D-link DGS-3224TG User Manual
DGS-3224TG
Managed 24-Port Gigabit Ethernet Switch
User’s Guide
First Edition (October 2004)
651TG3224015
Printed In Taiwan
RECYCLABLE
Wichtige Sicherheitshinweise
1. Bitte lesen Sie sich diese Hinweise sorgfältig durch.
2. Heben Sie diese Anleitung für den spätern Gebrauch auf.
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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.
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f – Wenn das Gerät deutliche Anzeichen eines Defektes aufweist.
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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
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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.
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Copyright D-Link Corporation 2002. Contents subject to change without prior notice. D-Link is a registered
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Hardware:
D-Link warrants its hardware products to be free from defects in workmanship and materials, under normal use and service, for
the following periods measured from date of purchase from D-Link or its Authorized Reseller:
Product Type
Complete products One year
Spare parts and spare kits 90 days
Warranty Period
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.
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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.
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Material Authorization (RMA) number. 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.
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Software:
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list of D-Link offices is provided at the back of this manual.
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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
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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
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contact the D-Link office nearest you. An addresses/telephone/fax list of D-Link offices is provided in the back of this manual.
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.
This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not
cause harmful interference, and (2) this device must accept any interference received, including interference that may cause
undesired operation.
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.
Warnung!
Dies ist ein Produkt der Klasse A. Im Wohnbereich kann dieses Produkt Funkstoerungen verursachen.
In diesem Fall kann vom Benutzer verlangt werden, angemessene Massnahmen zu ergreifen.
Precaución!
Este es un producto de Clase A. En un entorno doméstico, puede causar interferencias de radio, en
cuyo case, puede requerirse al usuario para que adopte las medidas adecuadas.
Attention!
Ceci est un produit de classe A. Dans un environnement domestique, ce produit pourrait causer des
interférences radio, auquel cas l`utilisateur devrait prendre les mesures adéquates.
Attenzione!
Il presente prodotto appartiene alla classe A. Se utilizzato in ambiente domestico il prodotto può
causare interferenze radio, nel cui caso è possibile che l`utente debba assumere provvedimenti
adeguati.
BSMI Warning
Table of Contents
About This Guide .................................................................................................................................. 1
Overview of this User’s Guide ............................................................................................................. 1
Introduction .......................................................................................................................................... 2
Features ............................................................................................................................................. 2
Ports ................................................................................................................................................ 2
Performance Features......................................................................................................................... 2
Management .................................................................................................................................... 3
Unpacking and Setup............................................................................................................................ 4
Unpacking .......................................................................................................................................... 4
Installation ......................................................................................................................................... 4
Desktop or Shelf Installation ............................................................................................................ 4
Rack Installation.............................................................................................................................. 5
Power on............................................................................................................................................. 6
Power Failure ................................................................................................................................... 6
Identifying External Components .......................................................................................................... 7
Front Panel......................................................................................................................................... 7
Rear Panel .......................................................................................................................................... 7
Side Panels ......................................................................................................................................... 8
LED Indicators ................................................................................................................................... 8
Connecting The Switch.......................................................................................................................... 9
Switch to End Node ............................................................................................................................ 9
Switch to Hub or Switch ..................................................................................................................... 9
Switch Management and Operating Concepts ..................................................................................... 11
Local Console Management .............................................................................................................. 11
Diagnostic (console) port (RS-232 DCE)..........................................................................................11
IP Addresses and SNMP Community Names ..................................................................................... 12
Traps................................................................................................................................................ 13
MIBs................................................................................................................................................. 14
SNMP ............................................................................................................................................... 14
Authentication ............................................................................................................................... 15
Packet Forwarding ............................................................................................................................ 15
MAC Address Aging Time ............................................................................................................... 15
Filtering............................................................................................................................................ 15
Spanning Tree Protocol ..................................................................................................................... 16
STP Operation Levels ..................................................................................................................... 16
Bridge Protocol Data Units ............................................................................................................. 17
Creating a Stable STP Topology ...................................................................................................... 18
STP Port States .............................................................................................................................. 18
User-Changeable STP Parameters ..................................................................................................20
Illustration of STP .......................................................................................................................... 20
VLANs .............................................................................................................................................. 22
Notes About VLANs on the DGS-3224TG........................................................................................ 22
IEEE 802.1Q VLANs....................................................................................................................... 22
802.1Q VLAN Packet Forwarding ...................................................................................................23
802.1Q VLAN Tags ......................................................................................................................... 24
Port VLAN ID.................................................................................................................................. 25
Tagging and Untagging................................................................................................................... 26
Ingress Filtering ............................................................................................................................. 26
DHCP ............................................................................................................................................... 27
Configuring the Switch Using the Console Interface ............................................................................ 29
Before You Start ............................................................................................................................... 29
Connecting to the Switch .................................................................................................................. 29
User Accounts Management ............................................................................................................. 32
Save Changes ................................................................................................................................... 34
Factory Reset ................................................................................................................................. 35
Configuration ................................................................................................................................... 38
Configure IP Address...................................................................................................................... 39
Configure Switch Information and Advanced Settings .................................................................... 41
Configure Ports .............................................................................................................................. 43
Configure Spanning Tree Protocol .................................................................................................. 44
Configure Static (Destination-Address Forwarding) Table ............................................................... 46
Configure VLANs ............................................................................................................................ 49
Configure IGMP Snooping .............................................................................................................. 53
Configure Trunk............................................................................................................................. 55
Configure Port Mirroring ................................................................................................................ 56
Configure Class of Service, Default Priority, and Traffic Class ........................................................ 57
Configure RS232 and SLIP ............................................................................................................. 60
Network Monitoring .......................................................................................................................... 61
Port Utilization ............................................................................................................................... 62
Port Error Packets.......................................................................................................................... 63
Port Packet Analysis....................................................................................................................... 63
Browse MAC Address ..................................................................................................................... 64
Switch History................................................................................................................................ 65
IGMP Snooping .............................................................................................................................. 66
Browse Multicast Status ................................................................................................................ 67
VLAN Status .................................................................................................................................. 68
SNMP Manager Configuration........................................................................................................... 68
System Utilities ................................................................................................................................ 69
Upgrade Firmware from TFTP Server .............................................................................................. 70
Use Configuration File on TFTP Server ...........................................................................................71
Save Settings to TFTP Server .......................................................................................................... 72
Save History Log to TFTP Server..................................................................................................... 73
Ping Test ........................................................................................................................................ 74
Reboot .............................................................................................................................................. 75
Web-Based Network Management ....................................................................................................... 78
Introduction ..................................................................................................................................... 78
Getting Started ................................................................................................................................. 78
Configuration ................................................................................................................................... 82
IP Address...................................................................................................................................... 82
Switch Information......................................................................................................................... 83
Advanced Settings.......................................................................................................................... 84
Port Configuration.......................................................................................................................... 85
Port Mirroring ................................................................................................................................ 86
Port Trunking................................................................................................................................. 87
IGMP Snooping .............................................................................................................................. 87
Spanning Tree................................................................................................................................ 88
Static Forwarding Table ................................................................................................................. 91
VLANs............................................................................................................................................ 92
Port Default Priority ....................................................................................................................... 95
Class of Traffic ............................................................................................................................... 96
Class of Service .............................................................................................................................. 96
RS232 & SLIP ................................................................................................................................ 98
Management..................................................................................................................................... 99
Security IP ..................................................................................................................................... 99
SNMP Manager .............................................................................................................................. 99
Trap Manager............................................................................................................................... 100
User Accounts.............................................................................................................................. 100
Monitoring...................................................................................................................................... 101
Port Utilization ............................................................................................................................. 101
Packets ........................................................................................................................................ 102
Errors .......................................................................................................................................... 108
Size .............................................................................................................................................. 113
MAC Address Table ...................................................................................................................... 115
IGMP Snooping Table ................................................................................................................... 116
VLAN Multicast Table................................................................................................................... 117
IGMP Multicast Table ................................................................................................................... 117
VLAN Status ................................................................................................................................ 117
Maintenance................................................................................................................................... 118
TFTP Services............................................................................................................................... 118
Switch History.............................................................................................................................. 120
Ping Test ...................................................................................................................................... 121
Save Changes............................................................................................................................... 122
Factory Reset ............................................................................................................................... 123
Restart System............................................................................................................................. 123
Connection Timeout ..................................................................................................................... 124
Logout.......................................................................................................................................... 124
Help................................................................................................................................................ 124
Technical Specifications .................................................................................................................... 125
Cable Lengths ................................................................................................................................... 128
Runtime Switching Software Default Settings.................................................................................... 129
Understanding and Troubleshooting the Spanning Tree Protocol....................................................... 130
Blocking State.............................................................................................................................. 130
Listening State ............................................................................................................................. 131
Learning State.............................................................................................................................. 132
Forwarding State.......................................................................................................................... 133
Disabled State.............................................................................................................................. 134
Troubleshooting STP....................................................................................................................... 135
Spanning Tree Protocol Failure .................................................................................................... 135
Full/Half Duplex Mismatch.......................................................................................................... 136
Unidirectional Link ...................................................................................................................... 137
Packet Corruption ........................................................................................................................ 138
Resource Errors ........................................................................................................................... 138
Identifying a Data Loop ................................................................................................................ 138
Avoiding Trouble .......................................................................................................................... 138
Brief Review of Bitwise Logical Operations......................................................................................... 141
Index................................................................................................................................................. 142
DGS-3224TG Gigabit Ethernet Switch User’s Guide
ABOUT THIS GUIDE
This User’s guide tells you how to install your DGS-3224TG, how to connect it to your Gigabit Ethernet
network, and how to set its configuration using the built-in console interface.
Overview of this User’s Guide
• Chapter 1, “Introduction.” Describes the Switch and its features.
• Chapter 2, “Unpacking and Setup.” Helps you get started with the basic installation of the Switch.
• Chapter 3, “Identifying External Components.” Describes the front panel, rear panel, and LED
indicators of the Switch.
• Chapter 4, “Connecting the Switch.” Tells how you can connect the DGS-3224TG to your Gigabit
Ethernet network.
• Chapter 5, “Switch Management and Operating Concepts.” Talks about Local Console
Management via the RS-232 DCE console port and other aspects about how to manage the
Switch.
• Chapter 6, “Using the Console Interface.” Tells how to use the built-in console interface to change,
set, and monitor Switch performance and security.
• Chapter 7, “Web-Based Network Management.” Tells how to manage the Switch through an
Internet browser.
• Appendix A, “Technical Specifications.” Lists the technical specifications of the DGS-3224TG.
• Appendix B, “Cable Lengths.” Contains chart for fiber-optic and copper cable maximum
distances.
• Appendix C, “Factory Default Settings.”
• Appendix D, “Understanding and Troubleshooting the Spanning Tree Protocol.”
• Appendix E, “Brief Review of Bitwise Logical Operations.”
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
1
INTRODUCTION
This section describes the features of the DGS-3224TG.
Features
The DGS-3224TG was designed for departmental and enterprise connections. As an all-gigabit-port
switch, it is ideal for backbone and server connection. Powerful and versatile, the switch eliminates
network bottlenecks while giving users the capability to fine-tune performance
Switch features include:
Ports
• Twenty high performance 1000BASE-T ports for making 10/100/1000 connections to a
backbone, end stations, and servers.
• Four GBIC ports to connect fiber optic media to another switch, server or network backbone.
• 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
• Store-and-forward switching scheme.
• High-speed data forwarding rate of 1,488,100 pps per port at 100% of wire-speed for 1000 Mbps
speed.
• Optimized 32K entry address database without flooding.
• 802.1D Spanning Tree support. Can be disabled on the entire switch or on a per-port basis.
• 802.1Q Tagged VLAN support, including GVRP (GARP VLAN Registration Protocol).
• Support for 200 VLANs in total, including 64 static VLANs.
• IGMP snooping support per switch.
• Link aggregation support for up to 6 trunk groups and 16 trunk members per group.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
Management
• RS-232 console port for out-of-band network management via a console terminal.
• Spanning Tree Algorithm Protocol for creation of alternative backup paths and prevention of
network loops.
• SNMP V.1.
• 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)
802.1P/Q MIB (RFC 2674)
Interface MIB (RFC 2233)
Mini-RMON MIB (RFC 1757) – 4 groups. The RMON specification defines the counters for
the receive functions only. However, the DGS-3224TG provides counters for both receive
and transmit functions.
• Supports Web-based management.
• TFTP support.
• BOOTP support.
• DHCP Client support.
• Password enabled.
• Telnet remote control console.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
2
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 DGS-3224TG 24-Port Gigabit Ethernet Switch
• Mounting kit: 2 mounting brackets and screws
• Four rubber feet with adhesive backing
• One AC power cord
• This User’s Guide
If any item is found missing or damaged, please contact your local reseller for replacement.
Installation
Use the following guidelines when choosing a place to install the switch:
• The surface must support at least 6.5 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.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
Figure 2-1. Installing rubber feet for desktop installation
Rack Installation
The DGS-3224TG 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
Then, use the screws provided with the equipment rack to mount the witch on the rack.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
Figure 2-2B. Installing in an equipment rack
Power on
The switch can be used with AC power supply 100-240 VAC, 50 - 60 Hz. The switch’s power supply will
adjust to the local power source automatically and may be powered on without having any or all LAN
segment cables connected.
After the switch is plugged in, 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 selftest. After approximately 20 seconds, the LED will light again to indicate the switch is in a ready
state.
Power Failure
As a precaution in the event of a power failure, unplug the switch. When power is resumed, plug the
switch back in.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
3
IDENTIFYING EXTERNAL COMPONENTS
This chapter describes the front panel, rear panel, side panels, and LED indicators of the DGS-3224TG.
Front Panel
The front panel of the switch consists of LED indicators, an RS-232 communication port, 20
1000BASE-T ports, and 4 GBIC ports.
Figure 3-1. Front panel view
• 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.
• Comprehensive LED indicators display the status of the switch and the network (see the LED
Indicators section below).
• Four GBIC ports to connect fiber optic media to another switch, server, or network backbone.
• Twenty 1000BASE-T Ethernet ports for 10/100/1000 connections to a backbone, end stations,
and servers.
Rear Panel
The rear panel of the switch contains an AC power connector.
Figure 3-2. Rear panel view
• 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.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
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 3-3. 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.
LED Indicators
The LED indicators of the switch include Status, Speed, Full Duplex, and Link/Activity. The following
shows the LED indicators for the switch along with an explanation of each indicator.
Figure 3-4. LED indicators
• Status – This indicator on the front panel blinks green when the system is booting up. It is solid
green when the system is operating normally and solid red if the system fails.
• Speed – There are three rows of indicators for the 20 copper ports. The top LED is solid green for
1000 Mbps connections and solid amber for 100 Mbps connections. The indicator is off for 10
Mbps connections.
• Full Duplex – This indicator for the 20 copper ports is located in the middle row. Solid green
indicates a full-duplex connection. The LED is off for half-duplex connections.
• Act/Link – This indicator is located in the bottom row for the 20 copper ports and directly to the
left of the four GBIC ports. In each case, these indicators light solid green when there is a secure
connection (or link) to a device on any of the ports. The LEDs blink green whenever there is
reception or transmission (i.e. Activity--Act) of data occurring on a port.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
4
CONNECTING THE SWITCH
This chapter describes how to connect the DGS-3224TG to your Gigabit 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.
An end node can be connected to the switch via a two-pair Category 3, 4, 5, or 5e UTP/STP cable—for
optimal performance, Category 5e is recommended. The end node should be connected to any of the
ports of the switch.
Figure 4-1. Switch connected to an End Node
The Link/Act LEDs on the bottom row of the front panel of the device light green when the link is
valid. The LED on the top row indicates port speed. It will light solid green for 1000 Mbps
connections, solid amber for 100 Mbps connections, and will remain off for 10 Mbps connections. A
blinking green LED on the bottom row indicates packet activity on that port.
Switch to Hub or Switch
These connections can be accomplished in a number of ways using a normal cable.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
• A 10BASE-T hub or switch can be connected to the switch via a two-pair Category 3, 4, 5, or 5e
UTP/STP cable.
• A 100BASE-TX hub or switch can be connected to the switch via a two-pair Category 5 or 5e
UTP/STP cable.
• A 1000BASE-T switch can be connected to the switch via four-pair straight Category 5 or 5e
UTP/STP cable.
Figure 4-2. Switch connected to a normal (non-Uplink) port on a hub or switch using a straight or crossover
cable
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
5
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 DGS-3224TG 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.
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
• Flow Control None
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
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 Procedure screen
The switch’s MAC address can also be found from the console program under the Switch Information
menu item, as shown below.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
Figure 5-2. Switch Information menu
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 allow you 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
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
from a factory reset in that configuration settings saved to non-volatile RAM used to
reconfigure the switch.
• 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.
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.
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 HP OpenView or DView.
SNMP performs the following functions:
• Sending and receiving SNMP packets through the IP protocol.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
• Collecting information about the status and current configuration of network devices.
• Modifying the configuration of network devices.
The DGS-3224TG 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.
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
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 and destination 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 17.2 to 2,200 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 MAC Address filtering.
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
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 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 that 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.
Spanning Tree Protocol
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.
This automatic network reconfiguration provides maximum uptime to network users. However, the
concepts of the Spanning Tree Algorithm and protocol are a complicated and complex subject and must
be fully researched and understood. It is possible to cause serious degradation of the performance of
the network if the Spanning Tree is incorrectly configured. Please read the following before making any
changes from the default values.
The switch STP performs the following functions:
• Creates a single spanning tree from any combination of switching or bridging elements.
• Automatically reconfigures the spanning tree to compensate for the failure, addition, or removal
of any element in the tree.
• Reconfigures the spanning tree without operator intervention.
STP Operation Levels
STP calculates the Bridge Identifier for each switch and then sets the Root Bridge and the Designated
Bridges.
The following are the user-configurable STP parameters for the switch level:
Parameter Description Default
Value
Bridge Identifier A combination of the User-set
priority and the switch’s MAC
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
(Not userconfigurable except
by setting priority
below)
Priority A relative priority for each switch –
Hello Time The length of time between
Maximum Age Timer Measures the age of a received
Forward Delay Timer The amount time spent by a port
address. The Bridge Identifier
consists of two parts: a 16-bit
priority and a 48-bit Ethernet MAC
address
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
BPDU for a port and ensures that
the BPDU is discarded when its
age exceeds the value of the
maximum age timer.
in the learning and listening states
waiting for a BPDU that may
return the port to the blocking
state.
Table 5-1. STP Parameters – Switch Level
32768
2 seconds
20 seconds
15 seconds
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.
32768
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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
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
• 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, but 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
• 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
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
• 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
• From forwarding to disabled
• From disabled to blocking
Figure 5-3. STP Port State Transitions
When you enable STP, 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
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DGS-3224TG Gigabit Ethernet Switch User’s Guide
Port cost 19
Bridge Priority 32,768
Table 5-3. Default STP Parameters
User-Changeable STP 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 in Figure 5-3.
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 5-4. 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.
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