN CONNECTION WITH THE SALE, INSTALLATION MAINTENANCE OR USE OF D-LINK'S PRODUCTS D-LINK SHALL NOT BE LIABLE UNDER THIS WARRANTY IF ITS TESTING AND EXAMINATION DISCLOSE THAT THE ALLEGED DEFECT IN THE PRODUCT DOES NOT EXIST OR WAS CAUSED BY THE CUSTOMER'S OR ANY THIRD PERSON'S MISUSE, NEGLECT, IMPROPER INSTALLATION OR TESTING, UNAUTHORIZED ATTEMPTS TO REPAIR, OR ANY OTHER CAUSE BEYOND THE RANGE OF THE INTENDED USE, OR BY ACCIDENT, FIRE, LIGHTNING OR OTHER HAZARD.

LIMITATION OF LIABILITY

IN NO EVENT WILL D-LINK BE LIABLE FOR ANY DAMAGES, INCLUDING LOSS OF DATA, LOSS OF PROFITS, COST OF COVER OR OTHER INCIDENTAL, CONSEQUENTIAL OR INDIRECT DAMAGES ARISING OUT THE INSTALLATION, MAINTENANCE, USE, PERFORMANCE, FAILURE OR INTERRUPTION OF A D- LINK PRODUCT, HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY. THIS LIMITATION WILL APPLY EVEN IF D-LINK HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. IF YOU PURCHASED A D-LINK PRODUCT IN THE UNITED STATES, SOME STATES DO NOT ALLOW THE LIMITATION OR EXCLUSION OF LIABILITY FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES, SO THE ABOVE LIMITATION MAY NOT APPLY TO YOU.

Limited Warranty

Hardware:

D-Link warrants each of its hardware products to be free from defects in workmanship and materials under normal use and service for a period commencing on the date of purchase from D-Link or its Authorized Reseller and extending for the length of time stipulated by the Authorized Reseller or D-Link Branch Office nearest to the place of purchase.

This Warranty applies on the condition that the product Registration Card is filled out and returned to a D-Link office within ninety (90) days of purchase. A list of D-Link offices is provided at the back of this manual, together with a copy of the Registration Card.

If the product proves defective within the applicable warranty period, D-Link will provide repair or replacement of the product. D-Link shall have the sole discretion whether to repair or replace, and replacement product may be new or reconditioned. Replacement product shall be of equivalent or better specifications, relative to the defective product, but need not be identical. Any product or part repaired by D-Link pursuant to this warranty shall have a warranty period of not less than 90 days, from date of such repair, irrespective of any earlier expiration of original warranty period. When D-Link provides replacement, then the defective product becomes the property of D-Link.

Warranty service may be obtained by contacting a D-Link office within the applicable warranty period, and requesting a Return Material Authorization (RMA) number. If a Registration Card for the product in question has not been returned to D-Link, then a proof of purchase (such as a copy of the dated purchase invoice) must be provided. If Purchaser's circumstances require special handling of warranty correction, then at the time of requesting RMA number, Purchaser may also propose special procedure as may be suitable to the case.

After an RMA number is issued, the defective product must be packaged securely in the original or other suitable shipping package to ensure that it will not be damaged in transit, and the RMA number must be prominently marked on the outside of the package. The package must be mailed or otherwise shipped to D-Link with all costs of mailing/shipping/insurance prepaid. D-Link shall never be responsible for any software, firmware, information, or memory data of Purchaser contained in, stored on, or integrated with any product returned to D-Link pursuant to this warranty.

Any package returned to D-Link without an RMA number will be rejected and shipped back to Purchaser at Purchaser's expense, and D-Link reserves the right in such a case to levy a reasonable handling charge in addition mailing or shipping costs.

Software:

Warranty service for software products may be obtained by contacting a D-Link office within the applicable warranty period. A list of D-Link offices is provided at the back of this manual, together with a copy of the Registration Card. If a Registration Card for the product in question has not been returned to a D-Link office, then a proof of purchase (such as a copy of the dated purchase invoice) must be provided when requesting warranty service. The term "purchase" in this software warranty refers to the purchase transaction and resulting license to use such software.

D-Link warrants that its software products will perform in substantial conformance with the applicable product documentation provided by D-Link with such software product, for a period of ninety (90) days from the date of purchase from D-Link or its Authorized Reseller. D-Link warrants the magnetic media, on which D-Link provides its software product, against failure during the same warranty period. This warranty applies to purchased software, and to replacement software provided by D-Link pursuant to this warranty, but shall not apply to any update or replacement which may be provided for download via the Internet, or to any update which may otherwise be provided free of charge.

D-Link's sole obligation under this software warranty shall be to replace any defective software product with product which substantially conforms to D-Link's applicable product documentation. Purchaser assumes responsibility for the selection of appropriate application and system/platform software and associated reference materials. D-Link makes no warranty that its software products will work in combination with any hardware, or any application or system/platform software product provided by any third party, excepting only such products as are expressly represented, in D-Link's applicable product documentation as being compatible. D-Link's obligation under this warranty shall be a reasonable effort to provide compatibility, but D-Link shall have no obligation to provide compatibility when there is fault in the third-party hardware or software. D-Link makes no warranty that operation of its software products will be uninterrupted or absolutely error-free, and no warranty that all defects in the software product, within or without the scope of D-Link's applicable product documentation, will be corrected.

D-Link Offices for Registration and Warranty Service

The product's Registration Card, provided at the back of this manual, must be sent to a D-Link office. To obtain an RMA number for warranty service as to a hardware product, or to obtain warranty service as to a software product, contact the D-Link office nearest you. An address/telephone/fax/e-mail/Web site list of D-Link offices is provided in the back of this manual.

Trademarks

Copyright 2002 D-Link Corporation. Contents subject to change without prior notice. D-Link is a registered trademark of D-Link Corporation/D-Link Systems, Inc. All other trademarks belong to their respective proprietors.

No part of this publication may be reproduced in any form or by any means or used to make any derivative such as translation, transformation, or adaptation without permission from D-Link Corporation/D-Link Systems Inc., as stipulated by the United States Copyright Act of 1976.

FCC Warning

This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with this user’s guide, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense.

CE Mark Warning

This is a Class A product. In a domestic environment, this product may cause radio interference in which case the user may be required to take adequate measures.

VCCI Warning

BSMI Warning

Table of Contents

Introduction .......................................................................................................................................10

Layer 3 Switching ............................................................................................................................10

The Functions of a Layer 3 Switch.................................................................................................11

Features ..........................................................................................................................................11

Ports .............................................................................................................................................11

Performance Features......................................................................................................................11

Layer 2 Features ...........................................................................................................................11

Layer 3 Switch Features................................................................................................................12

Traffic Classification and Prioritization ..........................................................................................13

Management .................................................................................................................................13

Optional Redundant Power Supply................................................................................................14

Fast Ethernet Technology ................................................................................................................14

Gigabit Ethernet Technology............................................................................................................14

Unpacking and Setup.........................................................................................................................15

Unpacking .......................................................................................................................................15

Installation ......................................................................................................................................15

Desktop or Shelf Installation .........................................................................................................15

Rack Installation...........................................................................................................................16

Power on..........................................................................................................................................17

Power Failure ................................................................................................................................17

Identifying External Components .......................................................................................................18

Front Panel......................................................................................................................................18

Rear Panel .......................................................................................................................................18

Side Panels ......................................................................................................................................19

Optional Plug-in Modules ................................................................................................................19

1000BASE-T Module.....................................................................................................................19

1000BASE-SX Fiber Module .........................................................................................................20

1000BASE-LX Fiber Module..........................................................................................................20

GBIC Two-Port Module..................................................................................................................21

LED Indicators ................................................................................................................................21

Connecting The Switch.......................................................................................................................22

Switch to End Node .........................................................................................................................22

Switch to Hub or Switch ..................................................................................................................22

10BASE-T Device ..........................................................................................................................23

100BASE-TX Device......................................................................................................................23

Switch Management and Operating Concepts ....................................................................................24

Local Console Management .............................................................................................................24

Diagnostic (console) port (RS-232 DCE).........................................................................................24

IP Addresses and SNMP Community Names ....................................................................................25

Traps...............................................................................................................................................26

SNMP ..............................................................................................................................................27

MIBs................................................................................................................................................28

Packet Forwarding ...........................................................................................................................28

Filtering...........................................................................................................................................29

Spanning Tree .................................................................................................................................30

Link Aggregation..............................................................................................................................35

VLANs .............................................................................................................................................37

IP Addresses ....................................................................................................................................41

vii

Internet Protocols ............................................................................................................................46

Packet Headers................................................................................................................................50

The Domain Name System ...............................................................................................................54

DHCP Servers ..................................................................................................................................55

IP Routing .......................................................................................................................................55

ARP .................................................................................................................................................57

Multicasting ....................................................................................................................................57

Multicast Routing Protocols .............................................................................................................62

Routing Protocols ............................................................................................................................62

Configuring the Switch Using the Console Interface ...........................................................................87

Saving Changes..................................................................................................................................93

Advanced Setup.............................................................................................................................112

Layer 3 IP Networking....................................................................................................................121

Multicasting ..................................................................................................................................133

Port Mirroring................................................................................................................................142

Priority ..........................................................................................................................................144

Filtering.........................................................................................................................................146

Forwarding ....................................................................................................................................148

Spanning Tree ...............................................................................................................................151

Link Aggregation............................................................................................................................154

Spanning Tree ...............................................................................................................................156

Utilities..........................................................................................................................................159

Network Monitoring .......................................................................................................................167

Load Factory Defaults....................................................................................................................182

Web-Based Network Management ....................................................................................................185

Introduction ..................................................................................................................................185

Before You Start ............................................................................................................................185

General Deployment Strategy......................................................................................................185

VLAN Layout ...............................................................................................................................186

Assigning IP Network Addresses and Subnet Masks to VLANs.....................................................186

Defining Static Routes.................................................................................................................187

Getting Started ..............................................................................................................................187

Management..................................................................................................................................187

Configuring the Switch ..................................................................................................................187

User Accounts Management........................................................................................................187

Saving Changes .............................................................................................................................189

Reboot and Load Factory Defaults .................................................................................................189

USING WEB-BASED MANAGEMENT .............................................................................................190

CONFIGURING AND MONITORING................................................................................................193

Advanced Setup.............................................................................................................................208

Layer 3 IP Networking....................................................................................................................215

Multicasting ..................................................................................................................................223

Port Mirroring................................................................................................................................231

Priority ..........................................................................................................................................233

Filtering.........................................................................................................................................234

Spanning Tree ...............................................................................................................................238

Link Aggregation............................................................................................................................241

Utilities..........................................................................................................................................242

Network Monitoring .......................................................................................................................247

Technical Specifications ...................................................................................................................262

Sample Configuration File ................................................................................................................264

viii

Runtime Switching Software Default Settings...................................................................................266

Understanding and Troubleshooting the Spanning Tree Protocol......................................................267

Blocking State.............................................................................................................................267

Listening State ............................................................................................................................268

Learning State.............................................................................................................................269

Forwarding State.........................................................................................................................270

Disabled State.............................................................................................................................271

Troubleshooting STP......................................................................................................................272

Spanning Tree Protocol Failure ...................................................................................................272

Full/Half Duplex Mismatch.........................................................................................................273

Unidirectional Link .....................................................................................................................274

Packet Corruption .......................................................................................................................275

Resource Errors ..........................................................................................................................275

Identifying a Data Loop ...............................................................................................................275

Avoiding Trouble .........................................................................................................................275

Brief Review of Bitwise Logical Operations........................................................................................279

Index................................................................................................................................................280

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

INTRODUCTION

This section describes the Layer 3 functionality and Layer 2 and Layer 3 features of the DES-3326. Some background information about Ethernet/Fast Ethernet, Gigabit Ethernet, and switching technology is presented. This is intended for readers who may not be familiar with the concepts of layered switching and routing but is not intended to be a complete or in-depth discussion.

Layer 3 Switching

Layer 3 switching is the integration of two proven technologies: switching and routing. In fact, Layer 3 switches are running the same routing routines and protocols as traditional routers. The main difference between traditional routing and Layer 3 switching is the addition of a group of Layer 2 switching domains and the execution of routing routines for most packets via an ASIC – in hardware instead of software.

Where a traditional router would have one, or at best a few, Fast Ethernet ports, the DES-3326 Layer 3 switch has 24 Fast Ethernet ports and optionally, 2 Gigabit Ethernet ports. Where a traditional router would have one or two high-speed serial WAN connections, the DES-3326 relies upon a Fast Ethernet port to connect to a separate device, which in turn, connects the network to a WAN or the Internet.

The DES-3326 can be thought of as 24 Fast Ethernet Layer 2 switching domains with a wire-speed router between each domain. It can be deployed in a network between a traditional router and the intranetwork. The traditional router and its associated WAN interface would then handle routing between the intranetwork and the WAN (the Internet, for example) while the Layer 3 switch would handle routing within the LAN (between the Fast Ethernet Layer 2 domains). Any installed Layer 2 switches, and indeed the entire subnetting scheme, would remain in place.

The DES-3326 can also replace key traditional routers for data centers and server farms, routing between these locations and the rest of the network, and providing 24 ports of Layer 2 switching performance combined with wire-speed routing.

Backbone routers can also be replaced with DES-3326 and a series of DES-3326 could be linked via the optional Gigabit Ethernet ports. Routers that service WAN connections would remain in place, but would now be removed from the backbone and connected to the DES-3326 via an Ethernet/Fast Ethernet port. The backbone itself could be migrated to Gigabit Ethernet, or faster technologies as they become available.

The DES-3326 accomplishes two objectives. First as a tool to provide high-performance access to enterprise data servers and infrastructure, and second, to enhance the performance of network equipment already installed. Many network segments display poor performance, but the Ethernet wire is only carrying a fraction of its total traffic capacity. The problem is not the network, but the ability of the connected devices utilize the full capacity of the network. The DES-3326 can eliminate network bottlenecks to high-traffic areas, and improve the utilization of the network’s installed bandwidth.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The Functions of a Layer 3 Switch

Traditional routers, once the core components of large networks, became an obstacle to the migration toward next-generation networks. Attempts to make software-based routers forward packets more quickly were inadequate.

A layer 3 switch does everything to a packet that a traditional router does:

• Determines forwarding path based on Layer 3 information

• Validates the integrity of the Layer 3 header via checksum

• Verifies packet expiration and updates accordingly

• Processes and responds to any optional information

• Updates forwarding statistics in the Management Information Base

A Layer 3 switch can be placed anywhere within a network core or backbone, easily and cost-effectively replacing the traditional collapsed backbone router. The DES-3326 Layer 3 switch communicates with a WAN router using a standard Ethernet/Fast Ethernet port. Multiple DES-3326 switches can be linked via the optional, 2-port Gigabit Ethernet module.

Features

The DES-3326 Switch was designed for easy installation and high performance in an environment where traffic on the network and the number of users increase continuously.

Switch features include:

Ports

• 24 high-performance NWay ports all operating at 10/100 Mbps for connecting to end stations, servers and hubs (23 MDI-X 10/100 Ethernet UTP ports and one MDI-II/MDI-X port. The MDIII/MDI-X port can be switched between the two modes from the front panel.)

• All ports can auto-negotiate (NWay) between 10Mbps/ 100Mbps, half-duplex or full duplex and flow control for half-duplex ports.

• One front panel slide-in module interface for a 2-port 1000BASE-SX, 1000BASE-LX, 1000BASET, or GBIC Gigabit Ethernet module.

• RS-232 DCE Diagnostic port (console port) for setting up and managing the Switch via a connection to a console terminal or PC using a terminal emulation program.

Performance Features

Layer 2 Features

• 8.8 Gbps switching fabric capacity

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Store and forward switching scheme.

• Full and half-duplex for both 10Mbps and 100Mbps connections. The front-port Gigabit Ethernet

module operates at full duplex only. Full duplex allows the switch port to simultaneously transmit and receive data, and only works with connections to full-duplex capable end stations and switches. Connections to hubs must take place at half-duplex.

• Supports IEEE 802.3x flow control for full-duplex mode ports.

• Supports Back-pressure flow control for half-duplex mode ports.

• Auto-polarity detection and correction of incorrect polarity on the transmit and receive twisted-

pair at each port.

• IEEE 802.3z compliant for all Gigabit ports (optional module).

• IEEE 802.3x compliant Flow Control support for all Gigabit ports (optional module).

• IEEE 802.3ab compliant for 1000BASE-T (Copper) Gigabit ports (optional module).

• Data forwarding rate 14,880 pps per port at 100% of wire-speed for 10Mbps speed.

• Data forwarding rate 148,800 pps per port at 100% of wire-speed for 100Mbps speed.

• Data filtering rate eliminates all error packets, runts, etc. at 14,880 pps per port at 100% of wire-

speed for 10Mbps speed.

• Data filtering rate eliminates all error packets, runts, etc. at 148,800 pps per port at 100% of wire-speed for 100Mbps speed.

• 8K active MAC address entry table per device with automatic learning and aging (10 to 9999 seconds).

• 16 MB packet buffer per device.

• Broadcast and Multicast storm filtering.

• Supports Port Mirroring.

• Supports Port Trunking – up to six trunk groups (each consisting of up to eight ports) may be set

up.

• 802.1D Spanning Tree support.

• 802.1Q Tagged VLAN support – up to 63 User-defined VLANs per device (one VLAN is reserved

for internal use).

• GVRP – (GARP VLAN Registration Protocol) support for dynamic VLAN registration.

• 802.1p Priority support with 4 priority queues.

• IGMP Snooping support.

• Layer 2 Multicast support – GMRP (GARP Multicast Registration Protocol).

Layer 3 Switch Features

• Wire speed IP forwarding.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Hardware-based Layer 3 IP switching.

• IP packet forwarding rate of 6.6 Mpps.

• 2K active IP address entry table per device.

• Supports RIP – (Routing Information Protocol) version I and II.

• Supports OSPF − (Open Shortest Path First)

• Supports MD5 and Password OSPF Packet Authentication

• Supports IP version 4.

• IGMP version 1 and 2 support (RFC 1112 and RFC 2236).

• Supports PIM Dense Mode.

• Supports DVMRP.

• Supports IP multi-netting.

• Supports IP packet de-fragmentation.

• Supports Path MTU discovery.

• Supports 802.1D frame support.

Traffic Classification and Prioritization

• Based on 802.1p priority bits

• 4 priority queues

Management

• RS-232 console port for out-of-band network management via a console terminal or PC.

• Spanning Tree Algorithm Protocol for creation of alternative backup paths and prevention of

network loops.

• SNMP v.1 Agent.

• Fully configurable either in-band or out-of-band control via SNMP based software.

• Flash memory for software upgrades. This can be done in-band via TFTP or out-of-band via the

console.

• Built-in SNMP management:

 Bridge MIB (RFC 1493)

 MIB-II (RFC 1213)

 Mini-RMON MIB (RFC 1757) – 4 groups

 CIDR MIB (RFC 2096), except IP Forwarding Table.

 802.1p MIB (RFC 2674).

 RIP MIB v2 (RFC 1724).

• Supports Web-based management.

• TFTP support.

• BOOTP support.

• BOOTP Relay Agent.

• IP filtering on the management interface.

• DHCP Client support.

• DHCP Relay Agent.

• DNS Relay Agent.

• Password enabled.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Optional Redundant Power Supply

The DES-3326 24+2 Fast Ethernet Layer 3 Switch supports the optional DPS-1000 (Redundant Power Supply) to provide automatic power supply monitoring and switchover to a redundant power supply (located in the chassis of the DPS-1000) in case of a failure in the DES-3326’s internal power supply.

Fast Ethernet Technology

100Mbps Fast Ethernet (or 100BASE-T) is a standard specified by the IEEE 802.3 LAN committee. It is an extension of the 10Mbps Ethernet standard with the ability to transmit and receive data at 100Mbps, while maintaining the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Ethernet protocol.

Gigabit Ethernet Technology

Gigabit Ethernet is an extension of IEEE 802.3 Ethernet utilizing the same packet structure, format, and support for CSMA/CD protocol, full duplex, flow control, and management objects, but with a tenfold increase in theoretical throughput over 100Mbps Fast Ethernet and a one hundred-fold increase over 10Mbps Ethernet. Since it is compatible with all 10Mbps and 100Mbps Ethernet environments, Gigabit Ethernet provides a straightforward upgrade without wasting a company’s existing investment in hardware, software, and trained personnel.

Gigabit Ethernet enables fast optical fiber connections and Unshielded Twisted Pair connections to support video conferencing, complex imaging, and similar data-intensive applications. Likewise, since data transfers occur 10 times faster than Fast Ethernet, servers outfitted with Gigabit Ethernet NIC’s are able to perform 10 times the number of operations in the same amount of time.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

UNPACKING AND SETUP

This chapter provides unpacking and setup information for the Switch.

Unpacking

Open the shipping carton of the Switch and carefully unpack its contents. The carton should contain the following items:

♦ One DES-3326 24-port Fast Ethernet Layer 3 Switch

♦ Mounting kit: 2 mounting brackets and screws

♦ Four rubber feet with adhesive backing

♦ One AC power cord

♦ This User’s Guide with Registration Card

If any item is found missing or damaged, please contact your local D-Link reseller for replacement.

Installation

Use the following guidelines when choosing a place to install the Switch:

♦ The surface must support at least 3 kg.

♦ The power outlet should be within 1.82 meters (6 feet) of the device.

♦ Visually inspect the power cord and see that it is secured to the AC power connector.

♦ Make sure that there is proper heat dissipation from and adequate ventilation around the switch.

Do not place heavy objects on the switch.

Desktop or Shelf Installation

When installing the Switch on a desktop or shelf, the rubber feet included with the device should first be attached. Attach these cushioning feet on the bottom at each corner of the device. Allow adequate space for ventilation between the device and the objects around it.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 2-1. Installing rubber feet for desktop installation

Rack Installation

The DES-3326 can be mounted in an EIA standard-sized, 19-inch rack, which can be placed in a wiring closet with other equipment. To install, attach the mounting brackets on the switch’s side panels (one on each side) and secure them with the screws provided.

Figure 2- 2A. Attaching the mounting brackets to the switch

Then, use the screws provided with the equipment rack to mount the switch on the rack.

Figure 2-2B. Installing the switch on an equipment rack

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Power on

The DES-3326 switch can be used with AC power supply 100-240 VAC, 50 - 60 Hz. The power switch is located at the rear of the unit adjacent to the AC power connector and the system fan. The switch’s power supply will adjust to the local power source automatically and may be turned on without having any or all LAN segment cables connected.

After the power switch is turned on, the LED indicators should respond as follows:

♦ All LED indicators will momentarily blink. This blinking of the LED indicators represents a reset

of the system.

♦ The power LED indicator will blink while the Switch loads onboard software and performs a self-

test. After approximately 20 seconds, the LED will light again to indicate the switch is in a ready state.

♦ The console LED indicator will remain ON if there is a connection at the RS-232 port, otherwise

this LED indicator is OFF.

♦ The 100M LED indicator may remain ON or OFF depending on the transmission speed.

Power Failure

As a precaution in the event of a power failure, unplug the switch. When power is resumed, plug the switch back in.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

IDENTIFYING EXTERNAL COMPONENTS

This chapter describes the front panel, rear panel, optional plug-in modules, and LED indicators of the DES-3326.

Front Panel

The front panel of the Switch consists of LED indicators, an RS-232 communication port, a slide-in module slot, one switched MDI-X/MDI-II uplink port, and 23 (10/100 Mbps) Ethernet/Fast Ethernet ports.

Figure 3-1. Front panel view of the Switch

♦ Comprehensive LED indicators display the status of the switch and the network (see the LED

Indicators section below).

♦ An RS-232 DCE console port for setting up and managing the switch via a connection to a

console terminal or PC using a terminal emulation program.

♦ A front-panel slide-in module slot for Gigabit Ethernet ports can accommodate a 2-port

1000BASE-T Gigabit Ethernet module, a 2-port 1000BASE-SX Gigabit Ethernet module, a 2-port 1000BASE-LX Gigabit Ethernet module, or a 2-port GBIC-based Gigabit Ethernet module.

♦ One switched MDI-X/MDI-II Uplink port that can be used to connect a straight-through cable or a

crossed cable to a normal (non-Uplink) port on a switch or hub. This port is identical to the other 23 ports except for the ability to use a crossed or a straight-through cable.

♦ Twenty-three high-performance, NWay Ethernet ports all of which operate at 10/100 Mbps for

connections to end stations, servers and hubs. All ports can auto-negotiate between 10Mbps or 100Mbps, full or half duplex, and flow control.

Rear Panel

The rear panel of the switch consists of a slot for the optional DPS-1000 (Redundant Power Supply) and an AC power connector.

Figure 3-2. Rear panel view of the Switch

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

♦ The AC power connector is a standard three-pronged connector that supports the power cord.

Plug-in the female connector of the provided power cord into this socket, and the male side of the cord into a power outlet. Supported input voltages range from 100 ~ 240 VAC at 50 ~ 60 Hz.

Side Panels

The right side panel of the Switch contains two system fans (see the top part of the diagram below). The left side panel contains heat vents.

Figure 3-4. Side panel views of the Switch

♦ The system fans are used to dissipate heat. The sides of the system also provide heat vents to

serve the same purpose. Do not block these openings, and leave at least 6 inches of space at the rear and sides of the switch for proper ventilation. Be reminded that without proper heat dissipation and air circulation, system components might overheat, which could lead to system failure.

Optional Plug-in Modules

The DES 3326 24-port Fast Ethernet Layer 3 Switch is able to accommodate a range of optional plug-in modules in order to increase functionality and performance. These modules must be purchased separately.

1000BASE-T Module

Figure 3-5. 1000BASE-TX two-port module

♦ Front-panel module. ♦ Connects to 1000BASE-T devices. ♦ Supports Category 5e UTP or STP cable connections of up to 100 meters.

1000BASE-SX Fiber Module

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 3-6. 1000BASE-SX two-port module

♦ Front-panel module.

♦ Connects to 1000BASE-SX devices at full duplex.

♦ Allows connections using multi-mode fiber optic cable in the following configurations:

Modal bandwidth

(min. overfilled launch)

Unit: MHz*km

Operating distance

Unit: meters

Channel insertion loss

Unit: dB

62.5µm 62.5µm 50µm 50µm

160 200 400 500

220 275 500 550

2.33 2.53 3.25 3.43

1000BASE-LX Fiber Module

Figure 3-7. 1000BASE-LX two-port module

♦ Front-panel module.

♦ Connects to 1000BASE-LX devices at full duplex.

♦ Supports multi-mode fiber-optic cable connections of up to 550 meters or 5 km single-mode fiber-

optic cable connections.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

GBIC Two-Port Module

Figure 3-8. GBIC two-port module

♦ Front-panel module.

♦ Connects to GBIC devices at full duplex only.

♦ Allows multi-mode fiber optic connections of up to 550 m (SX and LX) and single-mode fiber optic

connections of up to 5 km (LX only). GBIC modules are available in –SX and –LX fiber optic media.

LED Indicators

The LED indicators of the Switch include Power, Console, and Link/Act. The following shows the LED indicators for the Switch along with an explanation of each indicator.

Figure 3-9. The LED indicators

♦ Power This indicator on the front panel should be lit during the Power-On Self Test (POST). It will

light green approximately 2 seconds after the switch is powered on to indicate the ready state of the device.

♦ Console This indicator is lit green when the switch is being managed via out-of-band/local

console management through the RS-232 console port using a straight-through serial cable.

♦ Link/Act These indicators are located to the left and right of each port. They are lit when there is

a secure connection (or link) to a device at any of the ports. The LEDs blink whenever there is reception or transmission (i.e. Activity--Act) of data occurring at a port.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

CONNECTING THE SWITCH

This chapter describes how to connect the DES 3326 to your Fast Ethernet network.

Switch to End Node

End nodes include PCs outfitted with a 10, 100 or 10/100 Mbps RJ-45 Ethernet/Fast Ethernet Network Interface Card (NIC) and most routers. The RJ-45 UTP ports on NICs and most routers are MDI-II. When using a normal straight-through cable, an MDI-II port must connect to an MDI-X port.

An end node can be connected to the Switch via a two-pair Category 3, 4, 5 UTP/STP straight cable (be sure to use Category 5e UTP or STP cabling for 100 Mbps Fast Ethernet connections). The end node should be connected to any of the twenty-three ports (2x - 24x) of the DES-3326 or to either of the two 100BASE-TX ports on the front-panel module that came preinstalled on the switch. Port 1x can be used as an uplink port to connect to another switch using either a crossed or a straight-through cable. This port is switched between MDI-X and MDI-II to accommodate either type of cable.

Figure 4-1. Switch connected to an End Node

The LED indicators for the port the end node is connected to are lit according to the capabilities of the NIC. If LED indicators are not illuminated after making a proper connection, check the PC’s LAN card, the cable, switch conditions, and connections.

The following LED indicator states are possible for an end node to switch connection:

1. The 100 LED indicator comes ON for a 100 Mbps and stays OFF for 10 Mbps.

2. The Link/Act LED indicator lights up upon hooking up a PC that is powered on.

Switch to Hub or Switch

These connections can be accomplished in a number of ways. The most important consideration is that when using a normal, straight-through cable, the connection should be made between a normal crossed port (Port 2x, 3x, etc.) and an Uplink (MDI-II) port. If you are using a crossover cable, the connection must be made from Uplink to Uplink (port 1x on the DES-3326), or from a crossed port to another crossed port.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

♦ A 10BASE-T hub or switch can be connected to the Switch via a two-pair Category 3, 4 or 5

UTP/STP straight cable.

♦ A 100BASE-TX hub or switch can be connected to the Switch via a two-pair Category 5e UTP/STP

straight cable.

If the other switch or hub contains an unused Uplink port, we suggest connecting the other device’s Uplink (MDI-II) port to any of the switch’s (MDI-X) ports (1x - 22x, or one of the optional Gigabit module ports) using a normal straight-through cable, as shown below.

If the other device does not have an unused Uplink port, make the connection with a normal straightthrough cable from the Uplink port on the switch to any normal crossed port on the hub. Alternatively, if you have a crossover cable you can save the Uplink ports for other connections and make this one from a crossed port to another crossed port.

Figure 4-2. Switch connected to a normal (non-Uplink) port on a hub or switch using a straight or crossover

cable

10BASE-T Device

For a 10BASE-T device, the Switch’s LED indicators should display the following:

♦ 100 LED speed indicator is OFF.

♦ Link/Act indicator is ON.

100BASE-TX Device

For a 100BASE-TX device, the Switch’s LED indicators should display the following:

♦ 100 LED speed indicator is ON.

♦ Link/Act is ON.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

SWITCH MANAGEMENT AND OPERATING

CONCEPTS

This chapter discusses many of the concepts and features used to manage the switch, as well as the concepts necessary for the user to understand the functioning of the switch. Further, this chapter explains many important points regarding these features.

Configuring the switch to implement these concepts and make use of its many features is discussed in detail in the next chapters.

Local Console Management

A local console is a terminal or a workstation running a terminal emulation program that is connected directly to the switch via the RS-232 console port on the front of the switch. A console connection is referred to as an ‘Out-of-Band’ connection, meaning that console is connected to the switch using a different circuit than that used for normal network communications. So, the console can be used to set up and manage the switch even if the network is down.

Local console management uses the terminal connection to operate the console program built-in to the switch (see Chapter 6, “Using the Console Interface”). A network administrator can manage, control and monitor the switch from the console program.

The DES-3326 contains a CPU, memory for data storage, flash memory for configuration data, operational programs, and SNMP agent firmware. These components allow the switch to be actively managed and monitored from either the console port or the network itself (out-of-band, or in-band).

Diagnostic (console) port (RS-232 DCE)

Out-of-band management requires connecting a terminal, such as a VT-100 or a PC running a terminal emulation program (such as HyperTerminal, which is automatically installed with Microsoft Windows) a to the RS-232 DCE console port of the Switch. Switch management using the RS-232 DCE console port is called Local Console Management to differentiate it from management performed via management platforms, such as D-View, HP OpenView, etc. Web-based Management describes management of the switch performed over the network (in-band) using the switch’s built-in Web-based management program (see Chapter 7, “Web-based Network Management”). The operations to be performed and the facilities provided by these two built-in programs are identical.

The console port is set at the factory for the following configuration:

• Baud rate: 9,600

• Data width: 8 bits

• Parity: none

• Stop bits: 1

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Flow Control None

Make sure the terminal or PC you are using to make this connection is configured to match these settings.

If you are having problems making this connection on a PC, make sure the emulation is set to VT-

100. If you still don’t see anything, try hitting <Ctrl> + r to refresh the screen.

IP Addresses and SNMP Community Names

Each Switch must be assigned its own IP Address, which is used for communication with an SNMP network manager or other TCP/IP application (for example BOOTP, TFTP). The switch’s default IP address is 10.90.90.90. You can change the default Switch IP Address to meet the specification of your networking address scheme.

The switch is also assigned a unique MAC address by the factory. This MAC address cannot be changed, and can be found from the initial boot console screen – shown below.

Figure 5-1. Boot screen

The switch’s MAC address can also be found from the console program under the Switch Information menu item, as shown below.

Figure 5-2. Switch Information screen

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

In addition, you can also set an IP Address for a gateway router. This becomes necessary when the network management station is located on a different IP network from the Switch, making it necessary for management packets to go through a router to reach the network manager, and vice-versa.

For security, you can set in the Switch a list of IP Addresses of the network managers that you allow to manage the Switch. You can also change the default SNMP Community Strings in the Switch and set the access rights of these Community Strings. In addition, a VLAN may be designated as a Management VLAN.

Traps

Traps are messages that alert you of events that occur on the Switch. The events can be as serious as a reboot (someone accidentally turned OFF the Switch), or less serious like a port status change. The Switch generates traps and sends them to the network manager (trap recipient).

Trap recipients are special users of the network who are given certain rights and access in overseeing the maintenance of the network. Trap recipients will receive traps sent from the Switch; they must immediately take certain actions to avoid future failure or breakdown of the network.

You can also specify which network managers may receive traps from the Switch by entering a list of the IP addresses of authorized network managers. Up to four trap recipient IP addresses, and four corresponding SNMP community strings can be entered.

SNMP community strings function like passwords in that the community string entered for a given IP address must be used in the management station software, or a trap will be sent.

The following are trap types the switch can send to a trap recipient:

• Cold Start This trap signifies that the Switch has been powered up and initialized such that software settings are reconfigured and hardware systems are rebooted. A cold start is different from a factory reset in that configuration settings saved to non-volatile RAM used to reconfigure the switch.

• Warm Start This trap signifies that the Switch has been rebooted, however the POST (Power On Self-Test) is skipped.

• Authentication Failure This trap signifies that someone has tried to logon to the switch using an invalid SNMP community string. The switch automatically stores the source IP address of the unauthorized user.

• New Root This trap indicates that the Switch has become the new root of the Spanning Tree, the trap is sent by the switch soon after its election as the new root. This implies that upon expiration of the Topology Change Timer the new root trap is sent out immediately after the Switch’s election as the new root.

• Topology Change (STP) A Topology Change trap is sent by the Switch when any of its configured ports transitions from the Learning state to the Forwarding state, or from the Forwarding state to the Blocking state. The trap is not sent if a new root trap is sent for the same transition.

• Link Up This trap is sent whenever the link of a port changes from link down to link up.

• Link Down This trap is sent whenever the link of a port changes from link up to link down.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

SNMP

The Simple Network Management Protocol (SNMP) is an OSI layer 7 (the application layer) protocol for remotely monitoring and configuring network devices. SNMP enables network management stations to read and modify the settings of gateways, routers, switches, and other network devices. SNMP can be used to perform many of the same functions as a directly connected console, or can be used within an integrated network management software package such as DView or NetView.

SNMP performs the following functions:

• Sending and receiving SNMP packets through the IP protocol.

• Collecting information about the status and current configuration of network devices.

• Modifying the configuration of network devices.

The DES-3326 has a software program called an ‘agent’ that processes SNMP requests, but the user program that makes the requests and collects the responses runs on a management station (a designated computer on the network). The SNMP agent and the user program both use the UDP/IP protocol to exchange packets.

Authentication

The authentication protocol ensures that both the router SNMP agent and the remote user SNMP application program discard packets from unauthorized users. Authentication is accomplished using ‘community strings’, which function like passwords. The remote user SNMP application and the router SNMP must use the same community string. SNMP community strings of up to 20 characters may be entered under the Remote Management Setup menu of the console program.

Traps

Traps are messages that alert network personnel of events that occur on the Switch. The events can be as serious as a reboot (someone accidentally turned OFF the Switch), or less serious like a port status change. The Switch generates traps and sends them to the trap recipient (or network manager).

SNMP community strings function like passwords in that the community string entered for a given IP address must be used in the management station software, or a trap will be sent.

The following are trap types the switch can send to a trap recipient:

• Warm Start This trap signifies that the Switch has been rebooted, however the POST (Power On Self-Test) is skipped.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Topology Change A Topology Change trap is sent by the Switch when any of its configured ports transitions from the Learning state to the Forwarding state, or from the Forwarding state to the Blocking state. The trap is not sent if a new root trap is sent for the same transition.

• Link Change Event This trap is sent whenever the link of a port changes from link up to link down or from link down to link up.

• Port Partition This trap is sent whenever the port state enters the partition mode (or automatic partitioning, port disable) when more than thirty-two collisions occur while transmitting at 10Mbps or more than sixty-four collisions occur while transmitting at 100Mbps.

• Broadcast\Multicast Storm This trap is sent whenever the port reaches the threshold (in packets per second) set globally for the switch. Counters are maintained for each port, and separate counters are maintained for broadcast and multicast packets. The switch’s default setting is 128 kpps for both broadcast and multicast packets.

MIBs

Management and counter information are stored in the Switch in the Management Information Base (MIB). The Switch uses the standard MIB-II Management Information Base module. Consequently, values for MIB objects can be retrieved from any SNMP-based network management software. In addition to the standard MIB-II, the Switch also supports its own proprietary enterprise MIB as an extended Management Information Base. These MIBs may also be retrieved by specifying the MIB’s Object-Identity (OID) at the network manager. MIB values can be either read-only or read-write.

Read-only MIBs variables can be either constants that are programmed into the Switch, or variables that change while the Switch is in operation. Examples of read-only constants are the number of port and type of ports. Examples of read-only variables are the statistics counters such as the number of errors that have occurred, or how many kilobytes of data have been received and forwarded through a port.

Read-write MIBs are variables usually related to user-customized configurations. Examples of these are the Switch’s IP Address, Spanning Tree Algorithm parameters, and port status.

If you use a third-party vendors’ SNMP software to manage the Switch, a diskette listing the Switch’s propriety enterprise MIBs can be obtained by request. If your software provides functions to browse or modify MIBs, you can also get the MIB values and change them (if the MIBs’ attributes permit the write operation). This process however can be quite involved, since you must know the MIB OIDs and retrieve them one by one.

Packet Forwarding

The Switch enters the relationship between destination MAC or IP addresses and the Ethernet port or gateway router the destination resides on into its forwarding table. This information is then used to forward packets. This reduces the traffic congestion on the network, because packets, instead of being

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

transmitted to all ports, are transmitted to the destination port only. Example: if Port 1 receives a packet destined for a station on Port 2, the Switch transmits that packet through Port 2 only, and transmits nothing through the other ports. This process is referred to as ‘learning’ the network topology.

MAC Address Aging Time

The Aging Time affects the learning process of the Switch. Dynamic forwarding table entries, which are made up of the source MAC addresses and their associated port numbers, are deleted from the table if they are not accessed within the aging time.

The aging time can be from 10 to 1,000,000 seconds with a default value of 300 seconds. A very long aging time can result in dynamic forwarding table entries that are out-of-date or no longer exist. This may cause incorrect packet forwarding decisions by the switch.

If the Aging Time is too short however, many entries may be aged out too soon. This will result in a high percentage of received packets whose source addresses cannot be found in the forwarding table, in which case the switch will broadcast the packet to all ports, negating many of the benefits of having a switch.

Static forwarding entries are not affected by the aging time.

Filtering

The switch uses a filtering database to segment the network and control communication between segments. It can also filter packets off the network for intrusion control. Static filtering entries can be made by either MAC address or IP address filtering.

Each port on the switch is a unique collision domain and the switch filters (discards) packets whose destination lies on the same port as where it originated. This keeps local packets from disrupting communications on other parts of the network.

For intrusion control, whenever a switch encounters a packet originating from or destined to a MAC address or an IP Address entered into the filter table, the switch will discard the packet.

Some filtering is done automatically by the switch:

• Dynamic filtering – automatic learning and aging of MAC addresses and their location on the network. Filtering occurs to keep local traffic confined to its segment.

• Filtering done by the Spanning Tree Protocol, which can filter packets based on topology, making sure that signal loops don’t occur.

• Filtering done for VLAN integrity. Packets from a member of a VLAN (VLAN 2, for example) destined for a device on another VLAN (VLAN 3) will be filtered.

Some filtering requires the manual entry of information into a filtering table:

• MAC address filtering – the manual entry of specific MAC addresses to be filtered from the network. Packets sent from one manually entered MAC address can be filtered from the network. The entry may be specified as a source, a destination, or both.

• IP address filtering – the manual entry of specific IP addresses to be filtered from the network (switch must be in IP Routing mode). Packets sent from one manually entered IP address to

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

another can be filtered from the network. The entry may specified as a source, a destination, or both (switch must be in IP Routing mode).

Spanning Tree

The IEEE 802.1D Spanning Tree Protocol allows for the blocking of links between switches that form loops within the network. When multiple links between switches are detected, a primary link is established. Duplicated links are blocked from use and become standby links. The protocol allows for the duplicate links to be used in the event of a failure of the primary link. Once the Spanning Tree Protocol is configured and enabled, primary links are established and duplicated links are blocked automatically. The reactivation of the blocked links (at the time of a primary link failure) is also accomplished automatically – without operator intervention.

The DES-3326 STP allows two levels of spanning trees to be configured. The first level constructs a spanning tree on the links between switches. This is referred to as the Switch or Global level. The second level is on a port group basis. Groups of ports are configured as being members of a spanning tree and the algorithm and protocol are applied to the group of ports. This is referred to as the Port or VLAN level.

On the switch level, STP calculates the Bridge Identifier for each switch and then sets the Root Bridge and the Designated Bridges.

On the port level, STP sets the Root Port and the Designated Ports.

The following are the user-configurable STP parameters for the switch level:

meter Description Default

Value

Bridge Identifier

(Not userconfigurable except by setting priority below)

Priority A relative priority for each

Hello Time The length of time between

A combination of the Userset priority and the switch’s MAC address. The Bridge Identifier consists of two parts: a 16-bit priority and a 48-bit Ethernet MAC address

switch – lower numbers give a higher priority and a greater chance of a given switch being elected as the root bridge

broadcasts of the hello message by the switch

32768 + MAC

32768

2 seconds

Maximum Age Timer

Forward Delay Timer

Measures the age of a received BPDU for a port and ensures that the BPDU is discarded when its age exceeds the value of the maximum age timer.

The amount time spent by a port in the learning and listenin

states waiting for a

20 seconds

15 seconds

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

BPDU that may return the port to the blocking state.

Table 5-1. STP Parameters – Switch Level

The following are the user-configurable STP parameters for the port or port group level:

Variable Description Default

Value

Port Priority A relative priority for each

port – lower numbers give a higher priority and a greater chance of a given port being elected as the root port

Port Cost A value used by STP to

evaluate paths – STP calculates path costs and selects the path with the minimum cost as the active path.

128

19 – 100Mbps Fast Ethernet ports

10 – 1000Mbps Gigabit Ethernet ports

Table 5-2. STP Parameters – Port Group Level

Bridge Protocol Data Units

For STP to arrive at a stable network topology, the following information is used:

• The unique switch identifier

• The path cost to the root associated with each switch port

• The port identifier

STP communicates between switches on the network using Bridge Protocol Data Units (BPDUs). Each BPDU contains the following information:

• The unique identifier of the switch that the transmitting switch currently believes is the root switch

• The path cost to the root from the transmitting port

• The port identifier of the transmitting port

The switch sends BPDUs to communicate and construct the spanning-tree topology. All switches connected to the LAN on which the packet is transmitted will receive the BPDU. BPDUs are not directly forwarded by the switch, rather the receiving switch uses the information in the frame to calculate a BPDU, and, if the topology changes, initiates a BPDU transmission.

The communication between switches via BPDUs results in the following:

• One switch is elected as the root switch

• The shortest distance to the root switch is calculated for each switch

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• A designated switch is selected. This is the switch closest to the root switch through which packets will be forwarded to the root.

• A port for each switch is selected. This is the port providing the best path from the switch to the root switch.

• Ports included in the STP are selected.

Creating a Stable STP Topology

If all switches have STP enabled with default settings, the switch with the lowest MAC address in the network will become the root switch. By increasing the priority (lowering the priority number) of the best switch, STP can be forced to select the best switch as the root switch.

When STP is enabled using the default parameters, the path between source and destination stations in a switched network might not be ideal. For instance, connecting higher-speed links to a port that has a higher number than the current root port can cause a root-port change. The goal is to make the fastest link the root port.

STP Port States

The BPDUs take some time to pass through a network. This propagation delay can result in topology changes where a port that transitioned directly from a Blocking state to a Forwarding state could create temporary data loops. Ports must wait for new network topology information to propagate throughout the network before starting to forward packets. They must also wait for the packet lifetime to expire for BPDU packets that were forwarded based on the old topology. The forward delay timer is used to allow the network topology to stabilize after a topology change.

In addition, STP specifies a series of states a port must transition through to further ensure that a stable network topology is created after a topology change.

Each port on a switch using STP exists is in one of the following five states:

• Blocking – the port is blocked from forwarding or receiving packets

• Listening – the port is waiting to receive BPDU packets that may tell the port to go back to the

blocking state

• Learning – the port is adding addresses to its forwarding database, but not yet forwarding packets

• Forwarding – the port is forwarding packets

• Disabled – the port only responds to network management messages and must return to the

blocking state first

A port transitions from one state to another as follows:

• From initialization (switch boot) to blocking

• From blocking to listening or to disabled

• From listening to learning or to disabled

• From learning to forwarding or to disabled

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• From forwarding to disabled

• From disabled to blocking

Figure 5-3. STP Port State Transitions

When STP is enabled, every port on every switch in the network goes through the blocking state and then transitions through the states of listening and learning at power up. If properly configured, each port stabilizes to the forwarding or blocking state.

No packets (except BPDUs) are forwarded from, or received by, STP enabled ports until the forwarding state is enabled for that port.

Default Spanning-Tree Configuration

Feature Default Value

Enable state STP enabled for all ports

Port priority 128

Port cost 19

Bridge Priority 32,768

Table 5-3. Default STP Parameters

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

User-Changeable STA Parameters

The factory default setting should cover the majority of installations. However, it is advisable to keep the default settings as set at the factory; unless, it is absolutely necessary. The user changeable parameters in the Switch are as follows:

• Priority A Priority for the switch can be set from 0 to 65535. 0 is equal to the highest Priority.

• Hello Time The Hello Time can be from 1 to 10 seconds. This is the interval between two transmissions of BPDU packets sent by the Root Bridge to tell all other Switches that it is indeed the Root Bridge. If you set a Hello Time for your Switch, and it is not the Root Bridge, the set Hello Time will be used if and when your Switch becomes the Root Bridge.

Note: The Hello Time cannot be longer than the Max. Age. Otherwise, a configuration error will occur.

• Max. Age The Max. Age can be from 6 to 40 seconds. At the end of the Max. Age, if a BPDU has still not been received from the Root Bridge, your Switch will start sending its own BPDU to all other Switches for permission to become the Root Bridge. If it turns out that your Switch has the lowest Bridge Identifier, it will become the Root Bridge.

• Forward Delay Timer The Forward Delay can be from 4 to 30 seconds. This is the time any port on the Switch spends in the listening state while moving from the blocking state to the forwarding state.

Note: Observe the following formulas when setting the above parameters:

Max. Age ≤ 2 x (Forward Delay - 1 second)

Max. Age ≥ 2 x (Hello Time + 1 second)

• Port Priority A Port Priority can be from 0 to 255. The lower the number, the greater the probability the port will be chosen as the Root Port.

• Port Cost A Port Cost can be set from 1 to 65535. The lower the number, the greater the probability the port will be chosen to forward packets.

Illustration of STP

A simple illustration of three Bridges (or three switches) connected in a loop is depicted below. In this example, you can anticipate some major network problems if the STP assistance is not applied. If Bridge A broadcasts a packet to Bridge B, Bridge B will broadcast it to Bridge C, and Bridge C will broadcast it to back to Bridge A ... and so on. The broadcast packet will be passed indefinitely in a loop, potentially causing a network failure.

STP can be applied as shown in Figure 2-4. In this example, STP breaks the loop by blocking the connection between Bridge B and C. The decision to block a particular connection is based on the STP calculation of the most current Bridge and Port settings. Now, if Bridge A broadcasts a packet to Bridge C, then Bridge C will drop the packet at port 2 and the broadcast will end there.

Setting-up STP using values other than the defaults, can be complex. Therefore, you are advised to keep the default factory settings and STP will automatically assign root bridges/ports and block loop connections. Influencing STP to choose a particular switch as the root bridge using the Priority setting, or influencing STP to choose a particular port to block using the Port Priority and Port Cost settings is, however, relatively straight forward.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 5-4. Before Applying the STA Rules

In this example, only the default STP values are used.

Figure 5-6. After Applying the STA Rules

The switch with the lowest Bridge ID (switch C) was elected the root bridge, and the ports were selected to give a high port cost between switches B and C. The two (optional) Gigabit ports (default port cost =

10) on switch A are connected to one (optional) Gigabit port on both switch B and C. The redundant link between switch B and C is deliberately chosen as a 100 Mbps Fast Ethernet link (default port cost = 19). Gigabit ports could be used, but the port cost should be increased from the default to ensure that the link between switch B and switch C is the blocked link.

Link Aggregation

Link aggregation is used to combine a number of ports together to make a single high-bandwidth data pipeline. The participating parts are called members of a link aggregation group, with one port

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

designated as the master port of the group. Since all members of the link aggregation group must be configured to operate in the same manner, the configuration of the master port is applied to all members of the link aggregation group. Thus, when configuring the ports in a link aggregation group, you only need to configure the master port.

The DES-3326 supports link aggregation groups, which may include from 2 to 8 switch ports each, except for a Gigabit link aggregation group which consists of the 2 (optional) Gigabit Ethernet ports of the front panel. These ports are the two 1000BASE-SX, -LX –TX or GBIC ports contained in a frontpanel mounted module.

Figure 5-7. Link Aggregation Group

Data transmitted to a specific host (destination address) will always be transmitted over the same port in a link aggregation group. This allows packets in a data stream to arrive in the same order they were sent. A aggregated link connection can be made with any other switch that maintains host-to-host data streams over a single link aggregate port. Switches that use a load-balancing scheme that sends the packets of a host-to-host data stream over multiple link aggregation ports cannot have a aggregated connection with the DES-3326 switch.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

VLANs

A VLAN is a collection of end nodes grouped by logic rather than physical location. End nodes that frequently communicate with each other are assigned to the same VLAN, regardless of where they are located physically on the network. Logically, a VLAN can be equated to a broadcast domain, because broadcast packets are forwarded only to members of the VLAN on which the broadcast was initiated.

Notes About VLANs on the DES-3326

1. The DES-3326 supports IEEE 802.1Q VLANs. The port untagging function can be used to remove the 802.1Q tag from packet headers to maintain compatibility with devices that are tag-unaware (that is, network devices that do not support IEEE 802.1Q VLANs or tagging).

2. The switch’s default - in both Layer 2 Only mode and IP Routing mode - is to assign all ports to a single 802.1Q VLAN named DEFAULT_VLAN.

3. The switch allows the assignment of an IP interface to each VLAN, in IP Routing mode. The VLANs must be configured before setting up the IP interfaces

4. A VLAN that is not assigned an IP interface will behave as a layer 2 VLAN – and IP routing, by the switch, will not be possible to this VLAN regardless of the switch’s operating mode.

IEEE 802.1Q VLANs

Some relevant terms:

Tagging - The act of putting 802.1Q VLAN information into the header of a packet.

Untagging - The act of stripping 802.1Q VLAN information out of the packet header.

Ingress port - A port on a switch where packets are flowing into the switch and VLAN decisions must

be made.

Egress port - A port on a switch where packets are flowing out of the switch, either to another switch or to an end station, and tagging decisions must be made.

IEEE 802.1Q (tagged) VLANs are implemented on the DES-3326 Layer 3 switch. 802.1Q VLANs require tagging, which enables the VLANs to span an entire network (assuming all switches on the network are IEEE 802.1Q-compliant).

Any port can be configured as either tagging or untagging. The untagging feature of IEEE 802.1Q VLANs allow VLANs to work with legacy switches that don’t recognize VLAN tags in packet headers. The tagging feature allows VLANs to span multiple 802.1Q-compliant switches through a single physical connection and allows Spanning Tree to be enabled on all ports and work normally.

802.1Q VLAN Packet Forwarding

Packet forwarding decisions are made based upon the following three types of rules:

• Ingress rules – rules relevant to the classification of received frames belonging to a VLAN.

• Forwarding rules between ports – decides filter or forward the packet

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Egress rules – determines if the packet must be sent tagged or untagged.

Figure 5-8. IEEE 802.1Q Packet Forwarding

802.1Q VLAN Tags

The figure below shows the 802.1Q VLAN tag. There are four additional octets inserted after the source MAC address. Their presence is indicated by a value of 0x8100 in the EtherType field. When a packet’s EtherType field is equal to 0x8100, the packet carries the IEEE 802.1Q/802.1p tag. The tag is contained in the following two octets and consists of 3 bits or user priority, 1 bit of Canonical Format Identifier (CFI – used for encapsulating Token Ring packets so they can be carried across Ethernet backbones) and 12 bits of VLAN ID (VID). The 3 bits of user priority are used by 802.1p. The VID is the VLAN identifier and is used by the 802.1Q standard. Because the VID is 12 bits long, 4094 unique VLANs can be identified.

The tag is inserted into the packet header making the entire packet longer by 4 octets. All of the information contained in the packet originally is retained.

Figure 5-9. IEEE 802.1Q Tag

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The EtherType and VLAN ID are inserted after the MAC source address, but before the original EtherType/Length or Logical Link Control. Because the packet is now a bit longer than it was originally, the Cyclic Redundancy Check (CRC) must be recalculated.

Figure 5-10. Adding an IEEE 802.1Q Tag

Port VLAN ID

Packets that are tagged (are carrying the 802.1Q VID information) can be transmitted from one 802.1Q compliant network device to another with the VLAN information intact. This allows 802.1Q VLANs to span network devices (and indeed, the entire network – if all network devices are 802.1Q compliant).

Unfortunately, not all network devices are 802.1Q compliant. These devices are referred to as tag- unaware. 802.1Q devices are referred to as tag-aware.

Prior to the adoption 802.1Q VLANs, port-based and MAC-based VLANs were in common use. These VLANs relied upon a Port VLAN ID (PVID) to forward packets. A packet received on a given port would be assigned that port’s PVID and then be forwarded to the port that corresponded to the packet’s destination address (found in the switch’s forwarding table). If the PVID of the port that received the packet is different from the PVID of the port that is to transmit the packet, the switch will drop the packet.

Within the switch, different PVIDs mean different VLANs (remember that two VLANs cannot communicate without an external router). So, VLAN identification based upon the PVIDs cannot create VLANs that extend outside a given switch (or switch stack).

Every physical port on a switch has a PVID. 802.1Q ports are also assigned a PVID, for use within the switch. If no VLANs are defined on the switch, all ports are then assigned to a default VLAN with a PVID equal to 1. Untagged packets are assigned the PVID of the port on which they were received. Forwarding decisions are based upon this PVID, in so far as VLANs are concerned. Tagged packets are forwarded according to the VID contained within the tag. Tagged packets are also assigned a PVID, but the PVID is not used to make packet forwarding decisions, the VID is.

Tag-aware switches must keep a table to relate PVIDs within the switch to VIDs on the network. The switch will compare the VID of a packet to be transmitted to the VID of the port that is to transmit the packet. If the two VIDs are different, the switch will drop the packet. Because of the existence of the PVID for untagged packets and the VID for tagged packets, tag-aware and tag-unaware network devices can coexist on the same network.

A switch port can have only one PVID, but can have as many VIDs as the switch has memory in its VLAN table to store them.

Because some devices on a network may be tag-unaware, a decision must be made at each port on a tag-aware device before packets are transmitted – should the packet to be transmitted have a tag or

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

not? If the transmitting port is connected to a tag-unaware device, the packet should be untagged. If the transmitting port is connected to a tag-aware device, the packet should be tagged.

Tagging and Untagging

Every port on an 802.1Q compliant switch can be configured as tagging or untagging.

Ports with tagging enabled will put the VID number, priority and other VLAN information into the header of all packets that flow into and out of it. If a packet has previously been tagged, the port will not alter the packet, thus keeping the VLAN information intact. The VLAN information in the tag can then be used by other 802.1Q compliant devices on the network to make packet forwarding decisions.

Ports with untagging enabled will strip the 802.1Q tag from all packets that flow into and out of those ports. If the packet doesn’t have an 802.1Q VLAN tag, the port will not alter the packet. Thus, all packets received by and forwarded by an untagging port will have no 802.1Q VLAN information. (Remember that the PVID is only used internally within the switch). Untagging is used to send packets from an 802.1Q-compliant network device to a non-compliant network device.

Ingress Filtering

A port on a switch where packets are flowing into the switch and VLAN decisions must be made is referred to as an ingress port. If ingress filtering is enabled for a port, the switch will examine the VLAN information in the packet header (if present) and decide whether or not to forward the packet.

If the packet is tagged with VLAN information, the ingress port will first determine if the ingress port itself is a member of the tagged VLAN. If it is not, the packet will be dropped. If the ingress port is a member of the 802.1Q VLAN, the switch then determines if the destination port is a member of the

802.1Q VLAN. If it is not, the packet is dropped. If the destination port is a member of the 802.1Q VLAN, the packet is forwarded and the destination port transmits it to its attached network segment.

If the packet is not tagged with VLAN information, the ingress port will tag the packet with its own PVID as a VID (if the port is a tagging port). The switch then determines if the destination port is a member of the same VLAN (has the same VID) as the ingress port. If it does not, the packet is dropped. If it has the same VID, the packet is forwarded and the destination port transmits it on its attached network segment.

This process is referred to as ingress filtering and is used to conserve bandwidth within the switch by dropping packets that are not on the same VLAN as the ingress port at the point of reception. This eliminates the subsequent processing of packets that will just be dropped by the destination port.

VLANs in Layer 2 Only Mode

The switch initially configures one VLAN, VID = 1, called the DEFAULT_VLAN. The factory default setting assigns all ports on the switch to the DEFAULT_VLAN.

Packets cannot cross VLANs if the switch is in Layer 2 Only mode. If a member of one VLAN wants to connect to another VLAN, the link must be through an external router.

When the switch is in Layer 2 Only mode, 802.1Q VLANs are supported.

If no VLANs are configured on the switch and the switch is in Layer 2 Only mode, then all packets will be forwarded to any destination port. Packets with unknown source addresses will be flooded to all ports. Broadcast and multicast packets will also be flooded to all ports.

A VLAN that does not have a corresponding IP interface defined for it, will function as a Layer 2 Only VLAN – regardless of the Switch Operation mode.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Layer 3-Based VLANs

Layer 3-based VLANs use network-layer addresses (subnet address for TCP/IP) to determine VLAN membership. These VLANs are based on layer 3 information, but this does not constitute a ‘routing’ function.

The DES-3326 allows an IP subnet to be configured for each 802.1Q VLAN that exists on the switch.

Even though a switch inspects a packet’s IP address to determine VLAN membership, no route calculation is performed, the RIP protocol is not employed, and packets traversing the switch are bridged using the Spanning Tree algorithm.

A switch that implements layer 3 (or ‘subnet’) VLANs without performing any routing function between these VLANs is referred to as performing ‘IP Switching’.

IP Addressing and Subnetting

This section gives basic information needed to configure your Layer 3 switch for IP routing. The information includes how IP addresses are broken down and how subnetting works. You will learn how to assign each interface on the router an IP address with a unique subnet.

Definitions

• IP Address – the unique number ID assigned to each host or interface on a network. IP addresses have the form xxx.xxx.xxx.xxx.

• Subnet – a portion of a network sharing a particular network address.

• Subnet mask – a 32-bit number used to describe which portion of a Network Address refers to

the subnet and which portion refers to the host. Subnet masks have the form xxx.xxx.xxx.xxx.

• Interface – a network connection

• IP Interface – another name for subnet.

• Network Address – the resulting 32-bit number from a bitwise logical AND operation performed

between an IP address and a subnet mask.

• Subnet Address – another name for network address.

IP Addresses

The Internet Protocol (IP) was designed for routing data between network sites. Later, it was adapted for routing between networks (referred to as “subnets”) within a site. The IP defines a way of generating a unique number that can be assigned each network in the internet and each of the computers on each of those networks. This number is called the IP address.

IP addresses use a “dotted decimal” notation. Here are some examples of IP addresses written in this format:

1. 210.202.204.205

2. 189.21.241.56

3. 125.87.0.1

This allows IP address to be written in a string of 4 decimal (base 10) numbers. Computers can only understand binary (base 2) numbers, and these binary numbers are usually grouped together in bytes, or eight bits. (A bit is a binary digit – either a “1” or a “0”). The dots (periods) simply make the IP

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

address easier to read. A computer sees an IP address not as four decimal numbers, but as a long string of binary digits (32 binary digits or 32 bits, IP addresses are 32-bit addresses).

The three IP addresses in the example above, written in binary form are:

1. 11010010.11001010.11001100.11001101

2. 10111101.00010101.11110001.00111000

3. 01111101.01010111.00000000.00000001

The dots are included to make the numbers easier to read.

Eight binary bits are called a ‘byte’ or an ‘octet’. An octet can represent any decimal value between ‘0’ (00000000) and ‘255’ (11111111). IP addresses, represented in decimal form, are four numbers whose value is between ‘0’ to ‘255’. The total range of IP addresses are then:

Lowest possible IP address - 0.0.0.0 Highest possible IP address - 255.255.255.255

To convert decimal numbers to 8-bit binary numbers (and vice-versa), you can use the following chart:

Binary Octet Digit 2

26 25 24 23 22 21 2

Decimal Equivalent 128 64 32 16 8 4 2 1

Binary Number

1 1 1 1 1 1 1 1

128+64+32+16+8+4+2+1=

255

Table 5-4. Binary to Decimal Conversion

Each digit in an 8-bit binary number (an octet) represents a power of two. The left-most digit represents 2 raised to the 7

power (2x2x2x2x2x2x2=128) while the right-most digit represents 2 raised to the 0th

power (any number raised to the 0th power is equal to one, by definition).

IP addresses actually consist of two parts, one identifying the network and one identifying the destination (node) within the network.

The IP address discussed above is one part and a second number called the Subnet mask is the other part. To make this a bit more confusing, the subnet mask has the same numerical form as an IP address.

Address Classes

Address classes refer to the range of numbers in the subnet mask. Grouping the subnet masks into classes makes the task of dividing a network into subnets a bit easier.

There are 5 address classes. The first 4 bits in the IP address determine which class the IP address falls in.

• Class A addresses begin with 0xxx, or 1 to 126 decimal.

• Class B addresses begin with 10xx, or 128 to 191 decimal.

• Class C addresses begin with 110x, or 192 to 223 decimal.

• Class D addresses begin with 1110, or 224 to 239 decimal.

• Class E addresses begin with 1111, or 240 to 254 decimal.

Addresses beginning with 01111111, or 127 decimal, are reserved. They are used for internal testing on a local machine (called loopback). The address 127.0.0.1 can always be pinged from a local node because it forms a loopback and points back to the same node.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Class D addresses are reserved for multicasting.

Class E Addresses are reserved for future use. They are not used for node addresses.

The part of the IP address that belongs to the network is the part that is ‘hidden’ by the ‘1’s in the subnet mask. This can be seen below:

• Class A NETWORK.node.node.node

• Class B NETWORK.NETWORK.node.node

• Class C NETWORK.NETWORK.NETWORK.node

For example, the IP address 10.42.73.210 is a Class A address, so the Network part of the address (called the Network Address) is the first octet (10.x.x.x). The node part of the address is the last three octets (x.42.73.210).

To specify the network address for a given IP address, the node part is set to all “0”s. In our example,

10.0.0.0 specifies the network address for 10.42.73.210. When the node part is set to all “1”s, the address specifies a broadcast address. So, 10.255.255.255 is the broadcast address for the network

10.0.0.0.

Subnet Masking

A subnet mask can be applied to an IP address to identify the network and the node parts of the address. A bitwise logical AND operation between the IP address and the subnet mask results in the Network Address.

For example:

00001010.00101010.01001001.11010010 10.42.73.210 Class A IP address

11111111.00000000.00000000.00000000 255.0.0.0 Class A Subnet Mask

00001010.00000000.00000000.00000000 10.0.0.0 Network Address The Default subnet masks are:

• Class A – 11111111.00000000.00000000.00000000 255.0.0.0

• Class B – 11111111.11111111.00000000.00000000 255.255.0.0

• Class C – 1111111.11111111.11111111.00000000 255.255.255.0

Additional bits can be added to the default subnet mask for a given Class to further subnet a network. When a bitwise logical AND operation is performed between the subnet mask and the IP address, the result defines the Subnet Address.

Some restrictions apply to subnet addresses. Addresses of all “0”s and all “1”s are reserved for the local network (when a host does not know it’s network address) and for all hosts on the network (the broadcast address). This also applies to subnets. A subnet address cannot be all “0”s or all “1”s. A 1bit subnet mask is also not allowed.

Calculating the Number of Subnets and Nodes

To calculate the number of subnets and nodes, use the formula (2n – 2) where n = the number of bits in either the subnet mask or the node portion of the IP address. Multiplying the number of subnets by the number of nodes available per subnet gives the total number of nodes for the entire network.

Example

00001010.00101010.01001001.11010010 10.42.73.210 Class A IP address

11111111.11100000.00000000.00000000 255.224.0.0 Subnet Mask

00001010.00100000.00000000.00000000 10.32.0.0 Network Address

00001010.00101010.11111111.11111111 10.32.255.255 Broadcast Address

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

This example uses an 11-bit subnet mask. (There are 3 additional bits added to the default Class A subnet mask). So the number of subnets is:

– 2 = 8 – 2 = 6

Subnets of all “0”s and all “1”s are not allowed, so 2 subnets are subtracted from the total.

The number of bits used in the node part of the address is 24 – 3 = 21 bits, so the total number of nodes is:

– 2 = 2,097,152 – 2 = 2,097,150

Multiplying the number of subnets times the number of nodes gives 12,582,900 possible nodes.

Note that this is less than the 16,777,214 possible nodes that an unsubnetted class A network would have.

Subnetting reduces the number of possible nodes for a given network, but increases the segmentation of the network.

Classless InterDomain Routing – CIDR

Under CIDR, the subnet mask notation is reduced to a simplified shorthand. Instead of specifying all of the bits of the subnet mask, it is simply listed as the number of contiguous “1”s (bits) in the network portion of the address. Look at the subnet mask of the above example in binary -

11111111.11100000.00000000.00000000 – and you can see that there are 11 “1”s or 11 bits used to mask the network address from the node address. Written in CIDR notation this becomes:

10.32.0.0/11

# of

Subnet Mask CID

Bits

2 255.192.0.0 /10 2 4194302 8388604 3 255.224.0.0 /11 6 2097150 12582900 4 255.240.0.0 /12 14 1048574 14680036 5 255.248.0.0 /13 30 524286 15728580 6 255.252.0.0 /14 62 262142 16252804 7 255.254.0.0 /15 126 131070 16514820 8 255.255.0.0 /16 254 65534 16645636 9 255.255.128.0 /17 510 32766 16710660 10 255.255.192.0 /18 1022 16382 16742404 11 255.255.224.0 /19 2046 8190 16756740 12 255.255.240.0 /20 4094 4094 16760836 13 255.255.248.0 /21 8190 2046 16756740 14 255.255.252.0 /22 16382 1022 16742404 15 255.255.254.0 /23 32766 510 16710660 16 255.255.255.0 /24 65534 254 16645636 17 255.255.255.1

18 255.255.255.1

19 255.255.255.2

20 255.255.255.2

21 255.255.255.2

22 255.255.255.2

# of

Subnets Nota tion

/25 131070 126 16514820

/26 262142 62 16252804

/27 525286 30 15728580

/28 1048574 14 14680036

/29 2097150 6 12582900

/30 4194302 2 8388604

# of Hosts Total Hosts

Table 5-5. Class A Subnet Masks

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

# of

Subnet Mask CIDR Bits 2 255.255.192 /18 2 16382 32764 3 255.255.224.0 /19 6 8190 49140 4 255.255.240.0 /20 14 4094 57316 5 255.255.248.0 /21 30 2046 61380 6 255.255.252.0 /22 62 1022 63364 7 255.255.254.0 /23 126 510 64260 8 255.255.255.0 /24 254 254 64516 9 255.255.255.128 /25 510 126 64260 10 255.255.255.192 /26 1022 62 63364 11 255.255.255.224 /27 2046 30 61380 12 255.255.255.240 /28 4094 14 57316 13 255.255.255.248 /29 8190 6 49140 14 255.255.255.252 /30 16382 2 32764

Table 5-6. Class B Subnet Masks

# of

Subnet Mask CIDR Bits 2 255.255.255.192 /26 2 62 124 3 255.255.255.224 /27 6 30 180 4 255.255.255.240 /28 14 14 196 5 255.255.255.248 /29 30 6 180 6 255.255.255.252 /30 62 2 124

Table 5-7. Class C Subnet Masks

Notation

# of Subnets

# of Hosts

Total Hosts

Setting up IP Interfaces

The Layer 3 switch allows ranges of IP addresses (OSI layer 3) to be assigned to VLANs (OSI layer 2). Each VLAN must be configured prior to setting up the corresponding IP interface. An IP addressing scheme must then be established, and implemented when the IP interfaces are set up on the switch.

An example is presented below:

VLAN Name VID Switch Ports

System (default) 1 5, 6, 7, 8, 21, 22, 23, 24

Engineering 2 9, 10, 11, 12

Marketing 3 13, 14, 15, 16

Finance 4 17, 18, 19, 20

Sales 5 1, 2, 3, 4

Backbone 6 25, 26

Table 5-8. VLAN Example – Assigned Ports

In this case, 6 IP interfaces are required, so a CIDR notation of 10.32.0.0/11 (or a 11-bit) addressing scheme will work. This addressing scheme will give a subnet mask of

11111111.11100000.00000000.00000000 (binary) or 255.224.0.0 (decimal).

Using a 10.xxx.xxx.xxx IP address notation, the above example would give 6 network addresses and 6 subnets.

Any IP address from the allowed range of IP addresses for each subnet can be chosen as an IP address for an IP interface on the switch.

For this example, we have chosen the next IP address above the network address:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

VLAN Name VID Network Address IP Address

System (default) 1 10.32.0.0 10.32.0.1

Engineering 2 10.64.0.0 10.64.0.1

Marketing 3 10.96.0.0 10.96.0.1

Finance 4 10.128.0.0 10.128.0.1

Sales 5 10.160.0.0 10.160.0.1

Backbone 6 10.192.0.0 10.192.0.1

Table 5-9. VLAN Example – Assigned IP Addresses

The 6 IP interfaces, each with an IP address (listed in the table above), and a subnet mask of

255.224.0.0 can be entered into the Setup IP Interface menu.

Layer 3-Based VLANs

The DES-3326 allows an IP subnet to be configured for each 802.1Q VLAN that exists on the switch.

A switch that implements layer 3 (or ‘subnet’) VLANs without performing any routing function between these VLANs is referred to as performing ‘IP Switching’.

Internet Protocols

This is a brief introduction to the suite of Internet Protocols frequently referred to as TCP/IP. It is intended to give the reader a reasonable understanding of the available facilities and some familiarity with terminology. It is not intended to be a complete description.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Protocol Layering

The Internet Protocol (IP) divides the tasks necessary to route and forward packets across networks by using a layered approach. Each layer has clearly defined tasks, protocol, and interfaces for communicating with adjacent layers, but the exact way these tasks are accomplished is left to individual software designers. The Open Systems Interconnect (OSI) seven-layer model has been adopted as the reference for the description of modern networking, including the Internet.

A diagram of the OSI model is shown below (note that this is not a complete listing of the protocols contained within each layer of the model):

Figure 5-11. OSI Seven Layer Network Model

Each layer is a distinct set of programs executing a distinct set of protocols designed to accomplish some necessary tasks. They are separated from the other layers within the same system or network, but must communicate and interoperate. This requires very well-defined and well-known methods for transferring messages and data. This is accomplished through the protocol stack.

Protocol layering as simply a tool for visualizing the organization of the necessary software and hardware in a network. In this view, Layer 2 represents switching and Layer 3 represents routing. Protocol layering is actually a set of guidelines used in writing programs and designing hardware that delegate network functions and allow the layers to communicate. How these layers communicate within a stack (for example, within a given computer) is left to the operating system programmers.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 5-12. The Protocol Stack

Between two protocol stacks, members of the same layer are known as peers and communicate by wellknown (open and published) protocols. Within a protocol stack, adjacent layers communicate by an internal interface. This interface is usually not publicly documented and is frequently proprietary. It has some of the same characteristics of a protocol and two stacks from the same software vendor may communicate in the same way. Two stacks from different software vendors (or different products from the same vendor) may communicate in completely different ways. As long as peers can communicate and interoperate, this has no impact on the functioning of the network.

The communication between layers within a given protocol stack can be both different from a second stack and proprietary, but communication between peers on the same OSI layer is open and consistent.

A brief description of the most commonly used functional layers is helpful to understand the scope of how protocol layering works.

Layer 1

This is referred to as the physical layer. It handles the electrical connections and signaling required to make a physical link from one point in the network to another. It is on this layer that the unique Media Access Control (MAC) address is defined.

Layer 2

This layer, commonly called the switching layer, allows end station addressing and the establishment of connections between them.

Layer 2 switching forwards packets based on the unique MAC address of each end station and offers high-performance, dedicated-bandwidth of Fast or Gigibit Ethernet within the network.

Layer 2 does not ordinarily extend beyond the intranet. To connect to the Internet usually requires a router and a modem or other device to connect to an Internet Service Provider’s WAN. These are Layer 3 functions.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Layer 3

Commonly referred to as the routing layer, this layer provides logical partitioning of networks (subnetting), scalability, security, and Quality of Service (QoS).

The backbone of the Internet is built using Layer 3 functions. IP is the premier Layer 3 protocol.

IP is itself, only one protocol in the IP protocol suite. More extensive capabilities are found in the other protocols of the IP suite. For example; the Domain Name System (DNS) associates IP addresses with text names, the Dynamic Host Configuration Protocol (DHCP) eases the administration of IP addresses, and routing protocols such as the Routing Information Protocol (RIP), the Open Shortest Path First (OSPF), and the Border Gateway Protocol (BGP) enable Layer 3 devices to direct data traffic to the intended destination. IP security allows for authentication and encryption. IP not only allows for userto-user communication, but also for transmission from point-to-multipoint (known as IP multicasting).

Layer 4

This layer, known as the transport layer, establishes the communication path between user applications and the network infrastructure and defines the method of communicating. TCP and UDP are well-known protocols in the transport layer. TCP is a “connection-oriented” protocol, and requires the establishment of parameters for transmission prior to the exchange of data. Web technology is based on TCP. UDP is “connectionless” and requires no connection setup. This is important for multicast traffic, which cannot tolerate the overhead and latency of TCP. TCP and UDP also differ in the amount of error recovery provided and whether or not it is visible to the user application. Both TCP and UDP are layered on IP, which has minimal error recovery and detection. TCP forces retransmission of data that was lost by the lower layers, UDP does not.

Layer 7

This layer, known as the application layer, provides access to either the end user application software such as a database. Users communicate with the application, which in turn delivers data to the transport layer. Applications do not usually communicate directly with lower layers. They are written to use a specific communication library, like the popular WinSock library.

Software developers must decide what type of transport mechanism is necessary. For example, Web access requires reliable, error-free access and would demand TCP. Multimedia, on the other hand, requires low overhead and latency and commonly uses UDP.

TCP/IP

The TCP/IP protocol suite is a set of protocols that allow computers to share resources across a network. TCP and IP are only two of the Internet suite of protocols, but they are the best known and it has become common to refer the entire family of Internet protocols as TCP/IP.

TCP/IP is a layered set of protocols. An example, such as sending e-mail, can illustrate this. There is first a protocol for sending and receiving e-mail. This protocol defines a set of commands to identify the sender, the recipient, and the content of the e-mail. The e-mail protocol will not handle the actual communication between the two computers as this is done by TCP/IP. TCP/IP handles the actual sending and receiving of the packets that make up the e-mail exchange.

TCP makes sure the e-mail commands and messages are received by the appropriate computers. It keeps track of what is sent and what is received, and retransmits any packets that are lost or dropped. TCP also handles the division of large messages into several Ethernet packets, and makes sure these packets are received and reassembled in the correct order.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Because these functions are required by a large number of applications, they are grouped into a single protocol, rather than being the part of the specifications for just sending e-mail. TCP is then a library of routines that application software can use when reliable network communications are required.

IP is also a library of routines, but with a more general set of functions. IP handles the routing of packets from the source to the destination. This may require the packets to traverse many different networks. IP can route packets through the necessary gateways and provides the functions required for any user on one network to communicate with any user on another connected network.

The communication interface between TCP and IP is relatively simple. When IP received a packet, it does not know how this packet is related to others it has sent (or received) or even which connection the packet is part of. IP only knows the address of the source and the destination of the packet, and it makes its best effort to deliver the packet to its destination.

The information required for IP to do its job is contained in a series of octets added to the beginning of the packet called headers. A header contains a few octets of data added to the packet by the protocol in order to keep track of it.

Other protocols on other network devices can add and extract their own headers to and from packets as they cross networks. This is analogous to putting data into an envelope and sending the envelope to a higher-level protocol, and having the higher-level protocol put the entire envelope into it’s own, larger envelope. This process is referred to as encapsulation.

Many levels of encapsulation are required for a packet to cross the Internet.

Packet Headers

TCP

Most data transmissions are much longer that a single packet. The data must then be divided up among a series of packets. These packets must be transmitted, received and then reassembled into the original data. TCP handles these functions.

TCP must know how large a packet the network can process. To do this, the TCP protocols at each end of a connection state how large a packet they can handle and the smaller of the two is selected.

The TCP header contains at least 20 octets. The source and destination TCP port numbers are the most important fields. These specify the connection between two TCP protocols on two network devices.

The header also contains a sequence number that is used to ensure the packets are received in the correct order. The packets are not numbered, but rather the octets the packets contain are. If there are 100 octets of data in each packet, the first packet is numbered 0, the second 100, the third 200, etc.

To insure that the data in a packet is received uncorrupted, TCP adds the binary value of all the octets in the packet and writes the sum in the checksum field. The receiving TCP recalculates the checksum and if the numbers are different, the packet is dropped.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 5-13. TCP Packet Header

When packets have been successfully received, TCP sends an acknowledgement. This is simply a packet that has the acknowledgement number field filled in.

An acknowledgement number of 1000 indicates that all of the data up to octet 1000 has been received. If the transmitting TCP does not receive an acknowledgement in a reasonable amount of time, the data is resent.

The window field controls the amount of data being sent at any one time. It would require too much time and overhead to acknowledge each packet received. Each end of the TCP connection declares how much data it is able to receive at any one time by writing this number of octets in the window field.

The transmitting TCP decrements the number in the window field and when it reaches zero, the transmitting TCP stops sending data. When the receiving TCP can accept more data, it increases the number in the window field. In practice, a single packet can acknowledge the receipt of data and give permission for more data to be sent.

TCP sends its packets to IP with the source and destination IP addresses. IP is only concerned with these IP addresses. It is not concerned with the contents of the packet or the TCP header.

IP finds a route for the packet to get to the other end of the TCP connection. IP adds its own header to the packet to accomplish this.

The IP header contains the source and destination addresses, the protocol number, and another checksum.

The protocol number tells the receiving IP which protocol to give the packet to. Although most IP traffic uses TCP, other protocols can be used (such as UDP).

The checksum is used by the receiving IP in the same way as the TCP checksum.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 5-14. IP Packet Header

The flags and fragment offset are used to keep track of packets that must be divided among several smaller packets to cross networks for which they are too large.

The Time-to-Live (TTL) is the number of gateways the packet is allowed to cross between the source and destination. This number is decremented by one when the packet crosses a gateway and when the TTL reaches zero, the packet is dropped. This helps reduce network traffic if a loop develops.

Ethernet

Every active Ethernet device has its own Ethernet address (commonly called the MAC address) assigned to it by the manufacturer. Ethernet uses 48 bit addresses.

The Ethernet header is 14 octets that include the source and destination MAC address and a type code.

There is no relationship between the MAC address of a network node and its IP address. There must be a database of Ethernet addresses and their corresponding IP addresses.

Different protocol families can be in use on the same network. The type code field allows each protocol family to have its own entry.

A checksum is calculated and when the packet is received, the checksum is recalculated. If the two checksums are different, the packet is dropped.

Figure 5-15. Ethernet Packet Header

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

When a packet is received, the headers are removed. The Ethernet Network Interface Card (NIC) removes the Ethernet header and checks the checksum. It then looks at the type code. If the type code is for IP, the packet is given to IP. IP then removes the IP header and looks at its protocol field. If the protocol field is TCP, the packet is sent to TCP. TCP then looks at the sequence number and uses this number and other data from the headers to reassemble the data into the original file.

TCP and UDP Well-Known Ports

Application protocols run ‘on top of’ TCP/IP. When an application wants to send data or a message, it gives the data to TCP. Because TCP and IP take care of the networking details, the application can look at the network connection as a simple data stream.

To transfer a file across a network using the File Transfer Protocol (FTP), a connection must first be established. The computer requesting the file transfer must connect specifically to the FTP server on the computer that has the file.

This is accomplished using sockets. A socket is a pair of TCP port numbers used to establish a connection from one computer to another. TCP uses these port numbers to keep track of connections. Specific port numbers are assigned to applications that wait for requests. These port numbers are referred to as ‘well-known’ ports.

TCP will open a connection to the FTP server using some random port number, 1234 for example, on the local computer. TCP will specify port 21 for the FTP server. Port 21 is the well-known port number for FTP servers. Note that there are two different FTP programs running in this example – an FTP client that requests the file to be transferred, and an FTP server that sends the file to the FTP client. The FTP server accepts commands from the client, so the FTP client must know how to connect to the server (must know the TCP port number) in order to send commands. The FTP Server can use any TCP port number to send the file, so long as it is sent as part of the connection setup.

A TCP connection is then described by a set of four numbers – the IP address and TCP port number for the local computer, and the IP address and TCP port number for the remote computer. The IP address is in the IP header and the TCP port number is in the TCP header.

No two TCP connection can have the same set of numbers, but only one number needs to be different. It is possible, for example, for two users to send files to the same destination at the same time. This could give the following connection numbers:

Internet addresses TCP ports

Connection 1 10.42.73.23, 10.128.12.1 1234, 21

Connection 2 10.42.73.23, 10.128.12.1 1235, 21

The same computers are making the connections, so the IP addresses are the same. Both computers are using the same well-known TCP port for the FTP server. The local FTP clients are using different TCP port numbers.

FTP transfers actually involve two different connections. The connection begins by the FTP sending commands to send a particular file. Once the commands are sent, a second connection is opened for the actual data transfer. Although it is possible to send data on the same connection, it is very convenient for the FTP client to be able to continue to send commands (such as ‘stop sending this file’).

UDP and ICMP

There are many applications that do not require long messages that cannot fit into a single packet. Looking up computer names is an example. Users wanting to make connections to other computers will usually use a name rather than the computer’s IP or MAC address. The user’s computer must be able

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

to determine the remote computer’s address before a connection can be made. A designated computer on the network will contain a database of computer names and their corresponding IP and MAC addresses. The user’s computer will send a query to the name database computer, and the database computer will send a response. Both the query and the response are very short. There is no need to divide the query or response between multiple packets, so the complexity of TCP is not required. If there is no response to the query after a period of time, the query can simply be resent.

The User Datagram Protocol (UDP) is designed for communications that do not require division among multiple packets and subsequent reassembly. UDP does not keep track of what is sent.

UDP uses port numbers in a way that is directly analogous to TCP. There are well-known UDP port numbers for servers that use UDP.

Figure 5-16. Ethernet Packet Header

The UDP header is shorter than a TCP header. UDP also uses a checksum to verify that data is received uncorrupted.

The Internet Control Message Protocol (ICMP) is also a simplified protocol used for error messages and messages used by TCP/IP. ICMP, like UDP, processes messages that will fit into a single packet. ICMP does not, however use ports because its messages are processed by the network software.

The Domain Name System

Computer users usually prefer to use text names for computers they may want to open a connection with. Computers themselves, require 32 bit IP addresses. Somewhere, a database of network devices’ text names and their corresponding IP addresses must be maintained.

The Domain Name System (DNS) is used to map names to IP addresses throughout the Internet and has been adapted for use within intranets.

For two DNS servers to communicate across different subnets, the DNS Relay of the DES-3326 must be used. The DNS servers are identified by IP addresses.

Mapping Domain Names to Addresses

Name-to-address translation is performed by a program called a Name server. The client program is called a Name resolver. A Name resolver may need to contact several Name servers to translate a name to an address.

The Domain Name System (DNS) servers are organized in a somewhat hierarchical fashion. A single server often holds names for a single network, which is connected to a root DNS server – usually maintained by an ISP.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Domain Name Resolution

The domain name system can be used by contacting the name servers one at a time, or by asking the domain name system to do the complete name translation. The client makes a query containing the name, the type of answer required, and a code specifying whether the domain name system should do the entire name translation, or simply return the address of the next DNS server if the server receiving the query cannot resolve the name.

When a DNS server receives a query, it checks to see if the name is in its subdomain. If it is, the server translates the name and appends the answer to the query, and sends it back to the client. If the DNS server cannot translate the name, it determines what type of name resolution the client requested. A complete translation is called recursive resolution and requires the server to contact other DNS servers until the name is resolved. Iterative resolution specifies that if the DNS server cannot supply an answer, it returns the address of the next DNS server the client should contact.

Each client must be able to contact at least one DNS server, and each DNS server must be able to contact at least one root server.

The address of the machine that supplies domain name service is often supplied by a DHCP or BOOTP server, or can be entered manually and configured into the operating system at startup.

DHCP Servers

The Dynamic Host Configuration Protocol (DHCP) is used to dynamically assign a TCP/IP network configuration to network devices and computers on the network. It also ensures that IP address conflicts do not occur.

IP addresses are assigned from a pool of free addresses. Each IP address assigned has a ‘lease’ and a ‘lease expiration period’. The lease must be periodically renewed. If the lease is expires, the IP address is returned to the pool of available IP addresses.

Usually, it is a network policy to assign the same IP address to a given network device or computer each time.

If the IP address lease expires, the network device sends a message to the DHCP server requesting a lease renewal. The DHCP server can send an acknowledgement containing a new lease and updated configuration information.

If an IP address lease cannot be renewed, the network device or computer sends a request to all local DHCP servers attempting to renew the lease. If the DHCP returns a negative acknowledgement, the network device must release its TCP/IP configuration and reinitialize.

When a new TCP/IP configuration is received from a DHCP server, the network device checks for a possible IP address conflict by sending an Address Resolution Protocol (ARP) request that contains its new IP address.

For two DHCP servers to communicate across different subnets, the BOOTP/DHCP Relay of the DES-3326 must be used. The DHCP servers are identified by IP addresses.

IP Routing

IP handles the task of determining how packets will get from their source to their destination. This process is referred to as routing.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

For IP to work, the local system must be attached to a network. It is safe to assume that any system on this network can send packets to any other system, but when packets must cross other networks to reach a destination on a remote network, these packets must be handled by gateways (also called routers).

Gateways connect a network with one or more other networks. Gateways can be a computer with two network interfaces or a specialized device with multiple network interfaces. The device is designed to forward packets from one network to another.

IP routing is based on the network address of the destination IP address. Each computer has a table of network addresses. For each network address, a corresponding gateway is listed. This is the gateway to use to communicate with that network. The gateway does not have to be directly connected to the remote network, it simply needs to be the first place to go on the way to the remote network.

Before a local computer sends a packet, it first determines whether the destination address is on the local network. If it is, the packet can be sent directly to the remote device. If it is not, the local computer looks for the network address of the destination and the corresponding gateway address. The packet is then sent to the gateway leading to the remote network. There is often only one gateway on a network.

A single gateway is usually defined as a default gateway, if that gateway connects the local network to a backbone network or to the Internet. This default gateway is also used whenever no specific route is found for a packet, or when there are several gateways on a network.

Local computers can use default gateways, but the gateways themselves need a more complete routing table to be able to forward packets correctly. A protocol is required for the gateways to be able to communicate between themselves and to keep their routing tables updated.

Packet Fragmentation and Reassembly

TCP/IP can be used with many different types of networks, but not all network types can handle the same length packets.

When IP is transmitting large files, large packets are much more efficient than small ones. It is preferable to use the largest possible packet size, but still be able to cross networks that require smaller packets.

To do this, IP can ‘negotiate’ packet size between the local and remote ends of a connection. When an IP connection is first made, the IPs at both ends of the connection state the largest packet they can handle. The smaller of the two is selected.

When an IP connection crosses multiple networks, it is possible that one of the intermediate networks has a smaller packet size limit than the local or remote network. IP is not able to determine the maximum packet size across all of the networks that may make up the route for a connection. IP has, therefore, a method to divide packets into multiple, smaller packets to cross such networks. This division of large packets into smaller packets is referred to as fragmentation.

A field in the TCP header indicates that a packet has been fragmented, and other information aids in the reassembly of the packets into the original data.

Gateways that connect networks of different packet size limits split the large packets into smaller ones and forward the smaller packets on their attached networks.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

ARP

The Address Resolution Protocol (ARP) determines the MAC address and IP address correspondence for a network device.

A local computer will maintain an ARP cache that is a table of MAC addresses and the corresponding IP addresses. Before a connection with another computer is made, the local computer first checks its ARP cache to determine whether the remote computer has an entry. If it does, the local computer reads the remote computer’s MAC address and writes it into the destination field of the packets to be sent.

If the remote computer does not have an ARP cache entry, the local computer must send an ARP request and wait for a reply.

When the local computer receives the ARP reply packet, the local ARP reads the IP MAC address pair, and then checks the ARP cache for this entry. If there is an entry, it is updated with the new information. If there is no entry, a new entry is made.

There are two possible cases when an ARP packet is received by a local computer. First, the local computer is the target of the request. If it is, the local ARP replies by sending its MAC IP address pair back to the requesting system. Second, if the local computer is not the target of the request, the packet is dropped.

Multicasting

Multicasting is a group of protocols and tools that enable a single source point to send packets to groups of multiple destination points with persistent connections that last for some amount of time. The main advantage to multicasting is a decrease in the network load compared to broadcasting.

Multicast Groups

Class D IP addresses are assigned to a group of network devices that comprise a multicast group. The four most significant four bits of a Class D address are set to “1110”. The following 28 bits is referred to as the ‘multicast group ID’. Some of the range of Class D addresses are registered with the Internet Assigned Numbers Authority (IANA) for special purposes. For example, the block of multicast addresses ranging from 224.0.0.1 to 224.0.0.225 is reserved for use by routing protocols and some other low-level topology discovery and maintenance protocols.

Figure 5-17. Class D Multicast Address

Some of the reserved IP multicast addresses are as follows:

Address Assignment

224.0.0.0

224.0.0.1

Base Address (reserved)

All Systems on this subnet

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

224.0.0.2

224.0.0.3

224.0.0.4

224.0.0.5

224.0.0.6

224.0.0.7

224.0.0.8

224.0.0.9

224.0.0.10

224.0.0.11

224.0.0.12

224.0.0.13

224.0.0.14

224.0.0.15

All Routers on this subnet

Unassigned

DVMRP Routers

OSPF IGP Routers

OSPF IGP Designated Routers

ST Routers

ST Hosts

All RIP2 Routers

All IGRP Routers

Mobile Agents

DHCP Servers and Relay Agents

All PIM Routers

RSVP Encapsulation

All CBT Routers

224.0.0.16

224.0.0.17

224.0.0.18

224.0.0.19

Designated Sbm

All Sbms

VRRP

Unassigned

through

224.0.0.225

224.0.0.21

DVMRP on MOSPF

Table 5-10. Reserved Multicast Address Assignment

Internet Group Management Protocol (IGMP)

End users that want to receive multicast packets must be able to inform nearby routers that they want to become a multicast group member of the group these packets are being sent to. The Internet Group Management Protocol (IGMP) is used by multicast routers to maintain multicast group membership. IGMP is also used to coordinate between multiple multicast routers that may be present on a network by electing one of the multicast routers as the ‘querier’. This router then keep track of the membership of multicast groups that have active members on the network. IGMP is used to determine whether the router should forward multicast packets it receives to the subnetworks it is attached to or not. A multicast router that has received a multicast packet will check to determine if there is at least one member of a multicast group that has requested to receive multicast packets from this source. If there is one member, the packet is forwarded. If there are no members, the packet is dropped.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

IGMP Versions 1 and 2

Users that want to receive multicast packets need to be able to join and leave multicast groups. This is accomplished using IGMP.

Figure 5-18. IGMP Message Format

The IGMP Type codes are shown below:

Type Meaning

0x11

0x11 Specific Group Membership Query (if Group Address

0x16 Membership Report (version 2)

Membership Query (if Group Address is 0.0.0.0)

is Present)

0x17 Leave a Group (version 2)

0x12 Membership Report (version 1)

Table 5-11. IGMP Type Codes

Multicast routers use IGMP to manage multicast group memberships:

• An IGMP “report” is sent by a user’s computer to join a group

• IGMP version 1 does not have an explicit ‘leave’ message. Group members have an expiration

timer, and if this timer expires before a query response is returned, the member is dropped from the group.

• IGMP version 2 introduces an explicit “leave” report. When a user wants to leave a group, this report is sent to the multicast router (for IGMP version 2).

• Multicast routers send IGMP queries (to the all-hosts group address: 224.0.0.1) periodically to see whether any group members exist on their subnetworks. If there is no response from a particular group, the router assumes that there are no group members on the network, and multicast packets are not forwarded.

The TTL field of query messages is set to 1 so that the queries do not get forwarded to other subnetworks.

IGMP version 2 introduces a few extensions to IGMP version 1 such as, the election of a single multicast querier for each network, explicit ‘leave’ reports, and queries that are specific to a particular multicast group.

The router with the lowest IP address is elected as the querier. The explicit group leave message is added to decrease latency, and routers can ask for membership reports from a particular multicast group ID.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The transition states a host will go through to join or leave a multicast group are shown in the diagram below.

Figure 5-19. IGMP State Transitions

Multicast Routing Algorithms

An algorithm is not a program. An algorithm is a statement of how a problem can be solved. A program is written to implement an algorithm.

Multicast packets are delivered by constructing multicast trees where the multicast router is the trunk, the branches are the various subnetworks that may be present, and the leaves are end recipients of the multicast packets. Several algorithms have been developed to construct these trees and to prune branches that have no active mulitcast group members.

Flooding

The simplest algorithm for the delivery of multicast packets is for the multicast router to forward a multicast packet to all interfaces. This is referred to as flooding. An equally simple refinement of flooding is to have the router check to determine if a given multicast packet has been received before (in a certain amount of time). If it has, then the packet does not need to be forwarded at all and can be dropped. If the packet is being received for the first time, it should be flooded to all interfaces, except the interface on which it was received. This will ensure that all routers on the network will receive at least one copy of the multicast packet.

There are some obvious disadvantages to this simple algorithm. Flooding duplicates a lot of packets and uses a lot of network bandwidth. A multicast router must also keep a record of the multicast packets it has received (for a period of time) to determine if a given packet has been previously received. So flooding uses a lot of router memory.

Multicast Spanning Trees

A multicast delivery tree that spans the entire network with a single active link between routers (or subnetwork) is called a multicast spanning tree. Links (or branches) are chosen such that there is only one active path between any two routers. When a router receives a multicast packet, it forwards the

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

packet on all links except the one on which it was received. This guarantees that all routers in the network will receive a copy of the packet. The only information the router needs to store is whether a link is a part of the spanning tree (leads to a router) or not.

Multicast spanning trees do not use group membership information when deciding to forward or drop a given multicast packet.

Reverse Path Broadcasting (RPB)

The Reverse Path Broadcasting (RPB) algorithm is an enhancement of the multicast spanning tree algorithm. RPB constructs a spanning tree for each multicast source. When the router receives a multicast packet, it then checks to determine if the packet was received on the shortest path back from the router to the source. If the packet was received on the shortest path back to the source, the packet is forwarded on all links except the link on which the packet was received. If the packet was not received on the shortest link back to the source, the packet is dropped.

If a link-state routing protocol is in use, RPB on a local router can determine if the path from the source through the local router to an immediately neighboring router. If it is not, the packet will be dropped at the next router and the packet should not be forwarded.

If a distance-vector routing protocol is in use, a neighboring router can either advertise its previous hop for the source as part of its routing update messages. This will ‘poison-reverse’ the route (or have the local router prune the branch from the multicast source to the neighboring router because the neighboring router has a better route from the source to the next router or subnetwork).

Since multicast packets are forwarded through the shortest route between source and destination, RPB is fast. A given router also does not need information about the entire spanning tree, nor does it need a mechanism to stop the forwarding of packets.

RPB does not use multicast group membership information in its forwarding decisions.

Reverse Path Multicasting (RPM)

Reverse Path Multicasting (RPM) introduces an enhancement to RPB – an explicit method to prune branches of the spanning tree that have on active multicast group members for the source. RPM constructs a tree that spans only subnetworks with multicast group member and routers along the shortest path between the source and the destinations.

When a multicast router receives a multicast packet, it is forwarded using the RPB constructed spanning tree. Subsequent routers in the tree that have no active path to another router are referred to as leaf routers. If the multicast packet if forwarded to a leaf router that has no active multicast group members for the source, the leaf router will send a prune message to the previous router. This will remove the leaf router’s branch from the spanning tree, and no more multicast packets (from that source) will be forwarded to it. Prune messages have a TTL equal to one, so they can be sent only one hop (one router) back toward the source. If the previous router receives prune messages from all of its branch and leaf routers, the previous router will then send it’s own prune message back one router toward the multicast source, and the process will repeat. In this way, multicast group membership information can be used to prune the spanning tree between a given multicast source and the corresponding multicast group.

Since the membership of any given multicast group can change and the network topology can also change, RPM periodically removes all of the prune information it has gathered from its memory, and the entire process repeats. This gives all subsequent routers on the network a chance to receive multicast packets from all multicast sources on the network. It also gives all users a chance to join a given multicast group.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Multicast Routing Protocols

This section contains an overview of two multicast routing protocols – Distance Vector Multicast Routing Protocol (DVMRP), and Protocol Independent Multicast-Dense Mode

(PIM-DM). The most commonly used routing protocol (not a multicast routing protocol), the Routing Information Protocol, is discussed in a later section.

Distance Vector Multicast Routing Protocol (DVMRP)

The Distance Vector Multicast Routing Protocol (DVMRP) was derived from the Routing Information Protocol (RIP) with the introduction of multicast delivery trees constructed from information about the ‘distance’ from the local router back toward the multicast source. DVMRP uses an RPM algorithm to construct its multicast delivery trees.

The first multicast packet received by a multicast router using DVMRP is flooded to all interfaces except the one on which the packet was received. Subsequent prune messages are used to prune branches of the delivery tree that are either not on the shortest path back to the multicast source, or that have no active multicast group members. A ‘graft’ message is added that allows a previously pruned branch of the multicast delivery tree to be reactivated. This allows for lower latency when a leaf router adds a new member to a multicast membership group. Graft messages are forwarded one hop (one router) back at a time toward a multicast source until they reach a router that is on an active branch of the multicast delivery tree.

If there is more than one multicast router on a network, the one that has the shortest path back to the multicast source is elected to forward multicast packets from that source. All other routers will discard multicast packets from that source. If two multicast routers on a network have the same distance back to a multicast source, the router with the lowest IP address is elected.

DVMRP also supports tunnel interfaces, where two multicast routers are connected through a router that cannot process multicast packets. This allows multicast packets to cross networks with routers that are not multicast-aware.

Protocol-Independent Multicast – Dense Mode

There are two protocols in Protocol Independent Multicast (PIM), Protocol Independent Multicast-Dense Mode (PIM-DM) which is used when the multicast destinations are closely spaced, and Protocol Independent Multicast-Sparse Mode (PIM-SM) which is used when the multicast destinations are spaced further apart. PIM-DM is most commonly implemented in an intranetwork (LAN) where the distance between users is minimal.

Routing Protocols

Routing Information Protocol (RIP)

The Routing Information Protocol is a distance-vector routing protocol. There are two types of network devices running RIP – active and passive. Active devices advertise their routes to others through RIP messages, while passive devices listen to these messages. Both active and passive routers update their routing tables based upon RIP messages that active routers exchange. Only routers can run RIP in the active mode.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Every 30 seconds, a router running RIP broadcasts a routing update containing a set of pairs of network addresses and a distance (represented by the number of hops or routers between the advertising router and the remote network). So, the vector is the network address and the distance is measured by the number of routers between the local router and the remote network.

RIP measures distance by an integer count of the number of hops from one network to another. A router is one hop from a directly connected network, two hops from a network that can be reached through a router, etc. The more routers between a source and a destination, the greater the RIP distance (or hop count).

There are a few rules to the routing table update process that help to improve performance and stability. A router will not replace a route with a newly learned one if the new route has the same hop count (sometimes referred to as ‘cost’). So learned routes are retained until a new route with a lower hop count is learned.

When learned routes are entered into the routing table, a timer is started. This timer is restarted every time this route is advertised. If the route is not advertised for a period of time (usually 180 seconds), the route is removed from the routing table.

RIP does not have an explicit method to detect routing loops. Many RIP implementations include an authorization mechanism (a password) to prevent a router from learning erroneous routes from unauthorized routers.

To maximize stability, the hop count RIP uses to measure distance must have a low maximum value. Infinity (that is, the network is unreachable) is defined as 16 hops. In other words, if a network is more than 16 routers from the source, the local router will consider the network unreachable.

RIP can also be slow to converge (to remove inconsistent, unreachable or looped routes from the routing table) because RIP messages propagate relatively slowly through a network.

Slow convergence can be solved by using split horizon update, where a router does not propagate information about a route back to the interface on which it was received. This reduces the probability of forming transient routing loops.

Hold down can be used to force a router to ignore new route updates for a period of time (usually 60 seconds) after a new route update has been received. This allows all routers on the network to receive the message.

A router can ‘poison reverse’ a route by adding an infinite (16) hop count to a route’s advertisement. This is usually used in conjunction with triggered updates, which force a router to send an immediate broadcast when an update of an unreachable network is received.

RIP Version 1 Message Format

There are two types of RIP messages: routing information messages and information requests. The same format is used by both types.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 5-20. RIP v.1 Message Format

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The COMMAND field specifies an operation according the following table:

Command Meaning

Request for partial or full routing information

Response containing network-distance pairs from sender’s routing table

Turn on trace mode (obsolete)

Turn off trace mode (obsolete)

Reserved for Sun Microsystem’s internal use

Update Request

Update Response

Update Acknowledgement

Table 5-12. RIP Command Codes

The field VERSION contains the protocol version number (1 in this case), and is used by the receiver to verify which version of RIP the packet was sent from.

RIP 1 Message

RIP is not limited to TCP/IP. Its address format can support up to 14 octets (when using IP, the remaining 10 octets must be zeros). Other network protocol suites can be specified in the Family of Source Network field (IP has a value of 2). This will determine how the address field is interpreted.

RIP specifies that the IP address 0.0.0.0 denotes a default route.

The distances, measured in router hops are entered in the Distance to Source Network, and Distance to Destination Network fields.

RIP 1 Route Interpretation

RIP was designed to be used with classed address schemes, and does not include an explicit subnet mask. An extension to version 1 does allow routers to exchange subnetted addresses, but only if the subnet mask used by the network is the same as the subnet mask used by the address. This means the RIP version 1 cannot be used to propagate classless addresses.

Routers running RIP version 1 must send different update messages for each IP interface to which it is connected. Interfaces that use the same subnet mask as the router’s network can contain subnetted routes, other interfaces cannot. The router will then advertise only a single route to the network.

RIP Version 2 Extensions

RIP version 2 includes an explicit subnet mask entry, so RIP version 2 can be used to propagate variable length subnet addresses or CIDR classless addresses. RIP version 2 also adds an explicit next hop entry, which speeds convergence and helps prevent the formation of routing loops.

RIP2 Message Format

The message format used with RIP2 is an extension of the RIP1 format:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 5-21. RIP Message Format

RIP version 2 also adds a 16-bit route tag that is retained and sent with router updates. It can be used to identify the origin of the route.

Because the version number in RIP2 occupies the same octet as in RIP1, both versions of the protocols can be used on a given router simultaneously without interference.

Open Shortest Path First (OSPF)

The Open Shortest Path First (OSPF) routing protocol uses a link-state algorithm to determine routes to network destinations. A “link” is an interface on a router and the “state” is a description of that interface and its relationship to neighboring routers. The state contains information such as the IP address, subnet mask, type of network the interface is attached to, other routers attached to the network, etc. The collection of link-states is then collected in a link-state database that is maintained by routers running OSPF.

OSPF specifies how routers will communicate to maintain their link-state database and defines several concepts about the topology of networks that use OSPF.

To limit the extent of link-state update traffic between routers, OSPF defines the concept of Area. All routers within an area share the exact same link-state database, and a change to this database on one router triggers an update to the link-state database of all other routers in that area. Routers that have interfaces connected to more than one area are called Border Routers and take the responsibility of distributing routing information between areas.

One area is defined as Area 0 or the Backbone. This area is central to the rest of the network in that all other areas have a connection (through a router) to the backbone. Only routers have connections to the backbone and OSPF is structured such that routing information changes in other areas will be introduced into the backbone, and then propagated to the rest of the network.

When constructing a network to use OSPF, it is generally advisable to begin with the backbone (area 0) and work outward.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The Link-State Algorithm

An OSPF router uses a link-state algorithm to build a shortest path tree to all destinations known to the router. The following is a simplified description of the algorithm’s steps:

1. When OSPF is started, or when a change in the routing information changes, the router generates a link-state advertisement. This advertisement is a specially formatted packet that contains information about all the link-states on the router.

2. This link-state advertisement is flooded to all router in the area. Each router that receives the link-state advertisement will store the advertisement and then forward a copy to other routers.

3. When the link-state database of each router is updated, the individual routers will calculate a Shortest Path Tree to all destinations − with the individual router as the root. The IP routing table will then be made up of the destination address, associated cost, and the address of the next hop to reach each destination.

4. Once the link-state databases are updated, Shortest Path Trees calculated, and the IP routing tables written − if there are no subsequent changes in the OSPF network (such as a network link going down) there is very little OSPF traffic.

The Shortest Path Algorithm

The Shortest Path to a destination is calculated using the Dijkstra algorithm. Each router is places at the root of a tree and then calculates the shortest path to each destination based on the cumulative cost to reach that destination over multiple possible routes. Each router will then have its own Shortest Path Tree (from the perspective of its location in the network area) even though every router in the area will have and use the exact same link-state database.

The following sections describe the information used to build the Shortest Path Tree.

OSPF Cost

Each OSPF interface has an associated cost (also called “metric”) that is representative of the overhead required to send packets over that interface. This cost is inversely proportional to the bandwidth of the interface (i.e. a higher bandwidth interface has a lower cost). There is then a higher cost (and longer time delays) in sending packets over a 56 Kbps dial-up connection than over a 10 Mbps Ethernet connection. The formula used to calculate the OSPF cost is as follows:

Cost = 100,000,000 / bandwidth in bps

As an example, the cost of a 10 Mbps Ethernet line will be 10 and the cost to cross a 1.544 Mbps T1 line will be 64.

Shortest Path Tree

To build Router A’s shortest path tree for the network diagramed below, Router A is put at the root of the tree and the smallest cost link to each destination network is calculated.

192.128.11.0

Router C

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Router A

128.213.0.0

Router B

Router D

222.211.10.0

Figure 5-22. Constructing a Shortest Path Tree

Router A

128.213.0.0

Router B

192.213.11.0

Router D

222.211.10.0

Figure 5-23. Constructing a Shortest Path Tree

Router C

The diagram above shows the network from the viewpoint of Router A. Router A can reach

192.213.11.0 through Router B with a cost of 10+5=15. Router A can reach 222.211.10.0 through Router C with a cost of 10+10=20. Router A can also reach 222.211.10.0 through Router B and Router D with a cost of 10+5+10=25, but the cost is higher than the route through Router C. This higher-cost route will not be included in the Router A’s shortest path tree. The resulting tree will look like this:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

128.213.0.0

Router A

Router B

192.213.11.0

Figure 5-24. Constructing a Shortest Path Tree - Completed

Note that this shortest path tree is only from the viewpoint of Router A. The cost of the link from Router B to Router A, for instance is not important to constructing Router A’s shortest path tree, but is very important when Router B is constructing its shortest path tree.

Note also that directly connected networks are reached at a cost of 0, while other networks are reached at the cost calculated in the shortest path tree.

Router A can now build its routing table using the network addresses and costs calculated in building the above shortest path tree.

Router C

222.211.10.0

Areas and Border Routers

OSPF link-state updates are forwarded to other routers by flooding to all routers on the network. OSPF uses the concept of areas to define where on the network routers that need to receive particular linkstate updates are located. This helps ensure that routing updates are not flooded throughout the entire network and to reduce the amount of bandwidth consumed by updating the various router’s routing tables.

Areas establish boundaries beyond which link-state updates do not need to be flooded. So the exchange of link-state updates and the calculation of the shortest path tree are limited to the area that the router is connected to.

Routers that have connections to more than one area are called Border Routers (BR). The Border Routers have the responsibility of distributing necessary routing information and changes between areas.

Areas are specific to the router interface. A router that has all of its interfaces in the same area is called an Internal Router. A router that has interfaces in multiple areas is called a Border Router. Routers that act as gateways to other networks (possibly using other routing protocols) are called Autonomous System Border Routers (ASBRs).

Link-State Packets

There are different types of link-state packets, four are illustrated below:

• Router Link-State Updates − these describe a router’s links to destinations within an area.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Summary Link-State Updates – issued by Border Routers and describe links to networks outside the area but within the Autonomous System (AS).

• Network Link-State Updates – issued by multi-access areas that have more than one attached router. One router is elected as the Designated Router (DR) and this router issues the network link-state updates describing every router on the segment.

• External Link-State Updates – issued by an Autonomous System Border Router and describes routes to destinations outside the AS or a default route to the outside AS.

The format of these link-state updates is described in more detail below.

Router link-state updates are flooded to all routers in the current area. These updates describe the destinations reachable through all of the router’s interfaces.

Summary link-state updates are generated by Border Routers to distribute routing information about other networks within the AS. Normally, all Summary link-state updates are forwarded to the backbone (area 0) and are then forwarded to all other areas in the network. Border Routers also have the responsibility of distributing routing information from the Autonomous System Border Router in order for routers in the network to get and maintain routes to other Autonomous Systems.

Network link-state updates are generated by a router elected as the Designated Router on a multiaccess segment (with more than one attached router). These updates describe all of the routers on the segment and their network connections.

External link-state updates carry routing information to networks outside the Autonomous System. The Autonomous System Border Router is responsible for generating and distributing these updates.

OSPF Authentication

OSPF packets can be authenticated as coming from trusted routers by the use of predefined passwords. The default for routers is to use not authentication.

There are two other authentication methods − simple password authentication (key) and Message Digest authentication (MD-5).

Simple Password Authentication

A password (or key) can be configured on a per-area basis. Routers in the same area that participate in the routing domain must be configured with the same key. This method is possibly vulnerable to passive attacks where a link analyzer is used to obtain the password.

Message Digest Authentication (MD-5)

MD-5 authentication is a cryptographic method. A key and a key-ID are configured on each router. The router then uses an algorithm to generate a mathematical “message digest” that is derived from the OSPF packet, the key and the key-ID. This message digest (a number) is then appended to the packet. The key is not exchanged over the wire and a non-decreasing sequence number is included to prevent replay attacks.

The Backbone and Area 0

OSPF limits the number of link-state updates required between routers by defining areas within which a given router operates. When more than one area is configured, one area is designated as area 0 − also called the backbone.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The backbone is at the center of all other areas − all areas of the network have a physical (or virtual) connection to the backbone through a router. OSPF allows routing information to be distributed by forwarding it into area 0, from which the information can be forwarded to all other areas (and all other routers) on the network.

In situations where an area is required, but is not possible to provide a physical connection to the backbone, a virtual link can be configured.

Virtual Links

Virtual links accomplish two purposes:

1. Linking an area that does not have a physical connection to the backbone.

2. Patching the backbone in case there is a discontinuity in area 0.

Areas Not Physically Connected to Area 0

All areas of an OSPF network should have a physical connection to the backbone, but is some cases it is not possible to physically connect a remote area to the backbone. In these cases, a virtual link is configured to connect the remote area to the backbone. A virtual path is a logical path between two border routers that have a common area, with one border router connected to the backbone.

Partitioning the Backbone

OSPF also allows virtual links to be configured to connect the parts of the backbone that are discontinuous. This is the equivalent to linking different area 0s together using a logical path between each area 0. Virtual links can also be added for redundancy to protect against a router failure. A virtual link is configured between two border routers that both have a connection to their respective area 0s.

Neighbors

Routers that are connected to the same area or segment become neighbors in that area. Neighbors are elected via the Hello protocol. IP multicast is used to send out Hello packets to other routers on the segment. Routers become neighbors when they see themselves listed in a Hello packet sent by another router on the same segment. In this way, two-way communication is guaranteed to be possible between any two neighbor routers.

Any two routers must meet the following conditions before the become neighbors:

• Area ID − two routers having a common segment − their interfaces have to belong to the same area on that segment. Of course, the interfaces should belong to the same subnet and have the same subnet mask.

• Authentication − OSPF allows for the configuration of a password for a specific area. Two routers on the same segment and belonging to the same area must also have the same OSPF password before they can become neighbors.

• Hello and Dead Intervals − The Hello interval specifies the length of time, in seconds, between the hello packets that a router sends on an OSPF interface. The dead interval is the number of seconds that a router’s Hello packets have not been seen before its neighbors declare the OSPF router down. OSPF routers exchange Hello packets on each segment in order to acknowledge each other’s existence on a segment and to elect a Designated Router on multi-access segments. OSPF requires these intervals to be exactly the same between any two neighbors. If any of these intervals are different, these routers will not become neighbors on a particular segment.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

• Stub Area Flag − any two routers also have to have the same stub area flag in their Hello packets in order to become neighbors.

Adjacencies

Adjacent routers go beyond the simple Hello exchange and participate in the link-state database exchange process. OSPF elects one router as the Designated Router (DR) and a second router as the Backup Designated Router (BDR) on each multi-access segment (the BDR is a backup in case of a DR failure). All other routers on the segment will then contact the DR for link-state database updates and exchanges. This limits the bandwidth required for link-state database updates.

Designated Router Election

The election of the DR and BDR is accomplished using the Hello protocol. The router with the highest OSPF priority on a given multi-access segment will be elected the DR for that segment. In case of a tie, the router with the highest Router ID wins. The default OSPF priority is 1. A priority of zero indicates a router that cannot be elected as the DR.

Building Adjacency

Two routers undergo a multi-step process in building the adjacency relationship. The following is a simplified description of the steps required:

• Down − No information has been received from any router on the segment.

• Attempt − On non-broadcast multi-access networks (such as Frame Relay or X.25), this

state indicates that no recent information has been received from the neighbor. An effort should be made to contact the neighbor by sending Hello packets at the reduced rate set by the Poll Interval.

• Init − The interface has detected a Hello packet coming from a neighbor but bi- directional communication has not yet been established.

• Two-way − Bi-directional communication with a neighbor has been established. The router has seen its address in the Hello packets coming from a neighbor. At the end of this stage the DR and BDR election would have been done. At the end of the Two-way stage, routers will decide whether to proceed in building an adjacency or not. The decision is based on whether one of the routers is a DR or a BDR or the link is a pointto-point or virtual link.

• Exstart − (Exchange Start) Routers establish the initial sequence number that is going to be used in the information exchange packets. The sequence number insures that routers always get the most recent information. One router will become the primary and the other will become secondary. The primary router will poll the secondary for information.

• Exchange − Routers will describe their entire link-state database by sending database description packets.

• Loading − The routers are finalizing the information exchange. Routers have link-state request list and a link-state retransmission list. Any information that looks incomplete or outdated will be put on the request list. Any update that is sent will be put on the retransmission list until it gets acknowledged.

• Full − The adjacency is now complete. The neighboring routers are fully adjacent. Adjacent routers will have the same link-state database.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Adjacencies on Point-to-Point Interfaces

OSPF Routers that are linked using point-to-point interfaces (such as serial links) will always form adjacencies. The concepts of DR and BDR are unnecessary.

OSPF Packet Formats

All OSPF packet types begin with a standard 24-byte header and there are five packet types. The header is described first, and each packet type is described in a subsequent section.

All OSPF packets (except for Hello packets) forward link-state advertisements. Link-State Update packets, for example, flood advertisements throughout the OSPF routing domain.

• OSPF packet header

• Hello packet

• Database Description packet

• Link-State Request packet

• The Link-State Update packet

• Link-State Acknowledgment packet

The OSPF Packet Header

Every OSPF packet is preceded by a common 24-byte header. This header contains the information necessary for a receiving router to determine if the packet should be accepted for further processing.

The format of the OSPP packet header is shown below:

OSPF Packet Header

Version No.

Checksum

Type

Router ID

Area ID

Authentication

Auth entication

Figure 5-25. OSPF Packet Header

Packet Length

Authentication Type

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Field Description

Version No. The OSPF version number

Type The OSPF packet type. The OSPF packet types

are as follows:

Type Description

1 Hello

2 Database Description

3 Link-State Request

4 Link-State Update

5 Link-State Acknowledgment

Packet Length The length of the packet in bytes. This length

includes the 24-byte header.

Router ID The Router ID of the packet’s source.

Area ID A 32-bit number identifying the area that this

packet belongs to. All OSPF packets are associated with a single area. Packets traversing a virtual link are assigned the backbone Area ID of

0.0.0.0

Checksum A standard IP checksum that includes all of the

packet’s contents except for the 64-bit authentication field.

Authentication Type The type of authentication to be used for the

packet.

Authentication A 64-bit field used by the authentication scheme.

Table 5-13. OSPF Packet Header

The Hello Packet

Hello packets are OSPF packet type 1. They are sent periodically on all interfaces, including virtual links, in order to establish and maintain neighbor relationships. In addition, Hello Packets are multicast on those physical networks having a multicast or broadcast capability, enabling dynamic discovery of neighboring routers.

All routers connected to a common network must agree on certain parameters such as the Network Mask, the Hello Interval, and the Router Dead Interval. These parameters are included in hello packets, so that differences can inhibit the forming of neighbor relationships. A detailed explanation of the receive processing for Hello packets, so that differences can inhibit the forming of neighbor relationships.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The format of the Hello packet is shown below:

Hello Packet

Version No.

Checksum Authentication Type

Hello Interval

Router ID

Area ID

Authentication

Network Mask

Options Router Priority

Router Dead Interval

Designated Router

Backup Designated Router

Neighbor

Packet Length

Figure 5-26. Hello Packet

Field Description

Network Mask The network mask associated with this interface.

Options The optional capabilities supported by the router.

Hello Interval The number of seconds between this router’s Hello

packets.

Router Priority This router’s Router Priority. The Router Priority is

used in the election of the DR and BDR. If this field is set to 0, the router is ineligible to become the DR or the BDR.

Router Dead Interval The number of seconds that must pass before

declaring a silent router as down.

Designated Router The identity of the DR for this network, in the view of

the advertising router. The DR is identified here by its IP interface address on the network.

Backup Designated Router The identity of the Backup Designated Router (BDR)

for this network. The BDR is identified here by its IP interface address on the network. This field is set to

0.0.0.0 if there is no BDR.

Neighbor The Router Ids of each router from whom valid Hello

packets have been seen within the Router Dead Interval on the network.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Table 5-14. Hello Packet

The Database Description Packet

Database Description packets are OSPF packet type 2. These packets are exchanged when an adjacency is being initialized. They describe the contents of the topological database. Multiple packets may be used to describe the database. For this purpose a poll-response procedure is used. One of the routers is designated to be master, the other a slave. The master seconds Database Description packets (polls) that are acknowledged by Database Description packets sent by the slave (responses). The responses are linked to the polls via the packets’ DD sequence numbers.

Database Description Packet

Version No.

Reserved

Checksum

2 Packet Length

Router ID

Area ID

Authentication

Reserved

DD Sequence No.

Link-State Advertisement Header ...

Authentication Type

Figure 5-27. Database Description Packet

Field Description

Options The optional capabilities supported by the router.

I – bit The Initial bit. When set to 1, this packet is the

first in the sequence of Database Description packets.

M – bit The More bit. When set to 1, this indicates that

more Database Description packets will follow.

Options

MS – bit The Master Slave bit. When set to 1, this indicates

that the router is the master during the Database Exchange process. A zero indicates the opposite.

DD Sequence Number User to sequence the collection of Database

Description Packets. The initial value (indicated by the Initial bit being set) should be unique. The DD sequence number then increments until the complete database description has been sent.

Table 5-15. Database Description Packet

The rest of the packet consists of a list of the topological database’s pieces. Each link state advertisement in the database is described by its link state advertisement header.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The Link-State Request Packet

Link-State Request packets are OSPF packet type 3. After exchanging Database Description packets with a neighboring router, a router may find that parts of its topological database are out of date. The Link-State Request packet is used to request the pieces of the neighbor’s database that are more up to date. Multiple Link-State Request packets may need to be used. The sending of Link-State Request packets is the last step in bringing up an adjacency.

A router that sends a Link-State Request packet has in mind the precise instance of the database pieces it is requesting, defined by LS sequence number, LS checksum, and LS age, although these fields are not specified in the Link-State Request packet itself. The router may receive even more recent instances in response.

The format of the Link-State Request packet is shown below:

Link-State Request Packet

Version No.

Router ID

Area ID

Checksum

Authentication

Link-State Type

Link-State ID

Advertising Router

Packet Length

Authentication Type

Figure 5-29. Link-State Request Packet

Each advertisement requested is specified by its Link-State Type, Link-State ID, and Advertising Router. This uniquely identifies the advertisement, but not its instance. Link-State Request packets are understood to be requests for the most recent instance.

The Link-State Update Packet

Link-State Update packets are OSPF packet type 4. These packets implement the flooding of link-state advertisements. Each Link-State Update packet carries a collection of link-state advertisements one hop further from its origin. Several link-state advertisements may be included in a single packet.

Link-State Update packets are multicast on those physical networks that support multicast/broadcast. In order to make the flooding procedure reliable, flooded advertisements are acknowledged in LinkState Acknowledgment packets. If retransmission of certain advertisements is necessary, the retransmitted advertisements are always carried by unicast Link-State Update packets.

The format of the Link-State Update packet is shown below:

Link-State Update Packet

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Version No.

Router ID

Area ID

Checksum

Authentication

Number of Advertisements

Link-State Advertisements ...

Packet Length

Authentication Type

Figure 5-30. Link-State Update Packet

The body of the Link-State Update packet consists of a list of link-state advertisements. Each advertisement begins with a common 20-byte header, the link-state advertisement header. Otherwise, the format of each of the five types of link-state advertisements is different.

The Link-State Acknowledgment Packet

Link-State Acknowledgment packets are OSPF packet type 5. To make the folding of link-state advertisements reliable, flooded advertisements are explicitly acknowledged. This acknowledgment is accomplished through the sending and receiving of Link-State Acknowledgment packets. Multiple linkstate advertisements can be acknowledged in a single Link-State Acknowledgment packet.

Depending on the state of the sending interface and the source of the advertisements being acknowledged, a Link-State Acknowledgment packet is sent either to the multicast address AllSPFRouters, to the multicast address AllDRouters, or as a unicast packet.

The format of this packet is similar to that of the Data Description packet. The body of both packets is simply a list of link-state advertisement headers.

The format of the Link-State Acknowledgment packet is shown below:

Link-State Acknowledgment Packet

Version No.

Router ID

Area ID

Checksum

Authentication

Link-State Advertisement Header ...

Packet Length

Authentication Type

Figure 5-31. Link-State Acknowledgement Packet

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Each acknowledged link-state advertisement is described by its link-state advertisement header. It contains all the information required to uniquely identify both the advertisement and the advertisement’s current instance.

Link-State Advertisement Formats

There are five distinct types of link-state advertisements. Each link-state advertisement begins with a standard 20-byte link-state advertisement header. Succeeding sections then diagram the separate linkstate advertisement types.

Each link-state advertisement describes a piece of the OSPF routing domain. Every router originates a router links advertisement. In addition, whenever the router is elected as the Designated Router, it originates a network links advertisement. Other types of link-state advertisements may also be originated. The flooding algorithm is reliable, ensuring that all routers have the same collection of linkstate advertisements. The collection of advertisements is called the link-state (or topological) database.

From the link-state database, each router constructs a shortest path tree with itself as root. This yields a routing table.

There are four types of link state advertisements, each using a common link state header. These are:

• Router Links Advertisements

• Network Links Advertisements

• Summary Link Advertisements

• Autonomous System Link Advertisements

The Link State Advertisement Header

All link state advertisements begin with a common 20-byte header. This header contains enough information to uniquely identify the advertisements (Link State Type, Link State ID, and Advertising Router). Multiple instances of the link state advertisement may exist in the routing domain at the same time. It is then necessary to determine which instance is more recent. This is accomplished by examining the link state age, link state sequence number and link state checksum fields that are also contained in the link state advertisement header.

The format of the Link State Advertisement Header is shown below:

Link-State Advertisement Header

Link-State Age

Link-State ID

Options Link-State Type

Advertising Router

Link-State Sequence Number

Link-State Checksum

Length

Figure 5-32. Link-State Advertisement Header

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Field Description

Link State Age The time is seconds since the link state advertisement was

originated.

Options The optional capabilities supported by the described portion of

the routing domain.

Link State Type The type of the link state advertisement. Each link state type

has a separate advertisement format. The link state type are as follows:

Type Description

1 Router Links

2 Network Links

3 Summary Link (IP Network)

4 Summary Link (ASBR)

5 AS External Link

Link State ID This field identifies the portion of the internet environment that

is being described by the advertisement. The contents of this field depend on the advertisement’s Link State Type.

Advertising Router The Router ID of the router that originated the Link State

Advertisement. For example, in network links advertisements this field is set to the Router ID of the network’s Designated Router.

Link State Sequence Number

Detects old or duplicate link state advertisements. Successive instances of a link state advertisement are given successive Link State Sequence numbers.

Link State Checksum The Fletcher checksum of the complete contents of the link

state advertisement, including the link state advertisement header except for the Link State Age field.

Length The length in bytes of the link state advertisement. This

includes the 20-byte link state advertisement header.

Table 5-16. Link-State Advertisement Header

Router Links Advertisements

Router links advertisements are type 1 link state advertisements. Each router in an area originates a routers links advertisement. The advertisement describes the state and cost of the router’s links to the area. All of the router’s links to the area must be described in a single router links advertisement.

The format of the Router Links Advertisement is shown below:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Routers Links Advertisements

Link-State Age

Link-State ID

Advertising Router

Link-State Sequence Number

Link-State Checksum

Reserved Reserved Number of Links

VBE

Link ID

Link Data

Type No. Of TOS TOS 0 Metric

TOS

...

Link ID

Link Data

Options Link-State Type

Length

Metric

Figure 5-33. Routers Links Advertisement

In router links advertisements, the Link State ID field is set to the router’s OSPF Router ID. The T – bit is set in the advertisement’s Option field if and only if the router is able to calculate a separate set of routes for each IP Type of Service (TOS). Router links advertisements are flooded throughout a single area only.

Field Description

V – bit When set, the router is an endpoint of an active

virtual link that is using the described area as a Transit area (V is for Virtual link endpoint).

E – bit When set, the router is an Autonomous System

(AS) boundary router (E is for External).

B – bit When set, the router is an area border router (B is

for Border).

Number of Links The number of router links described by this

advertisement. This must be the total collection of router links to the area.

Table 5-17. Routers Links Advertisement

The following fields are used to describe each router link. Each router link is typed. The Type field indicates the kind of link being described. It may be a link to a transit network, to another router or to a stub network. The values of all the other fields describing a router link depend on the link’s Type. For example, each link has an associated 32-bit data field. For links to stub networks this field specifies the

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

network’s IP address mask. For other link types the Link Data specifies the router’s associated IP interface address.

Field Description

Type A quick classification of the router link. One of the following:

Type Description

1 Point-to-point connection to another router.

2 Connection to a transit network.

3 Connection to a stub network.

4 Virtual link.

Link ID Identifies the object that this router link connects to. Value

depends on the link’s Type. When connecting to an object that also originates a link state advertisement (i.e. another router or a transit network) the Link ID is equal to the neighboring advertisement’s Link State ID. This provides the key for looking up an advertisement in the link state database.

Type Link ID

1 Neighboring router’s Router ID.

2 IP address of Designated Router.

3 IP network/subnet number.

4 Neighboring router’s Router ID

Link Data Contents again depend on the link’s Type field. For connections

to stub networks, it specifies the network’s IP address mask. For unnumbered point-to-point connection, it specifies the interface’s MIB-II ifIndex value. For other link types it specifies the router’s associated IP interface address. This latter piece of information is needed during the routing table build process, when calculating the IP address of the next hop.

No. of TOS The number of different Type of Service (TOS) metrics given for

this link, not counting the required metric for TOS 0. If no additional TOS metrics are given, this field should be set to 0.

TOS 0 Metric The cost of using this router link for TOS 0.

Table 5-18. Routers Links Advertisements − Continued

For each link, separate metrics may be specified for each Type of Service (TOS). The metric for TOS 0 must always be included, and was discussed above. Metrics for non-zero TOS are described below. Note that the cost for non-zero TOS values that are not specified defaults to the TOS 0 cost. Metrics must be listed in order of increasing TOS encoding. For example, the metric for TOS 16 must always follow the metric for TOS 8 when both are specified.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Field Description

TOS IP Type of Service that this

metric refers to.

Metric The cost of using this

outbound router link, for traffic of the specified TOS.

Table 5-19. Routers Links Advertisement − Continued

Network Links Advertisements

Network links advertisements are Type 2 link state advertisements. A network links advertisement is originated for each transit network in the area. A transit network is a multi-access network that has more than one attached router. The network links advertisement is originated by the network’s Designated router. The advertisement describes all routers attached to the network, including the Designated Router itself. The advertisement’s Link State ID field lists the IP interface address of the Designated Router.

The distance form the network to all attached routers is zero, for all TOS. This is why the TOS and metric fields need not be specified in the network links advertisement.

The format of the Network Links Advertisement is shown below:

Network Link Advertisements

Link-State Age

Link-State Sequence Number

Link-State Checksum

Options

Link-State ID

Advertising Router

Length

Network Mask

Attached Router

Figure 5-34. Network Link Advertisement

Field Description

Network Mask The IP address mask for the network.

Attached Router The Router Ids of each of the routers attached to the

network. Only those routers that are fully adjacent to the Designated Router (DR) are listed. The DR includes itself in this list.

Table 5-20. Network Link Advertisement

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Summary Link Advertisements

Summary link advertisements are Type 3 and 4 link state advertisements. These advertisements are originated by Area Border routers. A separate summary link advertisement is made for each destination known to the router, that belongs to the Autonomous System (AS), yet is outside the area.

Type 3 link state advertisements are used when the destination is an IP network. In this case the advertisement’s Link State ID field is an IP network number. When the destination is an AS boundary router, a Type 4 advertisement is used, and the Link State ID field is the AS boundary router’s OSPF Router ID. Other that the difference in the Link State ID field, the format of Type 3 and 4 link state advertisements is identical.

Summary Link Advertisements

Link-State Age

Link-State ID

Advertising Router

Link-State Sequence Number

Link-State Checksum

Network Mask

TOS Metric

Options

Length

Figure 5-35. Summary Link Advertisement

For stub area, Type 3 summary link advertisements can also be used to describe a default route on a per-area basis. Default summary routes are used in stub area instead of flooding a complete set of external routes. When describing a default summary route, the advertisement’s Link State ID is always set to the Default Destination − 0.0.0.0, and the Network Mask is set to 0.0.0.0.

Separate costs may be advertised for each IP Type of Service. Note that the cost for TOS 0 must be included, and is always listed first. If the T-bit is reset in the advertisement’s Option field, only a route for TOS 0 is described by the advertisement. Otherwise, routes for the other TOS values are also described. If a cost for a certain TOS is not included, its cost defaults to that specified for TOS 0.

Field Description

Network Mask For Type 3 link state

advertisements, this indicates the destination network’s IP address mask. For example, when advertising the location of a class A network the value 0xff000000

TOS The Type of Service that the

following cost is relevant to.

Metric The cost of this route.

Expressed in the same units as the interface costs in the router links advertisements.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Table 5-21. Summary Link Advertisement

Autonomous Systems External Link Advertisements

Autonomous Systems (AS) link advertisements are Type 5 link state advertisements. These advertisements are originated by AS boundary routers. A separate advertisement is made for each destination known to the router that is external to the AS.

AS external link advertisements usually describe a particular external destination. For these advertisements the Link State ID field specifies an IP network number. AS external link advertisements are also used to describe a default route. Default routes are used when no specific route exists to the destination. When describing a default route, the Link Stat ID is always set the Default Destination address (0.0.0.0) and the Network Mask is set to 0.0.0.0.

The format of the AS External Link Advertisement is shown below:

AS External Link Advertisements

Link-State Age

Link-State ID

Advertising Router

Link-State Sequence Number

Link-State Checksum

Network Mask

TOS Metric

Forwarding Address

External Route Tag

Options

Length

Figure 5-36. AS External Link Advertisement

Field Description

Network Mask

e IP address mask for the advertised destination.

E – bit The type of external metric. If the E – bit is set, the metric

specified is a Type 2 external metric. This means the metric is considered larger than any link state path. If the E – bit is zero, the specified metric is a Type 1 external metric. This means that is comparable directly to the link state metric.

Forwarding Address Data traffic for the advertised destination will be forwarded to

this address. If the Forwarding Address is set to 0.0.0.0, data traffic will be forwarded instead to the advertisement’s originator.

TOS The Type of Service that the following cost is relevant to.

Metric The cost of this route. The interpretation of this metric

depends on the external type indication (the E – bit above).

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

External Route Tag A 32-bit field attached to each external route. This is not used

by the OSPF protocol itself.

Table 5-21. AS External System Advertisement

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

CONFIGURING THE SWITCH USING THE

CONSOLE INTERFACE

The DES-3326 supports a console management interface that allows the user to connect to the switch’s management agent via a serial port and a terminal or a computer running a terminal emulation program. The console can also be used over the network using the TCP/IP Telnet protocol. The console program can be used to configure the switch to use an SNMP-based network management software over the network.

This chapter describes how to use the console interface to access the switch, change its settings, and monitor its operation.

Switch configuration settings that are saved to non-volatile RAM using Save Changes from the Main Menu are retained in the switch’s memory, and are reloaded when the switch is rebooted.

Before You Start

The DES-3326 supports a wide array of functions and gives great flexibility and increased network performance by eliminating the routing bottleneck between the WAN and the intranet. Its function in a network can be thought of as a new generation of wire-speed router that performs routing functions in hardware, rather than in software.

General Deployment Strategy

The DES-3326 has many automatic features to detect the network topology and adapt to changes in this topology, but it is recommended that a network scheme be developed and entered statically into the DES-3326.

1. Determine how the network would be best segmented. This is probably done using VLANs in an existing layer 2 switched network.

2. Develop an IP addressing scheme. This involves allocating a block of IP addresses to each network segment. Each network subnet is then assigned a network address and a subnet mask.

3. Determine which network resources must be shared by the subnets. Shared resources may be connected directly to the Layer 3 switch, if need be. Static routes to each of the shared resources should be determined.

4. Determine how each subnet will communicate with the WAN or Internet. Again, static routes should be determined and default gateways identified.

5. Develop a security scheme. Some subnets on the network need more security or should be isolated from the other subnets. IP or MAC filtering can be used. Also, one or more VLANs on the Layer 3 switch can be configured without an IP subnet – in which case, these VLANs will

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

function as a layer 2 VLAN and would require an external router to connect to the rest of the network.

6. Develop a policy scheme. Some subnets will have a greater need for multicasting bandwidth, for example. A policy is a mechanism to alter the normal packet forwarding in a network device, and can be used to intelligently allocate bandwidth to time-critical applications such as the integration of voice, video, and data on the network.

7. Develop a redundancy scheme. Planning redundant links and routes to critical network resources can save valuable time in the case of a link or device failure. The DES-3326’s Spanning Tree function can be used to block the redundant link until it is needed.

VLAN Layout

VLANs on the DES-3326 have more functions than on a traditional layer 2 switch, and must therefore be laid-out and configured with a bit more care. Layer 3 VLANs (VLANs that have an IP interface assigned to them) can be thought of as network links – not just as a collection of associated end users. Further, Layer 3 VLANs are assigned an IP interface address and subnet mask to enable IP routing between them.

IEEE 802.1Q VLANs must be configured on the switch before they can be assigned IP interface addresses or subnet masks. Further, the static VLAN configuration is specified on a per port basis. On the DES-3326, a VLAN can consist of end-nodes – just like a traditional layer 2 switch, but a VLAN can also consist of a subnetwork defined by an IP interface address and a subnet mask.

The IP subnets for the network must be determined first, and the VLANs configured on the switch to accommodate the IP subnets. Finally, the IP subnets can be assigned to the VLANs.

Assigning IP Interface Addresses and Subnet Masks to VLANs

The DES-3326 allows the assignment of IP subnets to individual VLANs. Any VLAN configured on the switch that is not assigned an IP subnet, will behave as a layer 2 VLAN and will not be capable of IP routing – even if the switch is in IP Routing mode.

Developing an IP addressing scheme is a complex subject, but it is sufficient here to mention that the total number of anticipated end nodes – for each Layer 3 VLAN – must be accommodated with a unique IP address. It should be noted that the switch regards a VLAN with an IP interface address and corresponding subnet mask assigned as an IP subnet in IP Routing mode.

Defining Static Routes

Routes between the IP interfaces and a default gateway or other router with a WAN connection should be determined beforehand and entered into the static/default routing table on the DES-3326.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Connecting to the Switch

The console interface is used by connecting the Switch to a VT100-compatible terminal or a computer running an ordinary terminal emulator program (e.g., the HyperTerminal program included with the Windows operating system) using an RS-232C serial cable. Your terminal parameters will need to be set to:

• VT-100/ANSI compatible

• 9,600 baud

• 8 data bits

• No parity

• One stop bit

• No flow control

You can also access the same functions over a Telnet interface. Once you have set an IP address for your Switch, you can use a Telnet program (in VT-100 compatible terminal mode) to access and control the Switch. All of the screens are identical, whether accessed from the console port or from a Telnet interface.

Console Usage Conventions

The console interface makes use of the following conventions:

1. Items in <angle brackets> can be toggled between several choices using the space bar.

2. Items in [square brackets]can be changed by typing in a new value. You can use the backspace

and delete keys to erase characters behind and in front of the cursor.

3. The up and down arrow keys, the left and right arrow keys, the tab key and the backspace key, can be used to move between selected items.

4. Items in UPPERCASE are commands. Moving the selection to a command and pressing Enter will execute that command, e.g. APPLY, etc.

The APPLY command makes the configuration active for the current session only. If the switch is rebooted, the unsaved changes will be lost and the last configuration saved to Non-volatile RAM will be loaded into the switch. Use Save Changes from the main menu to enter the current configuration into the switch’s Non-volatile RAM.

First Time Connecting To The Switch

The Switch supports user-based security that can allow you to prevent unauthorized users from accessing the Switch or changing its settings. This section explains how to log onto the Switch.

The passwords used to access the Switch are case-sensitive; therefore, “S” is not the same as “s.”

When you first connect to the Switch, you will be presented with the first login screen

(shown below).

Press Ctrl+R to refresh the screen. This command can be used at any time to force the console program in the switch to refresh the console screen.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 6-1. Initial Console screen

The factory default Username is “admin”, there is no factory default password. Enter “admin” for the Username and leave the Password field blank to access the console initially

Enter the factory default username (“admin”) and leave the Password field blank. Press Enter and Access will be given to the main menu, as shown below:

Figure 6-2. Main Menu

The first user automatically gets Root privileges (See Table 6-1). It is recommended to create at least one Root-level user for the Switch.

Creating User Accounts

To create a new user account, highlight Setup User Accounts from the Main Menu and press Enter:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 6-3. Main Menu

Figure 6-4. Setup User Accounts Menu

User Accounts Management

From the Main Menu, highlight Setup User Accounts and press Enter, then the Setup User Accounts menu appears.

1. Toggle the Action field to Add using the space bar. This will allow the addition of a new user. The other options are Delete, this allows the deletion of a user entry, and Update, this allows for changes to be made to an existing user entry.

2. Enter the new user name, assign an initial password, and then confirm the new password. Determine whether the new user should have Root, User+, or User privileges. The space bar toggles between the three options.

3. Highlight APPLY and press enter to make the user addition effective.

4. Press Esc. to return to the previous screen or Ctrl+T to go to the root screen.

5. APPLY makes changes to the switch configuration for the current session only. All

permanent changes must be entered into non-volatile ram using the Save Changes command on the Main Menu.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Root, User+ and Normal User Privileges

There are three levels of user privileges: Root and User+, and User.

Switch

Privilege Configuration Management Root User+ User

Configuration Yes Read Only Read Only

Network Monitoring

Community Strings and Trap Stations

Update Firmware and Configuration Files

System Utilities Yes Ping only Ping only

Factory Reset Yes No No

Reboot Switch Yes Yes No

Yes Read Only Read Only

Yes No No

User Accounts Management

Add/Update/Delet e User Accounts

View User Accounts

Yes No No

Table 6-1. Root, User+, and User Privileges

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Saving Changes

Selecting APPLY from a console menu makes the configuration effective for the current session only. The configuration data will be lost if the switch is restarted. To make the configuration effective after a switch restart, select Save Changes to enter the configuration into non-volatile (NV-RAM).

The DES-3326 has two levels of memory: normal RAM and non-volatile or NV-RAM. Configuration changes are made effective by highlighting APPLY and pressing Enter. When this is done, the settings will be immediately applied to the switching software in RAM, and will immediately take effect.

Some settings, though, require you to restart the switch before they will take effect. Restarting the switch erases all settings in RAM and reloads the stored settings from the NV-RAM. Thus, it is necessary to save all setting changes to NV-RAM before rebooting the switch.

Figure 6-5. Main Menu

To retain any configuration changes permanently, highlight Save Changes from the Main Menu. The following screen will appear to verify that your new settings have been saved to NV-RAM:

Figure 6-6. Save Changes Confirmation screen

Once the switch configuration settings have been saved to NV-RAM, they become the default settings for the switch. These settings will be used every time the switch is rebooted.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Loading Factory Defaults

Loading the factory defaults returns the switch’s configuration to the factory default values. This will clear all settings and restore them to their initial values listed in the appendix.

Figure 6-7. Main Menu

Highlight Reboot from the Main Menu and press Enter.

Figure 6-8. System Reboot menu

To execute a factory reset, highlight either Reboot & Load Factory Default Configuration or Reboot & Load Factory Default Configuration Except IP Address and press enter. A confirmation screen will

appear.

Highlight Yes and press Enter to reset the switch’s NV-RAM to the factory default settings. This will erase any User Accounts (and all other configuration settings) you may have entered and return the switch to the state it was in when it was purchased.

Logging Onto The Switch Console

To log in once you have created a registered user, from the Login screen:

1. Type in your Username and press Enter.

2. Type in your Password and press Enter.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

3. The Main Menu screen will be displayed based on your access level or privilege.

Updating or Deleting User Accounts

To update or delete a user password:

Choose Setup User Accounts from the Main Menu. The following Setup User Accounts menu appears:

Figure 6-9. Setup User Accounts screen

1. Toggle the Action field using the space bar to choose Add, Update, or Delete.

2. Type in the Username for the user account you wish to change and enter the Old Password

for that user account.

3. You can now modify the password or the privilege level for this user account.

4. If the password is to be changed, type in the New Password you have chosen, and press Enter. Type in the same new password in the following field to verify that you have not

mistyped it.

5. If the privilege level is to be changed, toggle the Access Level field until the appropriate level is displayed – Root, User+ or User.

6. Highlight APPLY and press Enter to make the change effective.

7. You must enter the configuration changes into the non-volatile ram (NV-RAM) using Save Changes from the Main Menu if you want the configuration to be used after a switch

reboot.

Only a user with Root privileges can make changes to user accounts.

Viewing Current User Accounts

Access to the console, whether using the console port or via Telnet, is controlled using a user name and password. Up to eight user accounts can be created. The console interface will not let you delete the current logged-in user, to prevent accidentally deleting all of the users with Root privilege.

Only users with the Root privilege can delete users.

To view the current user accounts:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Highlight Setup User Accounts from the Main Menu. The current user accounts can be read from following screen:

Figure 6-10. Setup User Accounts screen

Deleting a User Account

To delete a user account:

Figure 6-11. Setup User Accounts screen

1. Toggle the Action field to Delete.

2. Enter the Username and Old Password for the account you want to delete. You must enter

the password for the account to be able to delete it.

3. Highlight APPLY and press Enter to make the deletion of the selected user take effect.

4. You must enter the configuration changes into the non-volatile ram (NV-RAM) using Save Changes from the Main Menu if you want the configuration to be used after a switch

reboot.

Only users with Root privileges can delete user accounts.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Setting Up The Switch

Basic Setup

This section will help prepare the Switch user by describing the Switch Information, IP Setup, Remote Management Setup, Configure Ports, Serial Port Settings and Switch Settings menus.

Figure 6-12. Main Menu – Switch Information

Switch Information

Highlight Switch Information from the Main Menu and press Enter:

Figure 6-13. Switch Information screen

The Switch Information shows the operation mode of switch (Layer 3 or Layer 2), which (if any) external modules are installed, and the switch’s MAC Address (assigned by the factory and unchangeable). In addition, the Boot PROM and Firmware Version numbers are shown. This information is helpful to keep track of PROM and Firmware updates and to obtain the switch’s MAC address for entry into another network device’s address table – if necessary.

You can also enter the name of the System, its location, and the name and telephone number of the System Administrator. It is recommended that the person responsible for the maintenance of the network system that this Layer 3 switch is installed on be listed here.

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Remote Management Setup

Configuring the Switch’s IP Address

The BOOTP and DHCP Server options for assigning the switch an IP address and subnet mask are only available when the switch is in Layer 2 Only mode. The IP Routing mode requires a manual entry of the IP address and subnet mask.

The Switch needs to have an IP address assigned to it so that an In-Band network management system (for example, the DView or Telnet) client can find it on the network. The IP Setup screen allows you to change the settings for the Ethernet interface used for in-band communication.

The fields listed under the Current Switch IP Settings heading are those that are currently being used by the switch. Those fields listed under the Restart Settings heading are those which will be used after the APPLY button is selected.

To set the switch’s IP address:

Highlight Remote Management Setup from the Main Menu and press Enter.

Figure 6-14. Remote Management Setup menu

The switch’s factory default IP address is 10.90.90.90 with a subnet mask of 255.0.0.0 and a default gateway of 0.0.0.0.

To manually assign the switch’s IP address, subnet mask, and default gateway

address:

Highlight the IP Address field and enter the appropriate IP address.

Highlight the Subnet Mask field and enter the appropriate subnet mask.

If you want to access the switch from a different subnet from the one it is installed on, highlight the Default Gateway field and enter the IP address of the gateway. If you will manage the switch from the subnet on which it is installed, you can leave the default address in this field.

To use the BOOTP/DHCP protocols to assign the switch an IP address, subnet mask, and default gateway address:

Toggle the Get IP From field using the space bar to choose from Manual, BOOTP, or DHCP. This selects how the switch will be assigned an IP address on the next reboot (or startup).

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

The Get IP From options are:

• BOOTP – The switch will send out a BOOTP broadcast request when it is powered up. The BOOTP protocol allows IP addresses, network masks, and default gateways to be assigned by a central BOOTP server. If this option is set, the Switch will first look for a BOOTP server to provide it with this information before using the default or previously entered settings.

• DHCP – The switch will send out a DHCP broadcast request when it is powered up. The DHCP protocol allows IP addresses, network masks, and default gateways to be assigned by a DHCP server. If this option is set, the switch will first look for a DHCP server to provide it with this information before using the default or previously entered settings.

• Manual – Allows the entry of an IP address, Subnet Mask, and a Default Gateway for the switch. These fields should be of the form xxx.xxx.xxx.xxx, where each xxx is a number (represented in decimal form) between 0 and 255. This address should be a unique address on the network assigned for use by the Network Administrator. The fields which require entries under this option are as follows:

• Subnet Mask – A Bitmask that determines the extent of the subnet that the Switch is on. Should be of the form xxx.xxx.xxx.xxx, where each xxx is a number (represented in decimal) between 0 and 255. The value should be 255.0.0.0 for a Class A network, 255.255.0.0 for a Class B network, and 255.255.255.0 for a Class C network, but custom subnet masks are allowed.

• Default Gateway – IP address that determines where packets with a destination address outside the current subnet should be sent. This is usually the address of a router or a host acting as an IP gateway. If your network is not part of an intranet, or you do not want the Switch to be accessible outside your local network, you can leave this field unchanged.

• Management VID – This field allows the entry of a VLAN ID (VID) from which a management station (a computer) will be allowed to manage the switch using TCP/IP (in-band, or over the network). Management stations that are on VLANs other than the one entered in the Management VID field will not be able to manage the switch in-band unless their IP addresses are entered in the Management Station IP Addresses field. Any VID that has been configured on the switch can be entered in this field.

SNMP Settings

Some settings must be entered to allow the switch to be managed from an SNMP-based Network Management System such as SNMP v1 or to be able to access the Switch using the Telnet protocol or the Web-based Manager. Please see the next chapter for Web-based network management information.

To setup the switch for remote management:

Highlight Remote Management Setup from the Main Menu. The following screen appears:

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

Figure 6-15. Remote Management Setup menu

Management stations are computers on the network that will be used to manage the switch. You can limit the number of possible management stations by entering up to three IP addresses in the Management Station IP Settings field. If the three IP Address fields contain all zeros (“0”), then any station with any IP address can access the switch to manage and configure it. If there is one or more IP addresses entered in the IP Address field, then only stations with the IP addresses entered will be allowed to access the switch to manage or configure it.

Setting Up Trap Receivers

This allows the switch to send traps (messages about errors, etc.) to management stations on the network. Highlight Setup Trap Receivers and press Enter. The trap recipients can be setup from the following screen:

Figure 6-16. Setup Trap Recipients menu

The IP Address field is the IP address of a management station (a computer) that is configured to receive the SNMP traps from the switch.

The SNMP Community String is similar to a password in that stations that do not know the correct string cannot receive or request SNMP information from the switch.

The Status field can be toggled between Enabled and Disabled to enable or disable the receipt of SNMP traps by the listed management stations.

100

D-Link DES-3326 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

INTRODUCTION

Layer 3 Switching

The Functions of a Layer 3 Switch

Features

Ports

Performance Features

Layer 2 Features

Layer 3 Switch Features

Traffic Classification and Prioritization

Management

Optional Redundant Power Supply

Fast Ethernet Technology

Gigabit Ethernet Technology

UNPACKING AND SETUP

Unpacking

Installation

Desktop or Shelf Installation

Rack Installation

Power on

Power Failure

IDENTIFYING EXTERNAL COMPONENTS

Front Panel

Rear Panel

Side Panels

Optional Plug-in Modules

1000BASE-T Module

1000BASE-SX Fiber Module

1000BASE-LX Fiber Module

GBIC Two-Port Module

LED Indicators

CONNECTING THE SWITCH

Switch to End Node

Switch to Hub or Switch

10BASE-T Device

100BASE-TX Device

Local Console Management

Diagnostic (console) port (RS-232 DCE)

IP Addresses and SNMP Community Names

Traps

SNMP

Authentication

Traps

MIBs

Packet Forwarding

MAC Address Aging Time

Filtering

Spanning Tree

Bridge Protocol Data Units

Creating a Stable STP Topology

STP Port States

User-Changeable STA Parameters

Illustration of STP

Link Aggregation

VLANs

Notes About VLANs on the DES-3326

IEEE 802.1Q VLANs

802.1Q VLAN Packet Forwarding

802.1Q VLAN Tags

Port VLAN ID

Tagging and Untagging

Ingress Filtering

VLANs in Layer 2 Only Mode

Layer 3-Based VLANs

IP Addressing and Subnetting

Definitions

IP Addresses

Address Classes

Subnet Masking

Calculating the Number of Subnets and Nodes

Classless InterDomain Routing – CIDR

Setting up IP Interfaces

Layer 3-Based VLANs

Internet Protocols

Protocol Layering

Layer 1

Layer 2