EXP Computer PathBuilder S200 User Manual

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PathBuilder™ S200 Series Switch

Bridging

Notice

Restricted Rights Notification for U.S. Government Users

The software (including firmware) addressed in this manu al is provided to the U.S.

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If the software is procured for use by the Department of Defense, the following legend applies:

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Use, duplication, or disclosure by the Government

is subject to restrictions as set forth in

subparagraph (c)(1)(ii) of the

Rights in Technical Data and Computer Software

clause at DFARS 252.227 -70 13 .

If the software is procured for use by any U.S. Government entity other than the Department of Defense, the following notice applies:

Notice

Notwithstanding any other lease or license agreement that may pertain to, or accompany the delivery of, this computer software, the rights of the Government regarding its use, repr odu cti o n, and disclos ure are as set forth in F A R 52.227 -19 (C ).

Unpublished - rights reserved under the copyright laws of the United States.

Notice (continued)

Proprietary Material

Information and software in this document are proprietary to 3C om (or its Suppliers) and without the express prior permission of an officer of 3Com, may not be copied, reproduced, disclosed to others, publi shed, or used, in whol e or in part , for any purpos e other t han that for which it is being made available. Use of software described in this document is subject to the terms and conditions of the 3Com Software License Agreement.

This document is for information purposes only and is subject to change without notice.

Part No. T0008-16, Rev. F First Printing October 1998

Manual is current for Release 5.2M.

Bridging

Overview

Functionality PathBuilder S200 serie s swit ches su pport b ridgi ng of dat a traf f ic for Ethern et LANs.

Bridging LAN traffic minimizes your networking costs by eliminating the need for redundant networks and maximizes the availability of dedicated facilities such as servers and printers, as well as public Frame Relay and X.25 services, across multiple LANs.

Remote Bridging Solutions

PathBuilder S200 series switches are intended for use in remote bridging solutions. This means the PathBuilder S200 series sw itch is best used t o connect a re mote LAN to the WAN to connect to other remot e LANs in you r networ k, as sh own in Fig ure 1.

Ethernet

PB S200

Token

Ring

PB S200

X.25/FR

PB S200

Token

Ring

Ethernet

Figure 1. PathBuilder S200 Series Switch Bridge Combining Traffic from Serial Devices

Figure 1 shows PathBuilder S200 series switches acting as remote bridges to combine data traffic from Ethernet LANs to the WAN to connect to other remote LANs in the network.

Bridging 1

Mixed LAN Support PathBuilder S200 series switches support mixed LAN bridging, meaning you can

configure an Ethernet interface in the same node. Refer to the “Mixed LAN

Bridging” section on page 8 for more details.

Translational Bridging

PathBuilder S200 series switches can use the Translational Bridging feature to bridge traffic between Ethernet Networks. Translational Bridging provides a PathBuilder S200 series switch with the capability to bridge non-routable protocols. For information about enabling and configuring Translational Bridging, refer to the “Configuring Translational Bridging” section on page 37.

No Local Bridging As mentioned earlier, PathBuilder S200 series switches are not intended for use in

local bridging applications where one LAN is connected directly to another LAN. It is not recommended you use PathBuilder S200 series switches to perform local bridging.

Transparent Bridging

Transparent Bridging (TB) is the method used by PathBuilder S200 series switches to bridge Ethernet LAN traffic from one Ethernet LAN to another one across a WAN.

Refer to Transparent Bridging for Ethernet LANs on page 48 for more details on these bridging operations.

Supported T raffic The PathBuilder S200 series switch family supports many types of protocols for

bridging operations. Some of the supported protocols include:

•Async

•SDLC

• Bisync

• Transparent Polled Async

• HDLC

• X.25

• Frame Relay

• Burroughs Poll Select

• NCR Bisync

2 Bridging

In This Manual Topic See Page

Bridging Features and Capabilities .............................................................. 5

Token Ring LAN ...................................................................................... 6

Ethernet LAN ........................................................................................... 8

Mixed LAN Bridging ............................................................................... 10

MAC Addressing ..................................................................................... 11

LLC2 Local Termination ................................................................. ......... 12

Autolearn for Local Termination .............................................................. 13

Filtering .................................................................................................... 14

Spanning Tree Protocol ............................................................................ 15

Dual Ethernet LANs ................................................................................. 16

Basic Remote Bridging Examples ................................................................ 17

Bridge Hardware Components in PathBuilder S200 Series Switches .......... 19

Setting Up WAN Operation for Bridging ..................................................... 20

Configuring the PathBuilder S200 Series Switch for Bridging Operation ... 22

Bridge Parameters .................................................................................... 23

Bridge Link Parameters ............................................................................ 27

LAN Connection Table ............................................................................ 32

Limiting Bridge Frame Sizes ................................................................... 36

Configuring Translational Bridging ......................................................... 38

Source Route Bridging for Token Ring LANs ............................................. 40

Bridge Frame Handling ............................................................................ 41

Source Route Bridging Operation ............................................................ 42

Configuring Source Route Bridging Operation ....................................... 45

Connecting a Station to a Server in Source Route Bridging .................... 47

Transparent Bridging for Ethernet LANs ..................................................... 53

Forwarder Database and Spanning Tree .................................................. 58

Using Filters ............................................................................................. 59

Transparent Bridge Configuration Parameters ......................................... 61

Bridge Filtering ............................................................................................ 62

MAC Address Filtering ............................................................................ 63

MAC Address Filtering Examples ........................................................... 67

Identifying Address Links for MAC Addressing ..................................... 72

MAC Wildcard Filtering .......................................................................... 73

Configuring the MAC Address Filter Table ............................................. 74

Protocol Filtering ..................................................................................... 78

Configuring the Protocol Filter Table ...................................................... 79

NetBIOS Name Filtering .......................................................................... 84

Configuring NetBIOS Name Filtering ..................................................... 86

NetBIOS Name Filtering Statistics .......................................................... 92

NetBIOS Packet Formats . ........................................................................ 93

Spanning Tree Protocol Entity (STPE) ......................................................... 94

STPE Parameter Setting Considerations ......................................... ......... 97

Spanning Tree Timers .............................................................................. 103

Bridge Forward Delay Timer ................................................................... 105

LLC2 Local Termination .............................................................................. 108

Configuring Local Termination ................................................................ 114

Deleting LT Configuration Records ......................................................... 121

Mixed LAN Operation ................................................................................. 122

Dual LAN Ethernet ....................................................................................... 125

LAN Server Subsystem ................................................................................ 128

Configuring the LSS Record .................................................................... 130

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In This Notice

(continued)

Topic See Page

Bridge Statistics ............................................................................................ 132

Spanning Tree St atistics ........................................................................... 133

Detailed Bridge Link Statistics ................................................................ 135

Bridge Link Filter Summary .................................................................... 138

Transparent Bridge Forwarding Table Statistics ...................................... 140

Transparent Bridge Detailed Bridge Link St atistics ................................. 142

LAN Connection Statistics ....................................................................... 144

LLC2 LT Session Summary Statistics ...................................................... 149

LLC2 LT Detailed Session Statistics ........................................................ 151

Reset Statistics .......................................................................................... 155

4 Bridging

Bridging Features and Capabilities

Introduction This section describes bridging features and capabilities of PathBuilder S200 series

switches.

Bridging Primer As mentioned earlier, Bridging extends the size and coverage of a Local Area

Network (LAN). PathBuilder S200 series switches provide bridging support for up to two 802.3 (Ethernet) LAN interfaces per node or one 802.5 (Token Ring) LAN interface) per node, and up to 32 remote bridge connections.

A PathBuilder S200 series switch b ridge can be connected t o a WAN backbone made up of X.25, Frame Relay, or both, as shown in Figure 2.

Token

Ring

PB S200

FR/X.25

PB S200

Figure 2. Example of Typical PathBuilder S200 Series Switch Bridging Application

PathBuilder S200 series switches are best suited for remote bridging operations where traffic flows from one LAN through a WAN bridged by at least two PathBuilder S200 series switches to another LAN.

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Bridging Features and Capabilities

Ethernet LAN

What Is It? Ethernet is a common implementation of LAN topology wherein stations are

connected using a bus topology. Stations access the Ethernet using Carrier Sense with Multiple Access and Collision Dete ction (CSMA/CD ).

PathBuilder S200 Series Switch Support for Ethernet

Example of Basic Ethernet Frame Format

PathBuilder S200 seri es switch Ethernet f unct io nal it y c omplies with the IEEE 802.3 specifications and provides Transparent Bridging to transport many different protocols over the Wide Area Network (WAN) to remote destinations. Supported protocols include:

• Novell Netware

•DECnet

• Banyan Vines

Figure 3 shows the basic frame formats for Ethernet frames supported by PathBuilder S200 series switches.

Ethernet Frame Format

Preamble

8Octets

Destination Source Type

662445-1500

64-1518

Data

FCS

Figure 3. Frame Format for Ethernet Frames

802.3 MAC Frame

Figure 4 shows the supported 802.3 Ethernet MAC Frame format.

Format

802.3 MAC Frame Format

Preamble

SFD Destination Source Len Data Unit Pad FCS

DSAP SSAP Control Higher Layer Information

1 1 1 or 2

802.3.LLC

42-1497

Octets

Figure 4. 802.3 Ethernet MAC Frame Format Example

6 Bridging

Bridging Features and Capabilities

Example of Ethernet Bridge Operation

Figure 5 shows an example of two Ethernet LANs connected across a WAN using two PathBuilder S200 serie s switc hes as br idges . The ex ample sho ws a Frame Rel ay WAN application, but you can also bridge across an X.25 WAN.

Frame Relay

PB S200PB S200

Figure 5. Ethernet Bridge Example

For More Details... For more details on bridging Ethernet LAN traffic, see Transparent Bridging for

Ethernet LANs on page 48.

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Bridging Features and Capabilities

Mixed LAN Bridging

What is It? PathBuilder S24x, 26x, and 27x switches support a mixture of Token Ring and

Ethernet interfaces configured in the same node. This means the PathBuilder S24x, 26x, and 27x switch is able to perform remote Transparent bridging for Ethernet LANs from the same PathBuilder S24 x, 26x, and 27x swit ch as shown in Fi gure 6. If you happen to configure two Ether net LAN inter fa ces in the same node, instead of a mix of one Ethernet and one Token Ring, you can perform local Transparent bridging between the two Ethernet LANs.

Ethernet 1

Ethernet 2

Port 13

Port 19

PB S200

WAN

PB S200

Ethernet 1

Ethernet 2

Figure 6. Example of Mixed LAN Bridging in PathBuilder S24x, 26x, and 27x Switch

Note

Mixed LAN operation does not support translational bridging, meaning you cannot pass LAN traffic from an Ethernet LAN to a Token Ring LAN without using some sort of conversion software.

For More Details Refer to the “Mixed LAN Operation” section on page 114 for more details.

8 Bridging

Bridging Features and Capabilities

MAC Addressing

What Is It? Bridges, whether they using Transparent Bridging, operate at the Data Link Layer,

which is concerned with MAC addressing. The MAC Address is a 6-byte MAC (Media Access Control) address that identifies stations on a LAN. The IEEE administers distribution of the MAC address to ensure no duplicates occur in MAC addressing. This is accomplished by assigning a unique MAC address to each manufacturer. Each manufacturer then assigns sequential values to the lower three bytes for each interface manufactured.

For More Details For more details on MAC Address filtering, see the section “MAC Address

Filtering” section on page 58”in this manual.

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Bridging Features and Capabilities

LLC2 Local Termination

PathBuilder S200 series switch support includes LLC2 Local Termination for your Bridging operations when pas sing SNA/SDLC data tra f fic. LLC2 Local Termination lets specific Token Ring ports generate and respond to LLC2 polls with local acknowledgments, thereby preserving bandwidth and preventing session timeouts.

Local Termination, also referred to as “spoofing,” provides an efficient means for carrying out an LLC2 session between two SNA end stations attached to separate Token Ring LANs connected by a Wide Area Network (WAN).

Additionally, Local Termination provides detailed statistics on LLC2 sessions.

LT Example Figure 7 shows a network where running LLC2 Local Termination at the edge point

PathBuilder S200 series switches enables spoofing from one side of the network to the other across multiple Token Rings.

SNA

FEP

LLC2

Keepalives/Acks

LLC2

LLC2 Keepalives/Acks

LLC2

Keepalives/Acks

Figure 7. Local Termination Example

For More Details... See“LLC2 Local Termination” section on page 100 in this guide.

10 Bridging

Bridging Features and Capabilities

Autolearn for Local T ermination

What Is It? Local Termination Autolearn reduces the amount of configura tion you need to do by

letting you spoof remote sessions without configuring a MAC address and a Service Access Point (SAP) for each station running a session to the host Front End Processor (FEP).

Since Local Termination supports up to 256 sessions for the PathBuilder S24x, 26x, and 27x switch, Local Termination Autolearn can save you consid erabl e time duri ng the configuration process.

Local Termination Autolearn is a default feature with PathBuilder S200 series switches operating software meaning it requires no special configuration, other than configuring the remote host MAC address in the PathBuilder S200 series switch Local Termination (LT) Station tables.

It does not interfere with previously configured Local Termination spoofing sessions.

Example Figure 8 shows how a PathBuilder S200 series switch automatically learns the

address of PCs connected to the local bridge so you can pass data traffic to the host without configuring entries in the Local Termination Station table for each PC session.

The PC’s destination MAC address must match the MAC address configured in the remote Host FEP for local PB S200 to automatically learn LAN MAC addresses.

Configure the Host FEP MAC address and SAP in the

LT station tables of the local an d remote bridges. PB S200 automatically learns MAC addresses of any LAN devices with matching desti na ti on MAC addresses.

The local PB S200 running Local

Termination Autolear n automatically learns MAC addresses of stations on

Destination MAC addresses set up 40:00:00:00:10:88

local LAN.

Figure 8. Example of Local Termination Autolearn

PB S200

Host MAC address: 40:00:00;00:10:88

FEP

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Bridging Features and Capabilities

Filtering

What Is It? Filtering lets you restrict data traffic from certain segments of your network. There

are different methods used to filter data traffic on a bridged network. PathBuilder S200 series switch support for filtering includes:

• MAC Address Filtering

• NetBIOS Name Filtering

• Protocol Filtering

Mac Address Filtering

NetBIOS Name Filtering

MAC Addressing is important in a bridging operation because one of the most common tasks in a bridging environment is to provide filtering of data frames. Filtering provides a way of stopping certain d evi ce s f rom c ommunicating with other devices in a network. One way to filter traffic through a bridge is by identifying the devices you want to block by their MAC Addresses.

For more details on MAC Address filtering, see the section “MAC Address Filtering” section on page 58” in this manual.

The NetBIO S Name Filtering feature of PathBuilder S200 serie s switches le ts you restrict or filter all NetBIOS broadcasts, except those to or from a list of servers.

NetBIOS Name Filtering compares NetBIOS broadcasts to a “pattern” that may have a wild card “*” character at the end. For example, if all servers have a naming convention with the fir st pa rt of t he name the same, for example, “SVR...”, then you can complete only one ent ry i n t he Ne tBIOS Filter Table to permit broadcasts to and from the “SVR*” name pattern.

With NetBIOS Name Filters, you can block the local service name (for example, “SNA_GW”) on the WAN link so that NetBIOS broadcasts to and from that name are not forwarded across to the internetwork.This feature lets the branches use the same name for their loc al SNA ser vi ce a nd you can configure all th e workstations to access the same local SNA name.

Refer to “NetBIOS Name Filtering” section on page 76 in this guide.

Protocol Filtering Protocol filtering prevents nodes operating with a certain protocol from operating

outside their intended scope. Refer to the“Protocol Filtering” section on pag e 70 for more details.

12 Bridging

Bridging Features and Capabilities

Spanning T ree Protocol

What Is It? Spanning Tree Protocol reduces multiple bridge paths between LANs to a single

path. Instead of a mesh network with several paths to a destination, the Spanning Tree Protocol remaps the network so that only one path is active for traffic between any source station and any destination station. The other paths block any frames between the LANs.

A spanning tree network eliminates parallel paths and traffic loops. The PathBuilder S200 series switch implementation of the Spanning Tree Protocol

Entity (SPTE) conforms to IEEE 802.ID specifications. Refer to the IEEE 802.ID specification for more detailed information on Spanning Tree Protocol operation.

Automatic & Manual Spanning Tree Support

PathBuilder S200 series switch support both automatic and manual spanning tree operations.

If you do not want to configure spanning tree operation yourself, you can use the automatic spanning tree creation option. Remember that a all bridges in your network must be configured to automatic spanning tree operation to allow for the spanning tree protocol to determine the spanning tree.

For More Details... See the“Spanning Tree Protocol Entity (STPE)” section on page 86.

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Bridging Features and Capabilities

Dual Ethernet LANs

What Is It? The PathBuilder S24x, 26x, and 27x switch supp orts up to two Ethernet LANs in t he

same node. This means you can connect up to two Ethernet LANs to a single PathBuilder S24x, 26x, and 27x switch to perform bridging and routing of LAN traffic across the WAN to multiple Ethernet LANs. Before Dual Ethernet LAN, the PathBuilder S24x, 26x, and 27x switch supported only one Ethernet LAN port for remote bridging and routing of LAN traffic.

For More Details... See the “Dual LAN Ethernet” section on page 117.

14 Bridging

Basic Remote Bridging Examples

Introduction This section shows some common examples of bridging applications using

PathBuilder S200 series switches.

Remote Bridging Across a WAN

Extended Bridging for Multiple LANs

Figure 9 shows a common Source Route Bridging operation for PathBuilder S200 series switches where two Token Ring LANs are attached across a WAN. For example, two LANs could be bridged using two PathBuilder S200 series switches interconnected by an X.25 or Frame Relay link. Bridged traffic flows between the bridges over a Swit ched Virtual Circuit (SVC) tha t conne cts them t ogether a cross th e WAN (or Permanent Virtual Circuit (PVC) for Frame Relay).

Token

Ring 1

PBS200 Node 1

X.25/Frame Relay

PBS200

Node 2

Token

Ring 2

Figure 9. PB S200s Connecting LANs via an X.25/Frame Relay Link

If more than two remote LANs are involved in your bridging application, the bridge arrangement can be e xtended s o that individua l LAN pair s are co nnected by di ff erent bridges, as shown in Figure 10.

Token

Ring 1

Node 1

Bridge 1 Bridge 2

Node 2

Bridge 1 Bridge 3

Token

Ring 2

Token

Ring 3

Node 3

Bridge 2 Bridge 3

SVC Connectors (PVC for Frame Relay)

Figure 10. Two-Port Bridges Connecti ng Mult ipl e Token Ring LANs

In this example, each pair of LANs is connect ed by a sing le bridge fo rmed by bridge pairs.

• Bridge 1 interconnects Token Ring 1 and Token Ring 2

• Bridge 2 interconnects Token Ring 1 and Token Ring 3

• Bridge 3 interconnects Token Ring 2 and Token Ring 3

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Basic Remote Bridging Examples

A Less Complex Extended Bridge

Figure 11 shows a possible arrangement of SVCs (PVCs for Frame Relay) that produces the same bridge arrangement as shown in Figure 10.

Token

Ring 1

Token

Ring 3

Node 1

Bridge 1 Bridge 2

SVC Connectors

Node 3

Bridge 2 Bridge 3

Node 2

Bridge 1 Bridge 3

Token

Ring 2

Figure 11. Example of Bridges in an SVC Arrangement

In this arrangement, all LAN segments are one hop away from each other since they are directly attached by a single pair of bridges. In Figure 11, Token Ring 1 is one bridge away from Token Ring 2 and Tok en Ring 3 and the same applies for the othe r rings.

From a bridged netw or k po int of view, Token Ri ng 1 i s one bridge away fr om Token Ring 3, but Node 1 is not directly connected to Node 3. Traffic between Token Ring 1 and T oke n Ring 3 does n ot have to pass th rough Token Ring 2. This is an important advantage in configuring bridge networks with the PathBuilder S200 series switch because you can form a minimal bridge network to accomplish the desired interconnectivity.

16 Bridging

Bridge Hardware Components in PathBuilder S200 Series Switches

Introduction This section describes bridge hardware configuration and connections for the

PathBuilder S200 series switch.

Bridge Configuration and Connections

Figure 12 shows the physical connections of the modules that provide bridging functiona lity for PathBuilder S200 series switch . This figure shows a LAN port module and supporting WAN Adapter module within a PathBuilder S200 series switch. The LAN port module is br oken out int o a driver and a forwarder to show the concept of bridge links.

At each end node, the bridge has connectio ns referr ed to as brid ge links. Bridge links that connect to the LAN are referred to as LAN bridge links. Bridge links that connect to remote bridges across the WAN are referred to as WAN bridge links.

LAN Link Numbers range from 1 to 4: up to two LAN connections are supported for Ethernet.

LAN Port Module

Token

Ring

LAN

Driver

Forwarder

LAN

Bridge

. . . .

Up to 32 WAN links can be defined (numbered 5 to 36), o ne f or each bridge connection over an SVC (PVC for Frame Relay).

WAN

Adaptor

X.25 SVCs connected to SVCs on network ports (PVCs for Frame Relay)

Figure 12. LAN Port Module and WAN Adapter Module (Logical View)

The LAN port consists of low level drivers and the bridge forwarder. This can be viewed as the functioning bridge. The WAN Adapter is closely associated with the bridge. The WAN Adapter provides the network services that the bridge requires in order to function over the WAN network. The principal service is establishing and maintaining S VC (PVC for Frame Relay) connections to remote LAN bridge forwarders so that virtual circuits can be formed betwee n the forwarders.

The bridge sees the LAN and th e WAN (by means o f the WAN Adapter) as networ ks it is attached to by links. There are a total of 36 links: four LAN links and 32 WAN links.

LAN Interface Support

The PathBuilder S200 series switch supports only one LAN per node, so only one link is needed for the LAN port connection: link number 1. The PathBuilder S24x, 26x, and 27x switch supports up to two Ethernet LANs per node. See “Dual LAN

Ethernet” section on page 117 for more details on this functionality. On the PathBuilder S200 series switch links numbered 2 to 4 are not used and are

reserved for future configurations. WAN links are numbered 5 to 36 and provide up to 32 WAN connection links which correspond to potential bridges.

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Bridge Hardware Components in PathBuilder S200 Series Switches

18 Bridging

Setting Up WAN Operation for Bridging

Setting Up W AN Operation for Bridging

Introduction With the 3Com Bridging Protocol option, you can use PathBuilder S200 series

switches to connect remot e LANs a cr oss a Wide Area Network (WAN), as shown in Figure 13.

Codex Proprietary Protoc ol ID LAN Connection Subaddress

Critical Parameter s for WAN Operation

LAN

AAA

LAN

DDD

Node 1

Bridge 1

Half

Bridge 2

Half

Node 3

Bridge 2

Half

Bridge 3

Half

WAN

SVC Connectors

Node 2

Bridge 1 Bridge 3

Half Half

LAN CCC

Figure 13. Interface Connections Between WAN and LAN

Before you can use a PathBuilder S200 series switch as a bridge to connect LANs over a WAN, you must configure the following two parameters in the Node record for the bridge node. In most cases, use default values:

• Codex Proprietary Protocol ID

• LAN Connection Subaddress

You also need to configure the LAN Connection Table. Entries in this table are for the WAN Adapter and specify co nnections going acr oss a wid e area ne twork, such as X.25, Frame Relay, or other proprietary protocols.

Codex Proprietary Protocol ID

The Protocol Identi fi er (ID) is placed o n t he Call User Data fie ld of t he Call Request packet. This packet is generated by the Autocall used to establish a circuit for a bridge link. If the bridge link is not configured to initiate an autocall, then this configured value is ma tched with that found in an In coming Call pa cket to det ermine if the call should be established.

To define the Codex Proprietary Protocol ID, select a value within the designated range. Normally you would not configure a value different from the default value. The only reason to use a different value is if the default value conflicts with one already in use.

It is recommended that the Protocol ID value in all network nodes be the same.

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LAN Connection Subaddress

The LAN Connection Subaddresses identifies all LAN Connections. Incoming calls with a network address consisting of the Node Address specified in the Node record and the LAN Connection Subaddress, specified in the LAN Connection Table, are verified and allowed to connect to the WAN Adapter in order to reach the LAN bridges.

The LAN Connection Subaddress is appended to the calling address of the Call Request packet if generated and sent by the WAN Adapter. Use the default value unless it conflicts with an address already in use.

Refer to the “LAN Connection Table” section on page 31 for more details.

20 Bridging

Configuring the PathBuilder S200 Series Switch for Bridging Operation

Introduction This section shows you how to configure a PathBuilder S200 series switch for

bridging operation.

What You Need to Configure

When you are performing a Transparent Bridging operation, configure the following records in the bridge node:

•Node Record

• LAN Port Record

•Bridge Record

• Bridge Link Record

• LAN Connection Table

• Optional Filter Tables

• LAN Server Subsystem (LSS) Record (optional)

• Autocall Mnemonic Table (Some of the WAN Adapter connections are configured to Autocall.)

• Routing Table (At the destination node, a LAN Connection [LCON] entry is needed for the WAN Adapter.)

For general details on configuring the Node record and the LAN Port record, refer to the PathBuilder S200 Series Basics Protocols. For details on LAN Server Subsystem configuration, see the “LAN Server Subsystem” section on page 120.

The following sections describe how to configure the records and tables critical for performing bridging on a PathBuilder S200 series switch.

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Bridge Parameters

Bridge Port Record Parameters

After you configure the Node record and the LAN Port record for the bridge node, configure the Bridge parameters. Figure 14 shows the parameters that make up the Bridge Parameters record.

Node: Address: Date: Time: Menu: Configure Bridge Path:

Bridge Parameters

*Max Number of Bridge Links *STPE Control Bad Hello Threshold Bad Hello Timeout Learn Only Period Aging Period Bridge WAN Data Priority Bridged Protocols Local Bridge ID

Figure 14. Configure Bridge Parameters

Parameters These parameters make up the Bridge Parameter Record.

*Maximum Number of Bridge Links

Range: 36 to 250 Default: 36 Description: Specifies the maximum number of bridge links allowed. Boot Type: A change to this parameter requires a Node boot to take effect.

22 Bridging

Configuring the PathBuilder S200 Series Switch for Bridging Operation

*STPE Control

Range: AUTO, MAN Default: MAN Description: The Spanning Tree Protocol Entity (STPE) module in the Path-

Builder S200 series switch provides automatic calculation of the spanning tree. Spanning tr ee all ows f or the prop er support of single route broadcast frames that occur in LANs. This parameter controls how a bridge determines the Spanning Tree: either automatically using the STPE, or manually using additional parameters in the bridge link record.

• AUTO: The bridge participates in Spanning Tree Protocol (STP) and automatically determines the single path between LANs using the “Path Costs” assigned to the different links. Bridge protocol data units (BPDUs) are special frames used to continually communicate this information between bridges.

• MAN: The Spanning Tree is configured by the network administrator. This is done using the STPE Link State parameter found in the next section, “Bridge Link Parameters.”

Configure all bridges in your network to MANual if you are not an expert user of Spanning Tree protocol operation. This prevents problems in operation, especially when lower speed WAN links are involved in forming bridges.

Note

If STPE Control parameter is set to MAN, the following parameter appears.

Bad Hello Threshold

Range: 10 to 30 Default: 15 Description: Use this parameter to generate alarms when some bridges are

configured AUTO and others are configured MAN in order to detect nonmatching configurations.

A Bad Hello counter is incremented when a HELLO Protocol Data Unit (PDU) is received while the STPE Control parameter is configured to MAN. An event (alarm) is generated when the counter exceeds the value of this parameter. The event is generated only once during the Bad Hello Time.

Note

If STPE Control parameter is set to MAN, the following parameter appears.

Bad Hello Timeout

Range: 10 to 30 Default: 15

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Bad Hello Timeout

(continued)

Description: Represents the timeout value in minu tes. Th e Bad Hel lo coun te r is

reset when the timeout expires and can be used to control how frequently the Hello counter reaches its alarm threshold.

Learn Only Period (used for Ethernet only)

Range: 2 to 604800 Default: 10 Description: The time in seconds that a bridge is prevented from forwarding

frames after the forwarding is cleared due to a node boot.

Aging Period (used for Ethernet only)

Range: 2 to 1000000 Default: 10 Description: Specify the time in seconds that a learned entry in the Forwarding

Table is allowed to remain in the table without being updated (relearned). If t he e ntry is not updat ed within this time period, it is discarded from the table.

Bridge WAN Data Pri o rity (used for Ethernet only)

Range: EXP, HIGH, MED, LOW Default: HIGH Description: Specify the transmission priority of the bridged data over the

WAN.

24 Bridging

Configuring the PathBuilder S200 Series Switch for Bridging Operation

Note

If STPE Control parameter value is AUTO, this parameter appears.

Bridged Protocols

Range: None, IP, IPX Default: None Description: Specify the routable protocols that can be bridged across BROUT

or BRID links. “None” specifies no routable protocols (IP, IPX) will be bridged. “IP” specifies that IP packets can be bridged. “IPX” specifies that IPX packets can be bridged.

Note

Any combination of the available selections may be specified by summing, such as IP + IPX.

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Bridge Link Parameters

Introduction The bridge uses Bridge Li nks as connections to the LAN and WAN networks.

The LAN Bridge Link connects the bridge directly to the local LAN, and its parameters control the characteristics of this connection.

The WAN Bridge Link parameters let you establish and maintain SVC connections to a remote LAN bridge. The bridge views the LAN bridge links and the WAN bridge links as links to the network s attached to it.

Bridge Link Parameters

Figure 15 shows the Bridge Lin k parameters.

Node: Address: Date: Time: Menu: Configure Bridge Path:

Bridge Parameters Bridge Link Parameters

Entry Number Bridge Type Bridge ID Hop Count Limit Largest Frame Size MAC Address Filter Action Protocol Filter Action NETBIOS Name Filter Action STPE Link State Link Mode Virtual Ring Number

Figure 15. Configure Bridge Link Menu

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Parameters These parameters make up the Bridge Link Record.

Entry Number

Range: 1, 5 to 36 Default: 1 Description: Specify the Bridge Link number that references this record. Two

Ethernet LANs can be configured on the PathBuilder S24x, 26x, and 27x switch using 1 and 2. Links 1-4 are reserved for LAN port connections.

There are 32 possible WAN Bridge Links, numbered 5 to 36. Bri dges are formed by PVC/SVC connec tions to WAN bridge li nks in r emote PathBuilder S200 series switch. Each bridge link used in a WAN connection is connected to a remote bridge link and such an arrangement forms a bridge between the two LANs.

At the destination node, th e routing t able must have an entry tha t lists the destination por t as LCON (LAN Connect ion). This al lows the cal l to be directed to a connection on the WAN Adapter.

Note

The following parameter appears if you enter 5 top 36 at the Entry Number parameter.

Bridge_Type

Range: SR, TB, BOTH_SR_AND_TB Default: TB Description: This is the bridge type for links connect ing to WANs. It defines the

kind of bridging that will be employed on the link. It applies only to WAN links, number 5 to 36, the maximum number of links allowed.

Choose:

• TB - to perform Transparent Bridging

• BOTH_SR_AND_TB - when you perform mixed LAN bridging operation. This lets the node perform TB and SRB operations simultaneo usl y.

Bridge ID

Range: 0 to 15 Default: 1 Description: A bridge number uniquely id ent if ie s a b ri dge when mor e t han one

bridge is used to span the same two segments. This should match the Bridge ID of the remote Bridge half.

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Hop Count Limit

Range: 0 to 7 Default: 7 Description: Specifies the maximum number of bridges through which a

broadcast frame may pass on the way to its destination.

Largest Frame Size

Range: 516, 1500, 2052, 4472 Default: 2052 Description: Specifies the maximum size of the INFO field that this Bridge

Link can send and receive. The minimum value of this parameter or of adjacent Bridge Li nk or values of Largest Frame Size of bridge wide parameter is used to determine whether a modification of the Routing Control field of RIF is necessary.

MAC Address Filter Action

Range: NONE, PASS, BLOCK Default: NONE Description: Specify how the MAC Address Filter Table is used.

• NONE: No MAC address filtering using the MAC Address Filter Table is performed for this link.

• PASS: Look in the MA C Address Filter Table for an entry with a matching MAC frame address and take the filtering action specified by this filter table. If no matching entry is found, this value indicates that this frame should be passed.

• BLOCK: Look in the MAC Address Filter Table for an entry with a matching MAC frame address and take the filtering action specified by this filter table. If no matching entry is found, this value indicates that this frame should be blocked.

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Protocol Filter Action

Range: NONE, PASS, BLOCK Default: NONE Description: Functions similarly to the MAC Address Filtering Action

parameter. The filtering is applied to each lin k. Fr ames pass in g on a link can be either incoming or outgoing.

• NONE: No Protocol fi ltering using t he Proto col Filter Table is to be performed for this link.

• PASS: Look in the Protocol Filter Table for an entry with a matching frame address and take the filter in g action specified by this filter table. If no ma tching entry is found, this value indicates that this frame should be passed.

• BLOCK: Look in the Protocol Fil te r Table for an entry with a matching frame address and take the filter in g action specified by this filter table. If no matching entry is found, this value indicates that this frame should be blocked.

NETBIOS Name Filter Action

Range: PASS, BLOCK, NONE Default: NONE Description: Specify how NetBIOS Name Filter is used on this node:

• PASS: Pass all frames with NETBIOS name not listed in NETBIOS Name Filter Table.

• BLOCK: Block all frames with NETBIOS name not listed in NETBIOS Name Filter Table.

• NONE: No NETBIOS name filtering to be perf ormed for t his link.

STPE Link State

Range: FORWARD, BLOCK Default: FORWARD Description: Specify whether to forward or block data frames when the STPE

Control parameter is configured to MAN.

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Link Mode

Range: NORMAL,RFC1294, TRANS Default: NORMAL Description: Specify one of the following:

• NORMAL - Bridge link connects to another Bridge using the Link Control Protocol to determine remote Ring Number. This option is not supported for PVC connections. Use another option for PVC connections.

• RFC1294- Bridge link uses RFC1294 (or RFC1490) bridging to connect to another Bridge or Frame Relay Access Device. A Bridge Link Virtual Ring Number is required

• TRANS - Translational Bridging support for PathBuilder S24x, 26x, and 27x switch only.

Boot Type: A change to this parameter requires a node boot to take effect.

Note

The following parameter appears if you set Link Mode to RFC1294

Virtual Ring Number

Range: 0001-0FFF hexadecimal Default: 0000 Description: This is a virtual ring number that is used by the Bridge Link for

connecting to another Bridge or Frame Relay Access Device via RFC1294 or RFC1490 Bridging. It must match the virtual ring number of the connecting Bridge or Frame Relay Access Device.

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LAN Connection Table

Introduction The LAN Connection Table provides information about the connections that cross

over the WAN.

LAN Connection Table Parameters

Figure 16 shows the LAN Connection Table parameters.

Node: Address: Date: Time: Menu: Configure Path:

Node Port

: : :

LAN Connection Table

Entry Number *LAN Forwarder Type LAN Connection Type Router Interface Number Encapsulation Type Autocall Mnemonic LCON Queue Limit Billing Records Traffic Priority

Figure 16. LAN Connection Table Menu

Parameters These parameters make up the LAN Connection Table Record.

Entry Number

Range: 1 to 32 Default: 1 Description: Specify the entry number used to reference this table record.

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*LAN Forwarder Type

Range: ROUT, BRID, BROUT Default: ROUT Description: Specify if the LAN Connection is to pass bridged, routed, and/or

brouted traffic:

• BRID: Bridged LAN traffic is transported across this connection.

• ROUT: Routed LAN traffic is transported across this connection.

• BROUT: Both bridge d and route d LAN tr af fic are trans porte d across this connection.

Boot Type: Changes to this parameter require a Node Boot to take effect.

LAN Connection Type

Range: PT_to_PT, GROUP Default: PT_to_PT (Point-to-Point) Description: Specify whether this LAN Connection defines a point-to-point

connection across the WAN, or is part of a group of LAN Connections. If configur ed as GROUP, multiple LAN Connections can use the same Router Interface number. If configured as PT_to_PT, the Router Interface configured must be unique to this LAN Connection.

Note

This parameter appears if the LAN Forwarder Type is configured as ROUT or BROUT.

Boot Type: When changing from GROUP to PT_PT, a Node boot is required.

Otherwise, a Table and Node Record boot is required.

Router Interface Number

Range: 5 to n, where n = 36 to 254 Default: 5 Description: Specifies a Router Interface using this LAN Connection record.

This connection makes it possible to pass LAN data through the WAN network to a remote router. The allowable range of values reflect the maximum number of IP or IPX interfaces set in the IP or IPX Parameters Menu.

Note

This parameter appears if the LAN Forwarder Type is configured as ROUT or BROUT.

Boot Type: Changes to this parameter require a Node Boot to take effect.

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Encapsulation Type

Range: RFC 877, RFC 1294 Default: CODEX Description: Specify the type of encapsulation used over this LAN connection.

Encapsulation types supported include:

• CODEX: Codex Proprietary Encapsulation

• RFC 877/1356: RFC 877/1356 X.25 protocol encapsulation for IP

• RFC 1294/1490: RFC 1 294/1490 mul tiprotocol encapsul ation over Frame Relay

Boot Type: Changes to this parameter require a Table and Node Record boot

to take effect.

Autocall Mnemonic

Range: 0 to 8 alphanumeric characters Default: 0 (blank) Description: Specify the mnemonic name used when the LAN connection is

configured to autocalli ng. A cor re spon ding entry must be made in the Mnemonic Table. A blank entry means autocalling will not be initiated by this LAN connect ion entry. The LAN connector at the remote device must initiate the call. If configured, the Autocall Mnemonic references a remote address which will be called by the LAN connection.

Specifically, it must equal the node address of the node to which the remote LAN is attached (the LAN to which we want to bridge). The LAN connection subaddress configured in the node record is appended to this address to form the complete ca lled address of an X.25 call.

LCON Queue Limit

Range: 0 to 65536 Default: 16000 Description: The LCON Queue Limit parameter specifies the maximum

number of bytes that are queued for this LAN before transmission on the WAN link. Set this par ameter fo r two sec onds of da ta on th e WAN link.

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Billing Records

Range: OFF, ON Default: OFF Description: Enables or disables the creation (storing and printing) of billing

records for the LAN connection:

• ON: Billing records are generated.

• OFF: Billing records are not generated.

Traffic Priority

Range: LOW, MED, HIGH, EXP Default: HIGH Description: Specify the Tr affic Priority level of this LAN Connection.

• LOW: One Low Priority packet is sent for every Traffic Priority Ste p number of Medium priority p ackets.

• MED: One Medium priority packet is sent for every Traffic Priority Ste p number of Hig h priority pack ets.

• HIGH: High is the first level of priority packets sent, if no expedite priority packets are sent.

• EXP: Expedite priority packets have the highest priority and use all of the link bandwidth that they need. Any remaining bandwidth is shared by the high, medium, and low priority packets.

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Configuring the PathBuilder S200 Series Switch for Bridging Operation

Limiting Bridge Frame Sizes

Overview Although there are valid reasons for using larger frame sizes on bridges, there are

limiting factors that must be considered when selecting a maximum frame size. There are several reasons for limiting the maximum size of the frame, especially

where bridging is done remotely across a WAN:

• The larger the frame, the longer it takes to transmit the frame on a WAN link.

• Increasing the frame size also causes a reduction in frame overhead.

Conversely, the smaller the frame, the less time it takes to t ransmit the fr ame. Since a smaller frame cannot be for war ded by an inte rmed iary node until it is fu lly rec eived, a large fra me cannot be f orward ed fo r the time i t take s to t ransmit an d recei ve it over a given link. On a LAN, this time is less of an issue where the link speed is approximately 10 Mbps. On a WAN link, it becomes an issue because the transmission times for large frames become significant.

Example of Frame Sizes

Figure 17 shows the effect on trans it de lay acr oss a n etwork f or two c ases: in one, a n end system sends a large packet as a single frame and in the other, the same large packet is sent as three smaller packets.

Large Packet

Total Transit

Tim e

Small Packet

Total Transit

Time

End

System

End

System

Node 1 Node 2 Node 3

End

System

End

System

Figure 17. How Packet Size Affects Transit Delay

Small packets are forwar ded more quickl y by interme diate nodes resulting in the end system receiving several short frames in less time than a long frame. How much improvement is achieved depends on the transmission times and line speeds involved. The trade-off in this case is that even though the transit delay is reduced, the packet-per-second load is increased on all three nodes (and two end systems) involved. In this case, the factor is at least three if continuous streams of packets are involved.

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Increasing the fra me size als o caus es the re ducti on in frame ove rh ead. If a 1000 byte data packet required a 50 byte header (frame + IP + TCP), then if 2000 bytes were placed in the frame with th e same frame, the di f fere nce in over hea d is 50/100 0 = 5% versus 2.5%. As the size of the data increases, the overhead becomes even less. However, a t th ese levels, the gain is marginal. Other factors ma y re duce thi s met hod of gain considerably. For example, intermediate systems have a limit on how large a frame they can handle.

As the size of the fr ame become s larger, there is a correspo nding i ncr ease i n the ti me the frame spends in transmission media. The error rate of transmission media is finite and becomes a pro blem when the ti me for tra nsmittin g a frame becomes l ong enough that the probability of an e rror occurring during the transmission time is likely. An error on a large frame with its subsequent retransmission means the media are used with unproductive transmissions and reduced efficiency.

Standard Frame Sizes

In general, these industry standards can be used as a guideline for selecting the maximum frame size.

Max Frame Size Line Speed Range (kbps)

512 9.6 to 38.4 1500 38.4 to 56 2052 56 to 1544 4472 1544

Bridge T ransi t T ime The transit time for bridged traffic within a PathBuilder S200 series switch is fixed to

an upper bound of approximately one second. If the time is exceeded, the frame is discarded. This avoids extra traffic being sent (especially due to LLC2 recovery procedures).

Duplicate frames will f rustr at e normal r ecover y proced ure s and caus e extr a tr af fic to be generated. When a frame is discarded in this manner, the port statistic in the

Detailed Port Stat screen displays “Frames Discarded: Congestion.”

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Configuring Translational Bridging

Introduction This section explains how to configure your PathBuilder S24x, 26x, and 27x switch

to implement the Translational Bridging feature.

What is Translational Bridging

Translational Bridging allows a PathBuilder S24x, 26x, and 27x switch to bridge traffic between Ethernet and Token Ring networks. Upon receiving traffic from one network the PathBuilder S24x, 26x, and 27x switch’s Source Route translates the

data into a translational bridge format that can be used by the other network. For Translational Bridging to function, several conditions must exist:

• The Token Ring network must conform to IEEE standard 802.5 and the Ethernet network mst conform to 802.3.

• The PathBuilder S24x, 26x, and 27x switch must contain a 4 Meg FLASH and be using one of these software options: Option 71 to 75.

Note

In a single node, Translational Bridging performance is limited to 350 packets per second.

Parameter To enable Translational Bridging, you need to set the parameter Link Mode =

TRANS (in the Bridge Link Para meters Re cord) . Als o, be sur e the pa rameter Virtual Ring Number is set to a unique value.

Configuration Guidelines

These factors should be considered when configuring your PathBuilder S24x, 26x, and 27x switch for Translational Bridging:

• Only one link in a Pa thBuil der S24x , 26x, and 27x swit ch can hav e the p arameter Link Mode = TRANS.

• Only Bridge Link with Bridge Type = SR can have Link Mode = TRANS.

• LLC Termination is not supported between Token Ring and Ethernet when using Translational Bridging.

• You can increase the value of the parameter Aging Period (in the Bridge Parameters Record) to limit the relearning of the entries in the Translational Bridging MAC Address.

For more information a bout confi guring a PathBui lder S24x, 2 6x, and 27x s witch for Translational Bridging, refer to the configuration example in the next section.

Configuration Examples

Figure 18 shows an example of a PathBuilder S24x, 26x, and 27x swit ch co nfi gur ed for Translational Bridging between an Ethernet and Token Ring Network within the same node. The records and parameters that need to be configured for Translational Bridging are shown.

Note

In this example, the parameters in Bridge Link 1 and Bridge Link 2 records remain at their default values. However, to implement the default settings, you need to call up the records (from the CTP) and then save them.

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Station A Station B

Port 13

Bridge Link 1

Transparent

Bridge Link 5

Bridge

PB S200 Switch

LCON

PVC

LCON

Bridge Link 6

Source Bridge

Bridge Link 2

Port 19

Ethernet

Port 13

Port Type: ETH Bridge Link Number: 1

Bridge Link 5

Bridge Type: TB

LAN Connection 1

LAN Forwarder Type: BRID Bridge Link Number: 5

Port 19

Port Type: TR Ring Number: 1 Bridge Link Number: 2

Bridge Link 6

Bridge Type: SR Link Mode: TRANS Virtual Ring Number: 2

LAN Connection 2

LAN Forwarder Type: BRID Bridge Link Number: 6

Network Services PVC Setup Table

Source: LCON-1 Destination: LCON-2

Token Ring

Figure 18. Translational Bridging Example

Figure 19 shows a situation where a PathBuilder S24x, 26x, and 27x switch is configured for tra nslational bri dging with SVCs/ PVCs originati ng from two re motes. Multiple remote Ethernet and Token Ring LANs may attach to the local Token Ring via the PathBuilder S24x, 26x, and 27x switch with Translational Bridging.

Port 13

Station A

Ethernet

Bridge Link 1

Transparent

Bridge

PB S200/Node 100

Bridge Link 5

LCON

X.25/FR Annex G

PB S200 Switch w/Translational

Node 200

Bridge Link 5

LCON

Bridge Link 1

Source Bridge

SVC

Port 13

Port Type: ETH Bridge Link Number: 1

Bridge Link 5

Bridge Type: TB

LAN Connection 1

LAN Forwarder Type: BRIDG Bridge Link Number: 5 Remote ID: 1

LAN Connection 1

LAN Forwarder Type: BRID Bridge Link Number: 5

Port 19

Port Type: TR Ring Number: 1 Bridge Link Number: 1

Bridge Link 5

Bridge Type: SR Link Mode: TRANS Virtual Ring Number: 2

Figure 19. Translational Bridging Point-to-Point Example

Port 13

Station B

Token Ring

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Bridge Frame Handling

Introduction This section summarizes how PathBuilder S200 series switches handle frames

during Source Route Bridge operation.

How Frame Handling Works

Broadcast Frame Handling

Once a PathBuilder S200 series switch station connected to a Token Ring and is operating normally, non-MAC frames are copied from the ring as they pass through the bridge station only if they satisfy these requirements:

• The Routing Information Present bit must be set in the source MAC Address of the frame.

• If the frame is non-broadcast, the local ring number, bridge number, and remote ring number must match the bridge's stored values for these numbers, and the routing field must have less than 7 to 14 LAN/bridge couplets (depending on the configured maximum allowed).

• If the frame is si ngle r oute b roadca st and f or warding of single route br oadcast is enabled, t hen the Routing Information field must not contain the remo te ring number since the frame has already been on the forward ring. If single route broadcast is disabled, the frame is not copied.

• If the frame is All Route Broadcast, then the Routing Information field must not contain the remote ring number.

These rules apply t o frames with ei ther l oca lly or univer sall y admi nist ered ad dre sses and for frames with either individual or group addresses.

When the All Route Broadca st frame is received from the LAN and initiated by another device on the LAN, it is sent to all remote bridges on all SVCs.

The single route broadcast frame is sent only to the remote bridge that is part of the spanning tree. The specific route frame is sent to the remote bridge via the single SVC that connects the bridges.

When received from the WAN, broadcast frames are sent to the Token Ring. They are sent to the other SVCs for general or spanning tree distribution, as appropriate, after the LAN port removes the frame from th e local ring.

Routed Frame Handling

When a specifically routed frame is received from the WAN, it is sent to the Token Ring if the next bridge li sted i n the Rout ing Inf ormatio n fiel d does not correspond to a bridge formed by a local SVC. Otherwise, it is forwarded to the proper SVC for additional bridgi ng with out be ing se nt t o the LAN. This keeps trans it t raf fi c of f rings where it can be avoided.

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Configuring Source Route Bridging Operation

Introduction Y ou configure a no de for Source Rout e Bridging dur ing normal bridge c onfigurati on.

Refer to “Configuring the PathBuilder S200 Series Switch for Bridging Operation” section on page 21 for more details.

This section provides some gui delin es you shoul d conside r when configur ing a node for Source Route Bridge operation.

Configuring the Node for SRB Operation

Individual Bridge Links

The Node must be enabled for Bridge operation and some general parameters established in the “Software Key” and “Node Record” sections of the configuration menu.

• Make sure the CSK is entered for Source Route Bridging (SRB).

• The subaddress within the node for the bridge module should be specified. This allows the bridge connections to other nodes to be targeted to the right subaddress upon entering the node.

• A Codex Proprietary Protocol ID must be specified in the Node Record to ensure that calls for other traffic types, if mistakenly connected to the bridge subaddress, are rejected. Only similar remote bridges must identify themselves with this ID.

For details on configuring the Node record, refer to the PathBuilder S200 Series Basic Protocols.

Once you complete node and port configuration, individual bridge links to other nodes must be established, up to a maximum of 32 per node. Figure 20 shows LAN/ WAN Bridge Links used in a PathBuilder S200 series switch LAN network.

WAN Bridge Link-Numbered 5 to 36 for 32 possible WAN Links. One link for each connection to a remote half bridge.

WAN

Adapter

Port-X.25, MX.25, FR or XDLC

WAN

Network

Token

Ring LAN

LAN Bridge LinkNumbered 1, only 1 link is operational.

Port

LAN

Port

LAN

Bridge

5 6 7 8 9

SVCs-Connect each half bridge across the WAN to a remote ha lf bridge.

Figure 20. LAN/WAN Bridge Links Used in PathBuilder S200 Series Switch LAN Network

To assist you in configuring the node, the LAN bridge-oriented parameters are considered separate from the WAN-oriented parameters:

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• LAN Side: The LAN port connection consists of one link. To configure the bridge module requires that you configure the LAN Port; the LAN Bridge; and the LAN Bridge Link, which passes the LAN traf fic from the LAN Port to the LAN Bri dge (always numbered “1”).

• WAN Side: The WAN Adapter (default subaddress 94) is used to make the transition from the LAN to the WAN. The WAN links are numbered 5 to 36 and provide up to 32 WAN connection links which correspond to potential bridges. These links pass the LAN traffic from the LAN Bridge to the WAN Adapter. Refer to the sections on Bridge software modules and links for mor e information.

• WAN Adapter: The WAN Adapter adapts LAN traffic to WAN protocols. It also provides other WAN services for the bridge, s uch as est ablishing ne twork calls via a set of configurable records.

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Connecting a Station to a Server in Source Ro ute Bridging

Introduction The following is an example of the process involved in establishing a connection

between a station on one Token Ring LAN with a server on a remote Token Ring LAN for a Source Route Bridging operation.

Procedure These steps describes the process of how a a station to server connection is set up:

1) The PC station (sour ce) on LAN AAA r equests a s ession t o a serve r (dest ination)

located on remote LAN CCC (Figure 21).

LAN AAA

PB S200

Bridge

WAN

Network

PB S200

Bridge

PB S200

Bridge

PB S200

Bridge

LAN

xxx

Server

LAN CCC

LAN

zzz

Figure 21. Example of a Station to Server Configuration

2) The PC assumes the server i s on t he loc al LAN, and t he PC sends an LLC frame

(typically an LLC1 TEST frame) around its local LAN AAA looking for a response from the server. The TEST frame has a destination MAC Address equal to the server’s MAC Address. Since the server is not on the local ring, no station responds to the server’s destination MAC Address (Figure 22). This TEST frame does not have the Routing I nformatio n Indi cator bi t (RII) set (t he high or der bit in the Source MAC Address) and as a r esult, it does not build a Rou ting Informat ion Field (RIF) to trace the path to the destination.

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Frame

LAN

AAA

PB S200

Figure 22. Server’s Destination MAC Address Not on LAN AAA

3) After receiving no response on the local LAN, the PC uses Source Route

Bridging (SRB) to find the path to the remote server. The PC can resend the TEST frame indicating that the frame is to be bridged over all routes. The PC resends an All Route Explorer (ARE) TEST frame via its SRB software (Figure 23).

LAN

AAA

ARE Frame

PB S200

Figure 23. All Route Explorer (ARE) Frame Searches the Network for the Server

4) The TEST frame includes the following:

• Destination Address is server's MAC Address.

• Routing Information Indicator bit (RII) is set to one. This bit is the mo st significant bit in the source address, indicating this frame has a Routing Information Field (RIF).

• Three bit s in the Routi ng Information Field (RI F) indicate th is is an ARE. This instru cts all bridges that enco unter this frame to forward the frame to their destination LANs. This form of broadcast ensures that at least one copy of the frame arrives at the destination.

• Routing Information Field (RIF) shows the path (LAN number/Bridge number, LAN number/Bridge number, etc.) that each ARE frame took on its search between the source and the destination.

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5) The PathBuilder S200 series switch transfers a copy of the ARE frame from the

LAN Port across LAN Bridge Link number 1 to the Bridge (Figur e 24). Since the frame is an All Routes Explorer, the Bridge broadcasts the frame across each of the existing WAN Bridge Links (32 max) to the WAN Adapter module.

6) The WAN Adapter transmits each ARE frame to a separate, already established

SVC which connects it across the WAN to a remote node (Figure 25). Note that in the node attached to LAN AAA, three bridge links (5, 6, and 7) to the WAN side are necessary because they go to the three remote LANs to establish complete bridges to thos e LANs. The three right-hand node s really need only one WAN Bridge Link each, but two additional ones are shown; they could be attached to other bridges in other nodes not shown.

LAN Bridge Link

LAN AAA

Port

Bridge

WAN Bridge Links

WAN

Adaptor

ARE Frame

WAN

Port

SVCs (PVCs for Frame Relay)

Figure 24. PathBuilder S200 Series Switch Transfers a Copy of ARE Frame to the Bridge Module

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PB S200

Bridge

WAN

Adaptor

LAN

Port

LAN

xxx

LAN AAA

PB S200

LAN

Port

WAN Bridge Link

PB S200

Bridge

WAN

Adaptor

WAN

Network LAN

WAN

Adaptor

Bridge

LAN

Port

LAN Bridge Link

PB S200

Bridge

WAN

Adaptor

LAN

Port

Figure 25. WAN Adapter Transmits Each ARE Frame Across the WAN

Server

CCC

LAN

zzz

7) One of the ARE frames finds the des tinatio n server, and the server recognizes the

MAC address in the TEST frame.

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8) The server issues a Specific Route TEST frame (also called a non-broadcast

frame) in response using the route indicated in the ARE TEST frame. Note that the server does not have to b roadcast (use ARE) t o get the TEST re sponse bac k to the PC; it uses a Specifically Routed TEST frame (Figure 26).

LAN AAA

PB S200

LAN

Port

PB S200

Bridge

WAN

Adaptor

WAN

Network

WAN

Adaptor

LAN

Port

Figure 26. Server Responds with Specifically Routed TEST Frame

9) The response TEST frame also has a Routing Information Field (RIF) with the

same path trace as the o rigin al ARE TEST fr ame exce pt the Di rect ion bit is se t to

1. This reverses the direction in which the RIF sequence is read and indicates the path back to the source. The RIF also se ts three bit s in the Routing Type field that indicate the frame is to be specifically routed and not broadcast.

10) When the response TEST frame reaches the source PC, the PC now knows what

route to use to send its frames to the server.

Server

LAN CCC

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Attaching a Station to a Ring

This table describes how a station attaches to a ring.

Step Action Result/Description

1 The station requests values for the

ring’s operational parameters from the RPS.

2 An attaching station also sends the

RPS its adapter software level as well as its Upstream Neighbor Address.

If... Then...

An RPS is present on the ring,

It responds to the station’s request by

The RPS then notifies the LAN managers that a new station has

attached to the ring. sending it the current values for the ring’s operational parameters.

An RPS is not present on the ring,

The ring station uses the values assigned by the

An RPS has a functional address of

C00000000002. program using

the ring station or the default values for its operational parameters.

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Transparent Bridging for Ethernet LANs

T ransparent Bridging for Ethernet LANs

Introduction A transparent bridge, also known as a spanning tree bridge, decides where to relay

Ethernet LAN frames by using the spanning tree protocol to develop and maintain a loop-free topology.

Using spanning tree, you can add a bridge anywhere in the Ethernet LAN without creating loops. The networ k de vic es a re not i nvol ve d in t hi s dec is ion pro ces s, whi ch is transparent to them.

Learning A transpar ent bridge monitors Ethernet LAN traffic, “learns” th e source address of

each frame it receives, and maintains a database (also known as the Forwarder) of source addresses and associated bridge connections. A transparent bridge uses a timeout process to purge its database of what it considers inactive addresses.

For the PathBuilder S200 seri es sw itch t o “le arn” wher e MAC st atio ns are loc ated i n relation to themselves, they use a ha rdware accel erator, a transparen t bridging forwarder, and a transparent bridging forwarding table.

A transparent bridge learns based upon the MAC source address. This address is placed into the transparent bridging forwarder table, along with the link that the PathBuilder S200 series switch received the frame on, if the address is not to be filtered.

Tr ansparent Bridge Forwarder

When a transparent bridge receives a frame, it checks its database fo r the frame address and performs one of the following actions:

• If the frame’s MAC destination address is not found in the TB forwarding table, then the bridge s ends the frame on all b ridge co nnections (excep t for the connection on which it arrived).

• If the bridge has learned the destination address, meaning the frame’s MAC destination address i s found in th e TB forwarding t able, the n the fra me is sent out on the learned link, unless there is a filter set on the link.

• The Hardware Accelerator discards local traffic before it reaches the node.

The Forwarder initiates the Learning process of the transparent bridge logic for frames received from the LAN and WAN ports.

After receiving an Ethernet frame, the Forwarder applies bridging logic, routes the frame to the appro priate Handler , and s ends the frame to t he outgoi ng link, which is a path to the frame’s MAC destination address.

The Forwarder:

• Initiates WAN frame learning

• Initiates LAN frame learning

• Filters the frame using the filtering facility

Information sent to the Hardware Accelerator includes:

• Source address

• Destination address

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Tr ansparent Bridge Forwarder Example

A frame arrives at the

TB Forwarder.

YES

the MAC

Source Address in the

forwarding

table?

YES

the MAC

Destination Address in

the forwarding

table?

YES

TB Forwarder checks

if any filters are set.

Figure 27 shows how the Forwarder and the Hardware Accelerator process a frame.

Drop

the frame.

YES

TB Forwarder checks

if any filters are set.

YES

filters

match?

filters

match?

flag for a Unicast or

Source Address on the

Permanent Station

the inbound

Multicast frame

set?

YES

the MAC

Address

List?

Drop

the frame.

YES

Learn the Source

Address.

TB Forwarder gives the

frame to the appropriate

handler as found in the

forwarding table.

Forwarder Statistics

filters

match?

YES

Drop

the frame.

TB Forwarder gives the

frame to the handlers

that are in the

forwarding state.

Handler sends

the frame.

Figure 27. How the Forwarder and Hardware Accelerator Process a Frame

In addition, the Forwarder collects the following types of statistics:

• Filtering

• LAN link

• WAN link

• Link error

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Forwarder/ Hardware Accelerator and LAN/WAN Handler s

Hardware Accelerator Functions

Figure 28 shows the relationship of the Forwarder and Hardware Accelerator to the LAN and WAN Handlers.

LAN

Handler TB

Forwarder

Accelerator

WAN

Handler

36 32

Figure 28. Relationship of Forwarder and Hardware Accelerator to LAN and WAN Handlers

The Hardware Accelerator performs these functions:

• Discards local traffic before it reaches the node

• Participates in the learning process for LAN traffic

• Participates in the aging process for LAN traffic

The Hardware Accelerator applies the aging process to the learned addresses on a LAN port. It needs to:

• Set the agin g timer bit for each address learned on the LAN link.

• Reset the aging timer bit fo r the entr y whene ver a frame wit h the same sour ce address passes through the bridge

• Decrement the aging timer bit when it receives periodic timeout notification from the Forwarder

• Remove all the aged-out entries from the Hardware Accelera tor database

The statistics which show the number of local traffic frames discarded by the Hardware Accelerator are displayed on the LAN port Statistic CTP menu.

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Transparent Bridging for Ethernet LANs

Forwarder Functions

The Forwarder bridging logic includes decisions such as:

• Which Link(s) the frame should be sent to.

If the destin ation addre ss of t he fr ame exi sts i n the Fo rwardi ng Table, and there is a link number associated with it, then the Forwar der checks whethe r filter s should be applied to the frame and cause the frame to be dropped. If all these conditions are satisfied and no filters apply, the Frame is sent over to the link via the Handler.

• Whether the frame should be broadcast to all ports, even though the frame is not a multicast or broadcast frame.

If the destination address of the frame did not exist in the Forwarding Table (such as when thi s is the first ti me t he bridge learns t he sour ce address of t he frame), the Forward er attempts to send the frame out over all links which are in Forwarding state (except the link wher e the fr ame arri ved). Befor e the Forw arder se nds the f rame out, it also checks whether filters are to be applied to this frame. The frame may get filtered at certain links.

• Whether the frame is a multicast or broadcast frame, and if it is, to which links the frame should be sent out.

The Forwarder attempts to send the multicast or broadcast frame over to all links which are in forwarding state (except the link where the frame arrived). Before sending the frame out t o each link, the For war der checks with the fi lt ering facilit y t o see if filters are to be applied to the frame at that link. If not, the Forwarder sends the frame over to the link. A multicast/Broadcast frame is a frame with the Least Significant Bit of its destination address being set to 1.

• Whether the received non-multicast and non-broadcast frame should be dropped without sending it out.

The Forwarder drops the fr ame due t o filte ri ng, when the link is unconfigured or the link is not in forwarding state.

Forwarder Initialization

Two types of forwarding database entries that are kept in running memory are:

• Learned (dynamic)

• Permanent (static)

The learned entries of the forwarding database are obtained from the source address of frames that are received by the bridge entity. This relies on the end stations sending frames so that the bridge learns the station location from the source address contained in the frame.

The permanent entries are obtai ned fr om a CMEM r ecord that is c onf igurable by the system administrator. They are loaded into the database whenever the node or the table is booted. The permanent entries are maintained by the system administrator.

During Forwarder Module initialization, the Forwarder creates the sockets to connect to other modules in the node, such as sockets used to communicate with the network handlers. It also defines MACRO services in the Forwarder Module Descriptor to export the socket addresses to the outside world.

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Forwarder and STPE

The Forwarder cleans up al l entrie s in the Forw arding Table when there are spanning tree topology changes taking place. These actions are considered services the Forwarder provides to the Spanning Tree Protocol Entity (STPE). The Forwarder provides these services through MACRO routines so that they are accessible to the entire system.

Note

The Forwarder is not required to pass STPE traffic to the handlers. The STPE is considered to be an independent entity a nd similar to all the forwarders in the system. It has its own interface with the network handlers and it uses this interface passing PDUs to the network via the handlers. For example, it forwards Spanning tree PDUs directly to the handler and does not go through the Forwarder.

Learn Only Period The Learn Only Period is a ti mer you can set fr om the CTP. This timer is started

whenever the node boots. Until thi s timer expires, the bridges learn onl y LAN station addresses and place them into the forwarding database. The bridges do not forward any frames during this interval. When the timer expires, the bridges forward frames in the usual w ay. The default setting for t his parameter is 10 seconds.

This timer is not to be confused with the Forward Delay timer of the spanning tree protocol entity (STPE). The STPE timer is used to control how long a bridge link withholds a link from going into the forward state once it is determined that the link should be part of the spanning tree. This timer is set to avoid bridge topology loops from forming. The Learn Only Period timer prevents the bridge from sending broadcasts (as par t of t he lea rning pr ocess ) whe n the br idge f irst c omes up, and has a sparse forwarding database.

Aging Aging is an important process associated with the learned da tabase entrie s. When a

new entry is learned and placed in the forwarding database, a timer is set that indicates the station with the MAC address is still active. If the timer expires for an entry, the entry is removed from the database. The aging time for learned entries in the forwarding table is configurable by the system administrator. This parameter is located in the Bri dge Parame ters me nu. The def ault set ting for this para meter i s 3600 seconds (1 hour).

The Forwarder starts the Aging Timer for the learned addresses in the Forwarding Table.

The purpose for aging database entries is to allow changes in the network configuration t o be auto matica lly accou nted fo r in t he forwar ding t able. If a stati on is moved from one LAN to another, the station becomes reachable when the entry ages out and is replaced with a new entry that indicates new forwarding information.

Aging does not apply to the per manen t en trie s in the forw ardin g table . The se entr ies are maintained by the sys tem admini stra tor and kept in CMEM. They are never ag ed out of the forwarding database and they are never corrected. If a frame arrives on an unexpected link with a source address in the permanent part of the forwarding table, the table is not changed.

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Transparent Bridging for Ethernet LANs

Forwarder Database and Spanning Tree

How They Work Together

There is a close relationshi p bet w een the f orwa rdi ng dat ab ase and the spanning tree. The spanning tree can be ma nually conf igured. This is a reasonab le thin g to do in the case where a stable environment exists since it saves CPU processing by eliminating aging timers and the broadcasting that is employed when the forwarding table does not have a suitable entry. In this case, when the node is booted, bridges will form a spanning tree (always the same one provided all equipment remains operational), and a permanent forwardi ng data base ca n be lo aded from CMEM that is re quired for the configuration. This also allows a quick method for the bridge to become operational.

The learning process continues even if the forwarding table is formed initially from permanent CMEM entries. That is, the forwarding database adds learned entries as they occur; if there are stations active that are not in the initial database, they will be added as they are learned. Such an expanded database can be written to the CMEM by a CTP update command. This has the effect of converting the entire forwarding table in runnin g memor y t o p ermanent entries and creating a new per m anen t table in CMEM equal to the running configuration.

If the spanning tree is configured for automatic configuration, then the operation of the forwarding database is as noted previously. The permanent database offers a means of quickly obtaining a forwarding database without the bridge having to broadcast frames for whi ch it doe s not know t he desti nati on link . However, since the bridge topology can change in an unpredi ctable way (correspondi ng to unpredi ctable network failures), it is best that the entries in the database ar e all aged. Aging all entries allows the forwarding database to remain current even with topology changes. Therefore, it is re commended that if such change s are expected, the syst em administrator should not use permanent forwarding entries. However, there is no reason that they canno t be use d, and th e fu ll se t of edi ting and s aving c ommands s till apply when the spanning tree is in automatic operation.

Deleting Forwarding Table Entries

Forwarding table entries can be deleted from CMEM by CTP command. If the system administrator change s the t opolog y (cha nges br idges o r sta tions), t he CMEM record (edit, delete, add) can be updated and the table booted to get a cleaned up version of the database in working memory. This boot does not disrupt bridge operation other than a momentary disruption to forwarding traffic.

The entire forwarding table in CMEM can also be deleted by a single CTP command. This lets you make substantial changes to the topology, then boot the bridge network (with no permanent forwarding table entries) to let the bridge learn station locations. After a suitable learning time, you can update the entries to permanent CMEM entries using the update command. From that point on, the permanent forwarding table will contain valid entries for the configuration.

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Using Filters

Support The Forwarder provide s its own fil tering faci lity whic h is used to red uce unneces sary

traffic and to provide security. The filtering facility supports the following types of filters:

• Incoming Source Address Filter

• Incoming Destination Address Filter

• Outgoing Source Address Filter

• Outgoing Destination Address Filter

Incoming Source Address Filter

Incoming Destination Address Filter

Outgoing Source Address Filter

Outgoing Destination Address Filter

Unicast Link Protect Flag

The Incoming Source Address Filte r fil ters pac kets ar e base d on thei r sour ce addr ess and incoming links. Frames with a source address found in the Incoming Source Address Filter List are discarded without applying bridge logic. This filter may be applied to all links or selected links.

The Incoming Destination Address Filter filters packets based on their destination address and the incoming ports. Frames with a destination address found in the Incoming Destination Address Filter List are discarded without applying bridge logic. This filter may be applied to all links or selected links.

The Outgoing Source Addres s Filte r filters packets b ased on th eir sour ce address and the outgoing links. Frames with a source address found in the Outgoing Source Address Filter List are discarded. This filter may be applied to all links or selected links.

The Outgoing Destination Address Filter filters packets based on their destination address and the outgoing links. Frames with a destination address found in the Outgoing Destination Addres s Filte r List are disc arded. Thi s filt er may be appli ed to all links or selected links.

When a frame comes from a link with the Unicast Link Protect Flag set, and if its source address is not found in the Permanent Station Address list, the frame is dropped.

When a frame is being sent out over a link with the Unicast Link Protect Flag set, and if its destination address is not found in the Permanent Station Address List, the frame is dropped.

Once the Unicast Link Protect Flag is set for a link, source address learnin g for Unicast frames is sto pped for that link and al l th e addr esses that were lear ned be for e are moved into the Permanent Station Address List.

Setting or Clearing of Unicast Link Protect Flag is performed via the LAN Control menu located in the Main menu.

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Transparent Bridging for Ethernet LANs

Multicast Link Protect Flag

When a multicast/br oad cast frame comes fr om a l in k wit h t he Multicast Protect Flag set, and if its source address is not found in the Permanent Station Address list, the frame is dropped.

When a multicast/broadcast frame is sent out over a link with the Multicast Protect Flag set, and if its destinati on ad dress is not found in the Permanent Station Address List, the frame is dropped.

Once the Multicast Protect Flag is set for a link, source address learning for multicast/broadcast frames is stopped for that link totally and all the addresses that were learned before are moved into the Permanent Station Address List.

Setting or Clearing of Multicast Link Protect Flag is performed using the LAN Control menu located in the Main menu.

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T ransparent Bridge Co nfiguration Parameters

TB Forwarding

Figure 29 shows the Transparent Bridge Forwarding Ta ble parameters.

Table

Node: Address Date: Time: Menu: Configure Bridge Path:

Bridge Parameters Bridge Link Parameters MAC Address Filter Table Protocol Filter Table NETBIOS Name LSS Parameters TB Forwarding Table

Entry Number *Local MAC Address *Bridge Link Number

Figure 29. Transparent Bridge (TB) Forwarding Table Menu

Parameters These parameters make up the Transparent Bridge Forwarding menu.

Entry Number

Range: 1 to 8000 Default: 1 Description Entry used to reference this table record.

*Local MAC Address

Range: 00-00-00-00-00-01 to FF-FF-FF-FF-FF-FF Default: 00-00-00-00-00-01 Description MAC Address that is to be used for forwarding.

Bridge Link Number

Range: 1, 5 to 36, Default: 1 Description The bridge link to forward a frame with the associated MAC

Address.

Boot Type: Perform a node boot to implement changes to this parameter.

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Bridge Filtering

What is It? Bridge filtering prevents extraneous traffic from traversing the WAN and stops the

unintentional proliferation of traffic onto other remote LAN segments. In Ethernet T ran sparen t Bridgin g, the broa dcast fe ature lets st ations d etermine routes

to other end stations. Broadcasting to the entire network can unnecessarily degrade performance becau se of b roa dcasts traversing LAN s egme nts that are not in any part of the network where the target station resides.

Therefore, you can use bridge filtering methods such as MAC Address Filtering, Protocol Filtering, and NetBIOS Name Filtering to control broadcast traffic and reduce overhead.

How Filtering is Used

Filtering is used to:

•Reduce Filtering broadcasts can help to reduce this overhead.

• Control the unnecessary proliferation of application level broadcasting used on Novell and NetBIOS applications.

• Restrict access to certain LAN segments for security reasons.

• Prevent unnecessary traffic from proliferating onto the WAN where bandwidth is limited. This can help to reduce congestion and minimize delay for traffic that must cross the WAN.

• Prevent stations usi ng a certain pr otocol from oper ating ou tside thei r intended scope. Protocol formats that are filtered include DSAP and SNAP.

You can filter the MAC address contained in a frame or a protocol. The system applies MAC address filtering first and then follows with protocol filtering if appropriate.

MAC Address filtering can be performed on either the source address or destination address.

unnecessary traffic affecting the performance of LAN segments.

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MAC Address Filtering

What Is It? This feature lets you filter bridge traffic based on MAC address.

The Bridge Link Table and the MAC Address Filter Table are used to configure MAC Address filtering.

The Bridge Link Table specifies:

• Whether or not any filtering action is to be performed.

• The filtering action to perform when the MAC frame address is not found in the MAC Address Filter Table.

The Bridge Link Table contains these parameters, including the MAC Address Filtering Action parameter, which lets you specify the filtering actions to be applied at the bridge link. These parameters are located under the Configure Bridge Link menu selection:

• Entry Number

• Bridge ID

• Hop Count Limit

• Largest Frame Size

• MAC Address Filter Action

• Protocol Filter Action

• STPE Link State

• STPE Priority

• STPE Path Cost

MAC Address Filter Table Parameters

The MAC Address Filter Table specifies:

• The MAC Address of the frame to be filtered.

• The filtering action to perform on the frame.

This table is used in conjunction with the Bridge Link Table to specify filtering action and includes the link action parameters which allow you to apply filtering action to every link.

This table describes the MAC Address Filter Table parameters.

Parameter Action

MAC Address Frames that have MAC Addresses matching this MAC

Address are filtered as specified by the parameters in this table.

Incoming Source Address Link Action

Outgoing Source Address Link Action

Incoming Destination Address Link Action

Perform filtering action on an inbound frame having the indicated MAC Source address.

Perform filtering action on an outbound frame having the indicated MAC Source address.

Perform filtering action on an inbound frame for the indicated MAC Destination address.

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Parameter Action (continued)

Bridge Filtering

MAC Address Filtering Action Parameter Selections

Outgoing Destination Address

Perform filtering action on an outbound frame for the indicated MAC Destination address.

Link Action List of Links Sp ecifi es t he li nks a ssoci ated with t he pr ecedi ng li nk act io n

parameters in this ta ble. When Pass list (PL) is spec ified, the associated listed links pass the frame and the unlisted links block it. Conversely, when Blocklist (BL) is sp ecified, the associated list ed links block the frame and the unlist ed links pass it.

This table lists the filtering actions available for the MAC Address Filtering Action parameter.

Parameter

Action

Value

Pass (P) Look in th e MAC Address F ilter Table for an entry with a matchi ng

MAC frame address and perform the filtering action specified by this entry. If no matching MAC frame address is found, pass the frame.

Block (B) Look in the MAC Addres s Filter Table for an entry with a matching

MAC frame address and perform the filtering action specified by this entry. If no matching MAC frame address is found, block the frame.

What Happens During Filtering

None (N) No filtering to be performed; pass the frame.

When filtering is performed, the system checks the Bridge Link Table of the bridge link involved with the frame to se e if the MAC Address Filtering Act ion parameter is configured to disable all filtering on that bridge link. Figure 30 shows the process involved in MAC Address filtering.

If the parameter is configu red t o d is able filtering ( NONE selected), then the frame is allowed to pass and no filtering is applied.

If the parameter is configured with another value, either PASS or BLOCK, this signifies that the MAC Address Filter Table is to be checked to determine whether filtering action is to be performed. In this situation, the frame is checked to see if a match occurs between the MAC address in the frame and an address contained in an entry in the MAC Address Filter Table.

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MAC Filtering Process

Figure 30 shows the MAC Filtering process.

Check Bridge

Link Record or Entry

NONE

Pass frame

without filtering

Apply Table Filter:

PASS or

BLOCK

YES

MAC Address

Filtering Action

Setting?

PASS or BLOCK

Check MAC Address Filter Table for match

of frame MAC Address

Frame MAC

Address in MAC

Address Filter

Table?

Check Bridge

Link Table

MAC Address

Filtering Action

Setting?

PASS

Pass the

frame

BLOCK

Block the

frame

Figure 30. MAC Address Filtering Action

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Bridge Filtering

Mac Filtering Process

Incoming and Outgoing Frames

As shown in Figure 30, if a match is detected, the system applies the filtering action configured for that e ntry. The filtering action is to either PASS the frame or BLOCK the frame for all links or for a configured list of links. This filtering action overrides the action specified in the MAC Address Fil ter Action para meter.

If there is no match between the frame MAC Address and any entry in the MAC Address Filter T able, then filtering action on that frame is not controlled by the MAC Address Filter Table.

When the filtering action is not controlled by the MAC Address Filter Table, the action taken by the bridge is determined by the MAC Address Filter Action parameter in the Bridge Link Table; the action is to either PASS the frame or BLOCK it.

The MAC Address Filter Action parameter determines if the filter table is enabled on a bridge link. This same parameter is used to define the action taken (PASS or BLOCK) when no match is made in the MAC Address Filter Table.

For a detailed description of the MAC Addre ss Filter parameters, refer to

“Configuring the MAC Address Filter Table” section on page 66.”

The filtering actio n is appli ed to each l ink. The frames pas sing on a li nk can be ei ther incoming or outgoing (see Figure 31). Incoming means that the frame is entering the bridge from elsewhere either from the LAN or WAN. Outgoing means the frame is leaving the bridge. Therefore, a given frame can be incoming on one link and outgoing on another link (provided it does not get blocked due to filtering). Filtering can be applied at each of those links.

For any link, the PASS or BLOCK attribute can be set for either the source address or the destination address. This method allows you to individually configure every combination of i n/out and sourc e/desti nation t o eithe r a p ass or a block a ction f or any link.

Bridge Links

Token Ring 1

Outgoing Frame

(from Bridge)

Frames passing on a link can be either incoming or outgoing. The same frame can be inc oming on one link and outgoing on another lin k.

Bridge

Incoming Frame

(to Bridge)

WAN

Network

Figure 31. Example of a Frame Passing on a Bridge Link

The source address (incoming or outgoing) refers to the frame having the indicated MAC source address. The destination address (incoming or outgoing) refers to the frame havi ng the indica ted MAC destination addr ess.

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MAC Address Filtering Examples

Introduction This section shows two filtering examples. Figure 32 shows how the source address

can be used to fil ter fr ames. Fig ure 35 shows how the MAC Address Filter Table can be used to filter frames by combining multiple source and destination addresses.

First Example In Figure 32, the source address (MAC Address represented by A) is used to filter

frames passing in or out of the bridge via links 1, 5, and 6 (Figure 32). Frames originating from the station with MAC Address A are to be sent to server B but not server C. Figure 32 shows that for bridge link 1, Incoming Source Address frames with MAC Address A are passed, and Outgoing Source Address frames with MAC Address A are passed on link 5, but blocked on link 6.

Source Address

PB S200

Token Ring 2

Token Ring 3

Token Ring 1

Incoming

Source

Pass

Bridge

Pass

Outgoing

Source

Outgoing

Source

Block

PB S200

How To Configure the Example in Figure 32

Incoming Sour c e Address: Pass Link 1 Outgoing Source Address: Pass Link 5; Do Not Pass L ink 6 (Block)

Figure 32. Example of Bridge Links Configured to Filter Selected MAC Address Frames

T o configur e something s imilar to F igure 32, complete the Bridge Li nk record fo r the bridge and the MAC Address Filter Table as shown in these tables.

Configuring the Bridge Link Record

Parameter Values

Entry Number 156 MAC Address Filter Action Pass Pass Pass

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Bridge Filtering

Configuring the MAC Address Filter Table

Parameter Values

Entry Number 1 MAC Address A Incoming Source Address Action Passlist List of Links 1 Outgoing Source Address Action Passlist List of Links 5

In a Bridge Link Recor d, Pass (or Bl ock) tell s the syste m to check the MAC Addr ess Filter Table to find out what filtering t o perf orm. If t he Brid ge Link Record s pecif ied None, then the frame would pass without any filtering.

If the frame MAC Address is in the MAC Addre ss Filter Table, filtering is performed on the frame as specified in this table. The MAC Address Filter Table used in this example specifies the filtering to be performed on MAC Address A as the incoming source address to the bridge. Frames with Incoming Source Address A are passed at link 1 (see Figure 32). Frames with Outgoing Source Address A are passed at link 5 (to server B), but not passed on link 6 (to server C).

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Identifying Address Links for MAC A ddressing

Why it is Important Identifying the address links is an important step in configuring MAC Address

filtering. A Source Address link allows a device on the LAN to send frames. A Destination

Address link allows a device on the LAN to receive frames. The Incoming Source Address link provides a path for a f rame t o go f rom th e Token

Ring to the bridge. The Out goi ng Source Address link pro vide s a pat h for a frame to go from the bridge to the WAN.

The Incoming Destination Address link provides a path for a frame to go from the WAN to the bridge. The Outgoing Destination Address link provides a path for a frame to go from the bridge to the LAN.

Example of Address Links

Figure 33 shows that link 5 serves as both the Outgoing Source Address link and the Incoming Destination Addre ss link. In this exampl e, Outgoing Source Address link 5 allows the File Server with MAC Address 10:00:5A:00:00:40 (the source) to send frames to the WAN via li nk 5. Incoming Destination Address link 5 allows the File Server with MAC Address 10:00:5A:00:00:40 (the destination) to receive frames from the WAN via link 5.

Outgoing Source Address Link (MAC Address 10:00:5A:00:00:40) Incoming Destination Address Link (MAC Address 10:00:5A:00:00:40)

Incoming Source Address Link (MAC Address 10:00:5A:00:00:40) Outgoing Destination Address Link (MAC Address 10:00:5A:00:00:40)

Bridge

Node 100

Token

LAN

Ring 2

MAC Address 10:00:5A:00:00:40

File Server

Figure 33. Example of Address Links

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Bridge Filtering

MAC Wildcard Filtering

What Is It? MAC wildcard filtering is an enhancement to the Motorola Network Access

Products MAC Filter table. MAC wildcard filtering lets you configure the MAC

filter tables and use wildcards “*” to designate numeric pieces of the MAC address. The MAC Address filter lets you configure a table of MAC Address filters (each

filter contains a MAC address which is a string of 12 characters from the range 0-9, A-F). The table is searc hed for eac h incoming an d outgoing f rame on the LAN/ WAN link to find a match in the tab le for the MAC address in the frame.

This enhancement lets you use the wildcard character “*” in any of the 12 character positions while configuring a filter. The wildcard character matches any of the valid characters allowed in a MAC address (0-9, A-F) when it is used to filter a given MAC Address.

MAC wildcard filtering lets yo u config ure a smaller MAC Addr ess Fil ter ta ble if you configure MAC Address filters where one or more of the 12 character positions can be allowed to take any va lue in the permissible range.

For example, with the existing functionality, if the Bridge had to be configured to block all the frames with MAC addresses in the range 080004001F00 to 080004001FFF, you would have to configure 256 filters. Now you can simply specify 080004001F**.

PathBuilder S200 Series Switch Support

How MAC Wildcard Filtering works

PathBuilder S200 series swit ches support the MAC wildcard featur e on t he Et her net .

Figure 34 shows a typical MAC wildcard filtering application:

080004001F05

080004001F04

080004001F03

080004001F01

080004002F01

080004001F02

Figure 34. Example of How MAC Wildcard Filtering Works

With the old filtering system, if you do not want any of the devices shown on the LAN on the left to access the WAN, you would need to configure all five entries. With the MAC wildcard filtering, only one entry is required. For example, you can specify 080004001F** to pr event all devices from accessing the WAN.

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Configuring the MAC Address Filter Table

Introduction The MAC Address Filter Table controls which frames are allowed to pass on to

different link s and le ts you cont rol pro pri et ar y inf ormat i on tha t you may not want to go to another LAN. It is also useful in controlling the unnecessary proliferation of broadcast frames in the LAN network.

MAC Address Filter

Figure 35 shows the MAC Address Filter Table parameters.

Table Parameters

Node: Address: Date: Time: Menu: Configure Bridge Path:

Bridge Parameters Bridge Link Parameters MAC Address Filter Table

Entry Number MAC Address Incoming Source Address Link Action Outgoing Source Address Link Action Incoming Destination Address Link Action Outgoing Destination Address Link Action

Figure 35. MAC Address Filter Table Menu

Categories MAC Addresses can fall into four categories:

• Incoming Source

• Outgoing Source

• Incoming Destination

• Outgoing Destination

Every node (bridge) has one MAC Address Filter Table. Every bridge link can be configured to determine whether or not frames passing on that bridge link are to be filtered according to the entries in the MAC Address Filter Table.

The filter table is examined to see if there is a match. If a ma tch is found (table and frame), additional table parameters determine when to pass or block the frame. If there is no match, the decision is dependent upon the Bridge Link record to determine whether to pass or block.

Action is then taken on what is specified in this record (pass or block), rather than the filter table , when there is no match to an ent ry in this filter table.

Note

A Table boot is required to make MAC Address Filter parameters part of an active configuration. Booting is nondisruptive to data or call connections.

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Parameters These parameters make up the MAC Address Filter Table.

Entry Number

Range: 1 to 300 Default: 1 Description: Entry number used to reference this table record for filtering

action.

Note

If you do not wish to determine filter action for this link through the MAC Address Filter Table, select NONE in the Bridge Link record.

MAC Address

Range: 00-00-00-00-00-00 to FF-FF-FF-FF-FF-FF (Canonical) Default: 00-00-00-00-00-00

Bridge Filtering

Description: Frames with MAC Addresses that match this MAC Address are

filtered as specified in the following parameters. For an example

of MAC Address Filtering, refer to “MAC Address Filtering Examples” in this guide.

Incoming Source Address Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: Incoming source m eans th at the fram e is en terin g th e bridg e enti ty

from the LAN that includes the MAC address (the source). Therefore, a given source frame will be incomi ng from the LAN to the Bridge and outgoing from the Bridge to the WAN (provided it does not get blocked due to filtering). Refer to Figure 31.

• P ASS: Pass incoming f rames with thi s MAC Address val ue on all links that are referencing this table. If this value is chosen, skip the List of Links.

• BLOCK: Block incoming frames with this MAC Address value on all links tha t are ref erencing t his table . If thi s value is chosen, skip the List of Links.

• PASSLIST: If this value is used, a pass list is specified by the following parameter, List of Links. Links in this list pass the frame. Links not in this list block the frame.

• BLOCKLIST : I f t his value is used, a block list is spe ci fi ed by the parameter, List of Links. Links in this list block t he frame. Links not in this list pass the frame.

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Outgoing Source Address Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: Outgoing source m ea ns that the fr ame is leaving t he bridge for the

WAN. Therefore, a given source address frame will be outgoing from bridge to WAN and incoming from LAN to bridge (p rovided it does not get blocked due to filtering).

• PASS: Pass outgoing frames with thi s MAC Addres s val ue on all links that are referencing this table. If this value is chosen, skip the List of Links.

• BLOCK: Block outgoing frames with this MAC Address value on all links tha t are ref erencing t his table . If thi s value is chosen, skip the List of Links.

• PASSLIST: If this value is used, a pass list is specified by the following parameter, List of Links. Links in this list pass the frame. Links not in this list block the frame.

• BLOCKLIST : I f t his value is used, a block list is spe ci fi ed by the parameter, List of Links. Links in this list block t he frame. Links not in this list pass the frame.

Incoming Destination Address Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: A Destination Address link allows a device on a Token Ring to

receive frames. An Incoming Destination Address link provides a path for a frame to go from the WAN to th e bridge.

• P ASS: Pass incoming f rames with thi s MAC Address value on all links that are referencing this table. If this value is chosen, skip the List of Links.

• BLOCK: Block incoming frames with this MAC Address value on all links tha t are ref erencing t his table . If thi s value is chosen, skip the List of Links.

• PASSLIST: If this value is used, a pass filtering list is specified by the following parameter, List of Links. Links in this list pass the frame. Links not in this list block the frame.

• BLOCKLIST: If this value is used, a block filtering list is specified by the following parameter, List of Links. Links in this list block the frame. Links not in this list pass the frame.

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Outgoing Destination Address Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: The Outgoing Destinati on Address li nk provides a pat h for a fr ame

to go from the bridge to the LAN. It allows a device on a Token Ring to receive frames.

• PASS: Pass outgoing frames with thi s MAC Addres s val ue on all links that are referencing this table. If this value is chosen, this filter is fully configured and the next prompt would wrap to MAC Address to allow further config urati on of thi s reco rd. If this value is chosen skip the List of Links parameter.

• BLOCK: Block outgoing frames with this MAC Address value on all links tha t are ref erencing t his table . If thi s value is chosen, this filter is fully configured and the next prompt would wrap to MAC Address to al low further configurati on of this record. If this value is chosen, skip List of Links parameter.

• PASSLIST: If this value is used, a pass filtering list is specified by the parameter List of Links. Links in this list pass the frame. Links not in this list block the frame.

• BLOCKLIST: If this value is used, a block filtering list is specified by the parameter, List of Links. Links in this list block the frame. Links not in this list pass the frame.

List of Links

Range: 1,5, to 36 Default: (no entry) Description: Each entry is a bridge link number in the range 1, 5, to 36. The

individual numbers correspond to the links that filter according to the preceding parameter. If the preceding parameter is:

• PASSLIST: The listed links pass the frame and unlisted links block the frame.

• BLOCKLIST: The listed links block the frame and unlisted links pass the frame.

This parameter appears only when the parameter Outgoing Destination Address Link Action = PASSLIST or BLOCKLIST.

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Protocol Filtering

What is It? Protocol filtering is used to prevent nodes operating with a certain protocol from

operating outside their in tended scope. For proto col filt ering , the same fund amental s apply as with MAC Address Filtering except the Bridge Link record specifies Protocol Filtering Action.

This table shows how to configure the Bridge Link record for protocol filtering.

Parameter Values

Entry Number 1 5 6 Protocol Filtering Action Pass Pass Pass

When protocol filter ing is p erformed, t he system checks th e Bridge Li nk Table of the bridge link involved with the frame to see if the Protocol Filtering Action parameter is configured to disable all filtering on that bridge link.

Figure 30, which describes the MAC Address filtering process, is also applicable to protocol filtering. For example, if the parameter is configured to disable filtering (NONE selected), then the frame is allowed to pass and no filtering is applied.

The Protocol Filter Table is used with the Bridge Link Table to specify filtering action. It includes the link action parameters used to apply filtering action to every link.

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Configuring the Protoco l Filter Table

Introduction The Protocol Filter Table prevents stations operating with a certain protocol from

operating outside their intended scope. This filtering action is applied to that part of the frame that defines the protocol carried by the frame.

Note

A Table boot must be performed to implement changes to the Protocol Filter Table parameters.

Protocol Filter

Figure 36 shows the Protocol Filter Table parameters.

Table Parameters

Node: Address: Date: Time: Menu: Configure Bridge Path:

Bridge Parameters Bridge Link Parameters MAC Address Filter Table Protocol Filter Table

Entry Number Protocol Type Protocol Value Incoming Protocol Link Action Outgoing Protocol Link Action

Figure 36. Configure Protocol Filter Table Menu

Parameters These parameters make up the Protocol Filter Table Record.

Entry Number

Range: 1 to 100 Default: 1 Description: Entry number used to reference this table record.

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Protocol Type

Range: DSAP, SNAP Default: DSAP Description: Indicates what type of protocol is involved in the frame.

DSAP (Destination Service Access Point): The protocol value to be filtered is the Destination SAP field of the 802.2 LLC formatted frame. This type includes:

Protocol SAP (hex value)

Banyan BC (used only for 802.5) Novell IPX E0 (used only for 802.5) NetBIOS F0 ISO Connectionless Internet FE SNAP (Sub Network Access Protocol): The Protocol Value to be

filtered is specified by the SNAP header which identifies the 3-byte Organizationally Unique Identifier (OUI) and 2-byte Protocol Type used for the frame. This type includes:

Protocol OUI/IP (hex value)

AppleTalk Phase II 08-00-07-80-9B Apple ARP Phase II 00-00-00-80-F3 Proteon Proprietary AppleTalk

00-00-93-80-02

Phase I for F DDI Proteon Proprietary AppleTalk

00-00-93-80-02

ART Phase I for FDDI

Note

The protocols listed here represent only some of those that are currently available for DSAP and SNAP.

Protocol Value

Range: 00 to FF (If Protocol Type = DSAP)

0000000000 to FFFFFFFF (If Protocol Type = SNAP)

Default: 00 (If Protocol Type = DSAP)

0000000800 (If Protocol Type = SNAP)

Description: Indicates the hexadecimal value of the protocol that is filtered or

forwarded.

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Incoming Protocol Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: Specifies the action to be taken on the incoming protocol. These

actions include: PASS, BLOCK, PASSLIST, or BLOCKLIST.

• PASS: If this value is used, incoming frames with the specified protocol value are passed on all links. All other protocols are blocked on incoming links. If this value is chosen, skip the List of Links parameter.

• BLOCK: If this value is used, incoming frames with the specified protocol value are blocked on all links. All other protocols are passed o n incoming links . If this val ue is chosen, skip the List of Links parameter.

• PASSLIST: If this value is used, a pass list is specified by the List of Links parameter. Links in this list pass the frame. Links not in this list block the frame. An empty li st means all links will block.

• BLOCKLIST : I f t his value is used, a block list is spe ci fi ed by the List of Links parameter. Links in this list block the frame. Links not in this list pass the frame. An empty list means all links will pass.

Outgoing Protocol Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: Specifies the action to be taken on the outgoing protocol. These

actions include: PASS, BLOCK, PASSLIST, or BLOCKLIST.

• P ASS: If this value is used, out going frames with th e specified protocol value are passed on all links. All other protocols are blocked on outgoing links. If this value is chosen, skip the following parameter, List of Links.

• BLOCK: If this value is used, outgoing frames with the specified protocol value are blocked on all links. All other protocols are passed on outg oin g link s. If thi s valu e is c hosen, skip the following parame ter, List of Links.

• PA SSLIST: Pass list. If th is value is used, a pass filtering list is specified by th e following parameter, List of links. Links in this list pass the frame. Links not in this list block the frame.

• BLOCKLIST : Block list. If thi s value is used, a blo ck filtering list is specified by the following parameter, List of Links. Links in this list block the frame. Links not in this list pass the frame. An empty list means all links will pass.

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DSAP Values The DSAP is a 1-byte ID found in the LLC field (see Figure 37). You set this value

in the Protocol Value parameter of the Protocol Filter Table. Examples of DSAPs include:

• IBM (04, 08,...)

• Banyan Vines (BC)

• Novell IPX (E0)

• IBM NetBIOS (F0)

LLC Field

DSAP SSAP Control LLC Info

Figure 37. Protocol ID DSAP Located in LLC Field

SNAP Protocol ID The SNAP is five bytes and is also found in the LLC field. The first three bytes are

OUI and the last two bytes are the Protocol ID (Figure 38).

LLC Field

DSAP SSAP Control 5 Bytes

AA AA

AA = Indicates SNAP Format 03 = Unnumbered Information OUI = Organizationally Unique Identifier Type = 2-Byte Protoco l ID

OUI

00 00 00

Type

2 Bytes

Figure 38. SNAP Protocol ID

The SNAP format is used to identi fy Etherne t and pre-IEEE 802 pr otocol IDs that do not fit the 1-byte ID.

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Example of Protocol Filter Table

This table provides an overview of the Protocol Filter Table parameters.

Parameter Action(s)

Entry Number Used to reference th is table record. Protocol Type Indicates what type of protocol is involved in the frame.

Selections include: NONE, DSAP, and SNAP.

Protocol Value Indicates the value of the pr otocol that is filtered or

forwarded. Range: 00-0xFF (DSAP); 0000000000-FF... FF (SNAP).

Incoming Protocol Link Action

Outgoing Protocol Link Action

Specifies the action to take on the incoming protocol. Actions include: Pass, Block, Passlist, and Blocklist.

Specifies the action to take on the outgoing protocol. Actions include: Pass, Block, Passlist, and Blocklist.

List of Links Specifies the links assoc iated with t he prece ding lin k actio n

parameters in this ta ble. Whe n Passlist (PL) is spec ified, the associated listed links pass the frame and the unlisted links block it. Conversely, when Blocklist (BL) is specified, the associated listed links block the frame and t he unliste d links pass it.

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NetBIOS Name Filtering

Introduction The NetBIOS Name Filtering feature compares NetBIOS broadcasts to a “pattern”

that may have a wild card “*” cha rac te r a t t he e nd. For example, if all ser ve rs h ave a naming convention with the first part of the name the same, for example, “SVR...”, then you can complete only one entry in the NetBIOS Filter Table to permit broadcasts to and from the “SVR*” name pattern.

Example of NetBIOS Name Filtering

Figure 39 shows an example of how to configure NetBIOS Name Filtering in a T oken Rin g Source Rout Bri dging a pplic ation , however the sa me is true for Ether net Transparent Bridging.

Boston Branch Office

LAN LAN

Bridge Link 1

Bridge Link Parameters

NetBIOS Name Filter Action: Block

Bridge Link 5

NetBIOS Name Filter Table

String Type: ASCII NetBIOS Name HOME* Incoming NetBIOS Name

Link Action: PASS

Outgoing NetBIOS Name

Link Action PASS

WAN

Home Office

PB S200PB S200

HOME_FILE_01BOSTON_FILE_01

Figure 39. NetBIOS Name Filtering Configuration Example

What Is NetBIOS? Network Basic Input Output System (NetBIOS) is a session-level protocol

standardized by IBM that serves as one of the main Application Programming Interfaces (APIs) for local area network software. Software such as SNA 3270 emulation packages an d Lotus Notes op er ate on to p of the Ne tBIOS laye r. Microsoft LAN Manager uses NetBIOS extensively for identifying clients and servers.

NetBIOS is based on 16-character named “services” that connect to each other. Servers advertise their implementation of a named service, and clients try to find servers by transmitting broadcast frames that contain the name of the service they want.

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Forcing a Local Domain With NetBIOS Name Filters

Wildcard Name Patterns

Another Use of Name Filters

The NetBIOS Name Filtering feature can also force a local domain, or context, of a NetBIOS name. All branch offices, for example, may connect to an SNA gateway function in OS/2 by accessing a gateway local to the branch. Under normal bridging conditions, you configure the SNA gateway NetBIOS server with a different name for each branch office and every workstation to attach to the name for its branch office.

With NetBIOS Name Filters, you can block the local service name (for example,

“SNA_GW”) on the WAN link so that NetBIOS broadcasts to and from that name are not forwarded across to the internetwork.This feature lets the branches use the same name for their loc al SNA ser vi ce a nd you can configure all th e workstations to access the same local SNA name.

Name filter patterns may contai n “wildca rd” char acte rs such as “?” that mat ches any character or “*” at the end of the pattern that matches all remaining characters. As a result, a single filter record can pass or block a large set of NetBIOS names. Unlike current MAC Filter and Protocol filters for a bridge, a packet may match more than one filter record.

For this reason, NetBIOS Name Caching operates using an ordered list of name matching records. A pa cket is compared again st ea ch name matching str ing i n or der, and the action for the first match is taken. If a packet does not match any N etBIOS Name Filter record, the Default NetBIOS Filter Action is taken.

Another way of using NetBIOS Name Filters is to pass all NetBIOS broadcasts except those that are identified in the NetBIOS Name Filter table. This can be used, for example, to restrict access to a particular server to the local segment.

Checking NetBIOS Broadcasts

The NetBIOS Name Filtering feature does not check every NetBIOS packet. It only checks the NetBIOS broadcast packets that are used to initiate a session. Activating NetBIOS Name Filtering does not affect NetBIOS sessions already in progress.

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Configuring NetBIOS Name Filtering

Introduction This section describes how to use the Control Terminal Port (CTP) to configure

NetBIOS Name Filtering.

How to Configure NetBIOS Name Filtering

Bridge Link Parameters Record

Follow these steps:

Step Action

1 Configure the NetBIOS Name Filter Action parameter in the Bridge Link

Parameters.

2 Configure the parameters in th e NetBIOS Name Filter Table record.

Figure 40 highlights the parameter, NetBIOS Name Filter Action, in the Bridge Link Parameters record .

Node: Address: Date: Time: Menu: Configure Bridge Path

Bridge Parameters Bridge Link Parameters

Entry Number Hop Count Limit Largest Frame Size MAC Address Filter Action Protocol Filter Action

NetBIOS Name Filter Action

STPE Link State

Figure 40. Bridge Link Parameters Record

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Configuring

To access the NetBIOS Name Filter Action parameter, follow the steps below:

NetBIOS Name Filtering

Step Action Result

1 Select Configure -> Configure

Bridge -> Bridge Link Parameters from the CTP Main

menu.

Entry Number 1 appears.

Note

The table has one entry for each logical bridge link in the bridge node. Bridge Link Entry 1 is reserved for the primary LAN interface. The WAN bridge links start at entry 5.

2 Enter the number of the link that

you are defining and complete the NetBIOS Name Filter Action parameter using the description in the Parameters section that follows.

Parameter The NetBIOS Name Filter Action parameter is in the Bridge Link Parameters record.

NetBIOS Name Filter Action

Range: PASS, BLOCK, NONE Default: NONE Description: When using NetBIOS Name Filters, set the NetBIOS Name Filter

Action to BLOCK on Bridge Link 1 (the LAN link). Then define the NetBIOS Name Filter Table records with patterns for each of the server names that you want to access.

• PASS — Passes all frames with a NetBIOS name that is not listed in the NetBIOS Name Fi lter Table.

• BLOCK — Blocks all frames with a NetBIOS name that is not listed in the NetBIOS Name Filter Table.

• NONE — Indicates no NetBIOS name filtering for the link.

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Configure NetBIOS Name Filter Table

Figure 41 highlights the NetBIOS Name Filter Table selection in the Configure Bridge menu.

Node: Address: Date: Time: Menu: Configure Bridge Path: (Main.5.22)

Bridge Parameters Bridge Link Parameters MAC Address Filter Table Protocol Filter Table NetBIOS Name Filter Table LSS Parameters LLC LT Station Table LLC LT WAN Parameters LLC LT Profile Table

#Enter Selection:

Configuring NetBIOS Name Filter Table

Figure 41. Configure Bridge Menu

To configure the NetBIOS Name Filter Table, follow these steps:

Step Action Result

1 Select Configure -> Configure

Bridge ->NetBIOS Name Filter Table. from the CTP Main menu.

The first entry of the NetBIOS Name Filter Table appears.

Note

You can enter up to 255 entries in the table. Each entry can be a wildcard pa ttern that matches a class of servers used in an organization.

2 Complete the reco rd by configuring

the parameters using the description

shown in the “Parameters” section on page 81”.

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Typical Filtering For the typical case, where you filter client broadcast traffic by default and pass

server traffic as discussed in the ““Typical Filtering” section on page 81.”

• Define onl y the NetBIOS Name field.

• Define one record for each wildcard pattern that encompasses all NetBIOS service names.

Parameters These parameters make up th e NetBIOS Name Filter Table record:

String Type

Range: ASCII, Hex Default: ASCII Description: This parameter determines how you enter the 16-character

NetBIOS name for this record . ASCII mea ns tha t you en ter ASCI I characters for the name. The name is left-justified, blank filled to the 15th byte, and the 16th byte is ignored. Hex means that you enter hexa decimal valu es for up to al l 16 bytes. The string is left-justified and the remaining bytes are ignored.

NetBIOS Name

Range: 0 to 16 ASCII cha racters ( if par ameter St ring Type=ASCII). Blank

set to null.

2 to 32 hexadecimal digits (if parameter String Type=hex) Default: <blank> Description: This name string is matched against Net BIOS packets. ASCII-type

strings are case-sensitive. They may contain the wildcard

character “?” that matches any character, or “*” as the last

character that matches all remaining characters. Hex type strings

may contain the sequence “**” for a byte position to indicate a

wildcard match of any byte value.

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Incoming NetBIOS Name Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: The following describes the options that you can define for the

link:

• PASS — Passes all incoming frames with a specified NetBIOS name on all links.

• BLOCK — Blocks all incoming frames with a specified NetBIOS name on all links. Passes incoming frames with other NetBIOS names on all links.

• PASSLIST — If you choose this value, you need to specify a pass list in the List of Links parameter. Links that are listed pass the frame. Links that are not listed block the frame. An empty list means that all links block frames.

• BLOCKLIST — If you choose thi s valu e, you nee d to s pecif y a block list in t he Li st of Links parame ter. Links that are liste d block the frame. Links that are not listed pass the frame. An empty list means that all links pass frames.

Note

If you chose PASS or BLOCK, skip the List of Links parameter.

Incoming NetBIOS Name List of Links

Range: 1, 5 to 36 Default: The individual numbers correspond to the links that you filter

according to the preceding parameter.

Description: The following describes the options that you can define for the

link:

• PASSLIST — Passes all incoming frames on the l inks that are listed. Blocks all th e in coming frames on the l inks t hat ar e not listed. An empty list means that all links block the frames.

• BLOCKLIST — Blocks all incoming fr ames on the links that are listed. Passes all the incoming frames on the links that are not listed. An empty list means that all links pass the frames. You can enter a range of link numbers, for example, 1, 6, 8-12 indicates 1, 6, 8, 9, 10, 11, and 12.

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Outgoing NetBIOS Name Link Action

Range: PASS, BLOCK, PASSLIST, BLOCKLIST Default: PASS Description: These are the options that you can define for the link

•PASS

— Passes outgoing frames with the specified NetBIOS name on all links. All outgoing frames with other NetBIOS names are blocked on all links.

• BLOCK — Blocks outgoing frames with the specified NetBIOS name on all links. All outgoing frames with other NetBIOS names are passed on all links.

• PASSLIST — Passes all outgoing frames on th e links tha t you listed in the List of Links parameter. Blocks all the outgoing frames on the links that are not listed. An empty list means that all links block the frames.

• BLOCKLIST — Blocks all outgoing frames on the links that you listed in the List of Links parameter. Passes all the outgoing frames on the links that are not listed. An empty list means that all links pass the frames.

Note

If you chose PASS or BLOCK, skip the List of Links parameter.

Bridge Filtering

Outgoing NetBIOS Name: List of LInks

Range: 1, 5 to 36 Default: The individual numbers correspond to the links that you filter

according to the preceding parameter.

Description: The following describes the options that you can define for the

link:

• PASSLIST — Passes all outgoing frames on the li nks that are listed. Blocks all the outgoing frames on the links that are not listed. An empty list means that all links block the frames.

• BLOCKLIST — Blocks all outgoing frames on the listed links. Passes all the outgoing frames on the links that are not listed. An empty list means that all links pass the frames.

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NetBIOS Name Filtering Statistics

Introduction For each bridge link, you can display the number of packets discarded due to

matching a Ne tBIOS name filter on a bridge filter statistics screen. There are separate counts for the number discarded on incoming and outgoing directions for each bridge link.

Check Detailed Bridge Link Stats

Figure 42 shows the detailed statistics screen that includes counts of the number of NetBIOS broadcasts filtered on the link.

Node: Address: Date: Time: Detailed Bridge Link Statistics: Bridge Link 01 Page: 2 of 2

Filter Discards: In Out RIF Error Discards:

Source MAC Address: 0 0 Segment Mismatch: 0 Dest MAC Address: 0 0 Duplicate Segment: 0 Protocol Filtered: 0 0 NETBIOS Filtered: 46 0 Hop Count Exceeded: 0

Total Filter Discards: 46 0

Press any key to continue ( ESC to exit ) ...

Figure 42. Detailed Bridge Link Statistics

For More Details... Refer to t he “Detailed Bridge Link Statistics” section on page 127.

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NetBIOS Packet Formats

Introduction NetBIOS Name Filtering operates only on the Microsoft or IBM-compatible

NetBIOS implementations, which represents the majority of NetBIOS implementations. It does not recognize at this time Novell’s implementation of NetBIOS over IPX, nor does it recognize the packet format of NetBIOS over TCP (RFC 1000).

NetBIOS Name Filtering operates on Ethernet LANs.

IBM NetBIOS Formats

When to Use NetBIOS Name Filtering

IBM NetBIOS formats are documented in the IBM publicat ion LAN Technical Report for IEEE 802.2 and NetBIOS Interfaces, SC-303587.

Configure NetBIOS Name Filtering when:

All of the following are true:

• The bridged packet is a MAC-level multicast or broadcast, that is, the first transmitte d bit of the destination is set.

• The bridged packet contains an 802.2 LLC field (that is, on Ethernet implementation, the pack et does not use an Ethe rType code to distinguish the packet form at).

• The LLC DSAP/SSAP/CTL fields are:

0xF0 0xF0 x03

The first byte follo wing the ab ove LLC l ayer i s cons idere d of fse t 0 of the NetBIO S PDU (protocol data unit).

• The two bytes at NetBIOS offset 2-3 are 0xFF and 0xFE (NetBIOS frame delimiter).

Either one of the following is true:

• The NetBIOS command byte at offset 4 is:

00 (Add_Group_Name) or 01 (Add_Name Query)

The packet field to be compared to the NetBIOS Name Filter list is the SOURCE name field, occupying the 16 bytes starting an offset 0x1C in the NetBIOS PDU.

• The NetBIOS command byte at offset 4 is:

08 (Datagram) or 0x0A (Name Query)

The packet field to be compared to the NetBIOS Name Filter list is the DESTINATION name field, occupying the 16 bytes starting at offset 0x0C of the NetBIOS PDU.

When Filters Are Applied

NetBIOS na me filters are applied to the broadcast packets that are transmitted in order to initiate NetBIOS sessions and to broadcast datagrams. Application of NetBIOS filters does not halt the operation of any NetBIOS sessions already in progress.

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Spanning T ree Protocol Entity (STPE)

Introduction The Spanning Tree Protocol Entity (STPE) is part of the PathBuilder S200 series

switch Source Route Bridge functionality. The parameters that control Spanning Tree Protocol operation are in the Bridge Record and Bridge Link Record. In the Bridge Record, the STPE Control parameter setting determines whether Automatic or Manual Spanning Tree is used.

For detailed inf ormation a bout the paramete rs in t he Bridge Record and in the Bridge

Link Record, refer to the “Bridge Parameters” and “Bridg e Link Paramete rs” sections earlier in this guide.

Automatic Spanning T ree

Manual Spanning Tree

What You Need to Configure

Automatic Spanning Tree is dynamic and involves more parameters that enable and control the Spanning Tree Protocol messages that communicate betwee n the bridge s. By processing these messages, the bridges automatically determine a spanning tree for the network. These messages are continually updated so the spanning tree automatically adjusts to the current topology. These messages consume a small amount of the bandwidth. The automatic version is redundant since PathBuilder S200 series switch has the capability of re-autocalling the destination, thereby rerouting over another link.

Manual Spanning Tree is static and cannot adjust to bridge network topology changes. However, the process is more straightforward and does not consume network bandwidth (no Hello frames are used). The Spanning Tree is manually configured on a bridge link basis using the Bridge Link “STPE Link State” parameter (FORWARD/BLOCK).

When you configure a node fo r bri dging op erati on, the spanni ng tr ee par ameter s that appear on the Bridge Paramet ers Record an d Bridge Link Recor d depend on whethe r you configure manual or automatic spanning tree.

Configuration

STPE Control= AUTO STPE Control = MANUAL

Bridge Record STPE Control = Auto

Bridge Priority Max Age Hello Time Forward Delay

Bridge Link Record

STPE Priority STPE Path Cost

STPE Control = Manual Bad Hello Threshold Bad Hello Count

STPE Link State

Note

All bridges in a network must operate in the same mode, either all automatic or all manual.

Custom Software Key

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One Custom Software Key (CSK) enables both the Source Route Bridging and the Spanning Tree Protocol Entity.

Spanning Tree Protocol Entity (STPE)

Bridge Links There are three types of bridge links within a given spanning tree network:

• The Root Bridge Link. The link representing the best path to the root bridge. A root link is always on the spanning tree.

• The Designated Bridge Links. All the other bridge links on the spanning tree.

• The Standby Bridge Links. All other bridge links which are not on the spanning tree.

All the bridge links of the root bridge are in the spanning tree and are designated bridge links.

Forwarding and Blocking States

Topology Change Notification

After the sp anning tree is determined, all root links and all designated link s are placed in a forwarding state and standby links are placed in a blocking state. These states refer to the action that a link performs on data fra mes. For Source Route Bridging, forwarding and blocking refer to Spanning Tree Explorer data frames (Specifically Routed Frames and All Route Explorer frames are not subjected to blocking/forwarding by this link state).

When a link is in blocking state, it still monitors and passes to its own bridge the Hello message from the adjacen t designat ed bridge link. Bri dge links ar e not put into a forwarding state immediately upon determining their link classification. Forwarding Delay is u sed to allow the determination of the spa nni ng t ree network to stabilize. This pre vents the net work from se nding infor mation f rames into te mporary routing loops.

The Topology Change Notification Bridged Packet Data Unit (BPDU) is used by a bridge that notices a topology change to send a notification in the direction of the Root Bridge. This occurs only during Automatic spanning tree operation.

When the Root Bridge finally gets this notification, it sets the topology change notification bit in the BPDU that it periodically generates. This informs all bridges that there has been a change in topology and that they should expect that station locations might have changed.

In a manual spanning tree, all the single paths are manually assigned. No Hello frames are exchanged between bridges; rather, each bridge port in the network is configured to either forward or block all Spanning Tree Explorer frames. If a link or bridge goes down, then that path stays broken until the problem is fixed.

No topology change notif ication oc curs in manual spannin g tree opera tion. You have to adjust the spanning tree to changes in your network either by reconfiguring the spanning tree or wait until the lost path is restored.

A manual spanning tree forms fixed single route paths between LANs, and cannot dynamically reestablish an alternate path for the broken one. However, the PathBuilder S200 series switch LAN option can use its SVC rerouting capability to overcome this problem. The PathBuilder S200 series switch senses the break, drops the original SVC between the bridged nodes, and re-autocalls creating another SVC connection using a different path across the WAN.

Since a manual spanning tree does not send Hello messages between bridges, it minimizes network bandwidth overhead. An automatic spanning tree requires sending and receiving BPDUs, whi ch consumes proces sing cycles from th e CPU of a node and therefore increases CPU use. A manual spanning tree avoids this usage.

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Tips on Spanning Tree

Determining a spanning tree in order to set up a man ual tree may seem more labor intensive t han letting th e bridge netw ork determine the tree by algorithm. However, even with automatic spanning tree determination, you must study the possible arrangements of resulting trees and assign the bridge priorities accordingly to avoid unreasonable performance due to long data paths.

In fact, this responsi bi li ty po ints out a major disadvanta ge of usi ng a bri dge ne twork in a mesh topology instea d of a ro uter. The spanning tree protocol does not allo w the bridges to determi ne optimal paths and to route frames along them. Try ing to handle this task manually by configuring bridges and bridge links quickly becomes unwieldy as soon as additional loops are possible and one tries to maintain optimal traffic routing when faced with a variety of possible link or bridge failures.

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STPE Parameter Setting Considerations

Introduction This section discusses how the bridge and bridge link parameters can be used to

influence the design of a bridge network and to show how they relate to overall PathBuilder S200 series switch configuration during spanning tree operation.

Note

You should thoroughly understand the spanning tree protocol and how its parameters influence performance before you consider changing SPTE-related these parameters in a PathBuilder S200 series switch network. Otherwise, because of the critical nature of the timers involved, the spanning tree topology may become unstable. It may become dif f icult t o tra ce thi s beha vio r as the ef fect might occur only occasionally and only in certain types of traffic patterns.

Example of a Bridge Network With Spanning Tree

Figure 43 shows a bridge network composed of si x PathBuil der S200 ser ies swit ches and five LANs. The links that are in the blocking stat e have been selected to achieve the shortest path for the bulk of the expected data flow.

Bridge 1 MAC Address:

0F-00-3E-00-10-50 08-00-3E-00-10-60

LAN 1

LAN 3

Bridge 1

Bridge 3

Bridge 2

Bridge 4

LAN 2

08-00-3E-00-20-4008-00-3E-00-20-30

LAN 4

Bridge 5

08-00-3E-00-30-10 08-00-3E-00-30-20

LAN 5

Bridge 6

Figure 43. Example of a Bridge Network

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Setting the Root Bridge of the Spanning T ree

The bridge with the lowest Bridge ID becomes the root bridge in a spanning tree network.

The Bridge ID is made up of two parts: the Bridge Priority and the MAC address of the LAN port. You modify these elements during bridge configuration from the Bridge Priority parameter in the Bridge Parameters record and the MAC Address parameter in the LAN Port record.

All bridges have the same default pri or it y value (32768). So, wit hout any changes to this value, the MAC address of the LAN port determines the root bridge in a network.

If you want to control which bridge becomes the root bridge, modify the Bridge Priority value appropr iat el y.

For example:

Bridge ID: equals (Bridge Priority Value in hex) + (MAC Address)

The default bridge priority value is 32768 (8000 in hex). So, a bridge with a MAC address of 08-00-3E-02-53-8F and a default bridge priority value would have this bridge ID:

80-00 08-00-3E-02-53-8F

Bridge Priority

MAC Address

Determining Root Links and Designated Links

Figure 44. Example of Bridge ID and MAC Address

A Root Link is the Bridge Link on a particul ar bri dge that is the pre ferred pat h to the Root Bridge.

A Designated Link is all other links that are part of the spanning tree. In Automatic mode, the Root Link is determined by summing path costs from a

bridge to the Root Bridge. Path costs are configured in the Bridge Link Record. If there are multiple pa ths to t he Root Brid ge, th e bridg e selec ts the ro ute with the least cost to the root as the preferred link (Root Link).

All other links associated with the bridge become Designated Links. For example, in the network in Figure 43, bridge 3 receives messages from bridges

1, 4, and 5 because these bridges are adjacent (directly connected by links). If the cost of traversing an y of the WAN links is equal and bridges 1, 4, and 5 are re porti ng B1 as the root and that the y know how to g et to i t, then bridge 3 will ch oose li nk 6 as the preferred link to the root because this path will have the least cost to the root.

Note

The fewest number of links involved yields the lowest cost—the fact that the link is directly attached to the root bridge is coincidental in this example.

The path cost to the root bridge has an influence on the spanning tree topology. The bridge link parameter called STPE Pa th Cost is the pa rameter that sets the incremental path cost to the root, should that bridge link be followed to the root bridge. In general, the speed of the bridge link is the most important factor that determines the path cost increment.

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Determining Path Costs

Bridges use Path Cost to determine their Root Link. The range of Path Cost is 0 to

65535. The lower the path c ost, th e mor e likely t his pa th wi ll be use d. Use Thi s tabl e to determine the path costs for each type of link in your network.

Type of Network Speed STPE Path Cost

802.3 10 Mbps 10

802.5 4 Mbps 25

802.5 16 Mbps 6 serial 1.54 Mbps 65 serial 384 kbps 260 serial 56 kbps 1768 serial 19.2 kbps 3536

For speeds not listed, interpolate to reasonable values. The valid range for path cost is 0 to 65535 so that when values are determined, they should not be such that the total path cost along any reasonable route adds up to more than 65535.

Some bridge manufacture rs may list a dif fer ent set of value s fo r path co st incr emen t. It is important that the same rule be applied to all bridges involved in the spanning tree calculation.

Returning to the mesh network in Figure 43, look at bridge B3: if the WAN lines are all 19.2 kbps and the links are directly connected with a single SVC hop, then their incremental cost fo r WAN links can be set to STPE Pat h Cos t = 353 6. Therefore, B3 will see messages from oth er bridge links resulting in the following co st to the root bridge:

• From bridge 1 link 6: root is bridge 1, cost to root = 3536

• From bridge 4 link 8: root is bridge 1, cost to root = 7072 (3536+3536)

• From bridge 5 link 9: root is bridge 1, cost to root = 14154 (3536+10+3536+3536+3536)

Based on these numbers, B3 determines B1 to be the root bridge, because B1’s bridge ID is lower than all reported root bridges (including B3’s own bridge ID). B3 also designates bridge link 6 as the root link since it has the least cost to the root.

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Consider the Nature and Expected Number of SVCs

A further consideration for setting path cost is the nature and expected number of SVCs that the bridge link uses to achieve its connectivity and adjust the value of incremental path cost accordingly. For example, consider the topology shown in Figure 45.

Node B Node A

Bridge 1

X25-1

X25-3

X25-2

MX25

Bridge 2

Node C

Bridge 3

Node D Node E

Bridge 4

Figure 45. Bridge Links Within Network

Bridge 2 is linked to bridge 1 by two separate links. The link through Node B must traverse two separate SVC hops while the direct link has only a single hop. If the speed of the lines are all equal, then the cost for the bridge link through Node B should be higher than the cost for the direct link.

On the other hand , if the amou nt of traf f ic ( due t o sour ces ot her than br idgin g tra f fic) causes added delay for the direct route, or if the direct route has a lower speed, it might be better to use the direct route as a backup. Therefore one would set the cost for the direct route higher than for the Node B route. For the multipoint line connecting bridges 2, 3, and 4, the cost for each link should be increased in proportion to the amount of bandwidth-sharing involved. This also accounts for the fact that a slave node such as Node D or Node E must wait t o be pol led before it can pass data to its master, thus adding some extra delay.

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Other Considerations for Selecting Links

There are two f ina l considerations when selecting links on the basis of reported cost, when the costs and indicated root bridge on different links are the same. The first is the case where, for example, B4 receives a message on link 8 from B3 designating B1 as the root bridge with a cost of 10608 to the root. At the same time, B4 receives a message on link 8 from B2 designating B1 as the root bridge with a cost of 7072. In this case, B4 will select link 7 as th e root l ink beca use the span ning tr ee algo ri thm dictates that if more than one message has the same root bridg e indicated, at th e same cost to the root, then the message with the higher priority-reporting adjacent should be given priority. In this case, B2 has been configured to have a higher priority (lower Bridge ID) than B3, so B4 selects link 7 as its root link.

The second consideration occurs when two links on the same bridge are receiving messages from the same adjacent bridge, and the messages report the same root bridge and the same cost to the root bridge. This could occur if there were two links between B3 and B4. The bridge will choose the link with the lower bridge link priority. The priority for the link is a 2-byte number formed by concatenating the value of the parameter STPE Priority with the link number.

LAN 3

Bridge 3

Bridge 4

LAN 4

Figure 46. Two Bridge Links Between B3 and B4

For example, B3 sends messages t o B4 that the root bridge is B1, and that the cost to the root is 10608 (3536+3536). To cause bridge 4 to favor link 11 over link 8, configure:

link 8: STPE Priority = 128 (80 hex) link 11: STPE Priority = 64 (40 hex)

In this example, should a link between bridge 3 and bridge 4 be necessary for a spanning tree, bridge 4 will favor link 11 and remove link 8 from the tree.

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The same priority mechanisms that determine the root link are also applied in determining which links become designated links (a root link is never a designated link). The designated link is the link that is respo nsible for issuing the bridge messages when more than one link is involved in a network. For example, in the network in Figure 43, Bridge 5 and bridge 6 are connected to LAN 5 and will both issue each other spanning tree messages until they determine which one of them is the designated bridge for LAN 5. Once determined, the designated bridge issues bridge messages and the other bridge only listens (unless it has received another message from another link that would make its link the designated bridge; such a message must have higher priority than the one it receives from its designated adjacent). Another case where there is contention and resolution to a designated bridge is link 8 between bridge 3 and bridge 4.

T o de term ine whi ch lin k becomes design ated, t he same set of prior ity p aramete rs ar e used as in determining the root link. In this case, the designated link is the link issuing the message that:

• Identifies the root br idge with the lowest numerical bridge ID

• Has the lowest cost to the root (assuming there is a tie in reporting the root bridge)

• Identifies itself with a h igher priority ID (assuming there is a tie in reporting the root bridge and the cost to the root bridge)

• Has the higher priority link (assuming all of the above are tied)

In this network, bridge 5 link 1 is the designated link for LAN 5 because between bridge 5 link 1 and bridge 6 link 1, bridge 5 link 1 generates a message with a lower cost to the roo t tha n brid ge 6 lin k 1 (t hey both h ave th e s ame roo t). Bet ween brid ge 3 and bridge 4 on link 8, bridge 3 link 8 becomes the designated link because it has a lower cost to the link.

Links that are not root links or are not designated links are not part of the spanning tree. Links that ar e not on the spanni ng tr ee do not fo rward d ata packe ts (o r span ning tree explorer frames in source route bridging). However, they are constantly receiving bridg e messa ges on th ese l inks f ro m the d esi gnate d brid ges an d c omparing these messages to those they originate. This action allows the bridge to detect failures and adjust the spanning tree, should this become necessary.

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Spanning T ree T imers

Introduction If the spanning tree converges to a final topology (it usually does, but

misconfiguration as discussed below can cause instability and lack of convergence), the topology is maintained by timed messages initiated by the root bridge and sent out its designated li nks. Subsequently, bridges receive the message on the ir root li nk and in turn pass the message along the spanning tree by transmitting it on their designated links.

Timer Parameter s The root bridge messa ge has ti mer pa ramete r valu es tha t all br idges should cop y and

use. These timers are:

• Message Age

• Max Age (Bridge Parameters Record)

• Hello Time (Bridge Parameters Record)

• Forward Delay (Bridge Parameters Record)

Notice that the last three are parameters configured for each bridge. Once the root bridge is determined, however, all the other bridges use the value in the root bridge initiated message rather than their own configured values. The Max Age and Hello Time are the two principal timers used by the spanning tree protocol for detecting a fault condition.

When selecting values to configure these two parameters, consider the fact that the bridge network is, when X.25 WAN circuits are used, overlaid onto an underlying network which has its own timers and recovery procedures. It is important that the two networks do not interfere with each other’s protocols, especially where timer considerations are involved.

Hello Timer Hello messages are sent by the Roo t Bridge at speci fic time inte rvals . These i nterva ls

are determined by the Hello Timer parameter configured in the Bridge Parameters record.

If the bridges in the network receive these Hello messages, then this indicates to the bridges that the Root Bridge is functioning and the path from the bridge to the Root Bridge is fun ctional as well.

If a bridge does not receive a Hello message from the Root Bridge within the time allowed by the Max Age Timer parameter, then that bridge begins the process of recalculating the spanning tree for the network.

Max Age The Max Age is a configurable parameter on the Bridge Parameters Record. This

parameter indicates to a bridge when to discard information about the Root Bridge and the link to the Root Bridge.

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Other Considerations

One important consideration is based on the fact that any bridge downstream from the root bridge copies the message received on the root link (which is also passed along designated links), and the retained copy is constantly aged. If the age of the message reaches the value of Max Age, the bridge discards the stored message and chooses another l ink as th e root li nk. Pot entiall y this co uld resul t in a di f ferent bridge selected as the root bridge and in turn cause it to recalculate the root, root link, and designated links (recalculate the spanning tree). Since the root port generates the update message every Hello Time period (in seconds), it is obvious that the parameter Max Age should not have a value less than or in fact near the value of Hello Time. The spanning tree protocol (IEEE 802.1D) dictates that a bridge should enforce the following relationship:

Max Age >= 2 x (Hello Time - 1)

In the PathBuilder S200 series switch this rule is not strictly enforce d by CTP configuration checks. You should check that the values are satisfactory for the operational environment. The Max Age range of values is 6 to 40 and the default is

20. The Hello Time range of values is 1 to 4 and the default is 2 seconds. These values allow the enforcement of timer relationships for any reasonab le choi ce of values. The factor of two between Max Age and Hello Time allows one of the hello messages to be lost due to, for example, congestion.

In general, increa sing the va lue of Max Age less ens the chan ce of a fal se timeout d ue to a delay of the hello message. When bridge traffic must compete with other traffic on WAN links, setting this value can become an important consideration. On the other hand, beyond a certain point, a large value for Max Age may cause the detection of a true fault to be prolonged beyond what is desired. The Hello Time should be considered similarly:

• Too low a value causes frequent transmission of the message, resulting in network overhead.

• Too long an interval between transmissions forces a longer Max Age which results in lack of responsiveness to failure situations.

In spite of the overhead, a short Hello Time helps in cases where the message might be inadvertently lost in the network (not likely) or where a short convergence time for the spanning tree is desired.

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EXP Computer PathBuilder S200 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Restricted Rights Notification for U.S. Government Users

Proprietary Material

Bridging Features and Capabilities

Ethernet LAN

Mixed LAN Bridging

MAC Addressing

LLC2 Local Termination

Autolearn for Local T ermination

Filtering

Spanning T ree Protocol

Dual Ethernet LANs

Basic Remote Bridging Examples

Bridge Hardware Components in PathBuilder S200 Series Switches

Setting Up WAN Operation for Bridging

Configuring the PathBuilder S200 Series Switch for Bridging Operation

Bridge Parameters

Bridge Link Parameters

LAN Connection Table

Limiting Bridge Frame Sizes

Configuring Translational Bridging

Bridge Frame Handling

Configuring Source Route Bridging Operation

Connecting a Station to a Server in Source Ro ute Bridging

Transparent Bridging for Ethernet LANs

Forwarder Database and Spanning Tree

Using Filters

T ransparent Bridge Co nfiguration Parameters

Bridge Filtering

MAC Address Filtering

MAC Address Filtering Examples

Identifying Address Links for MAC A ddressing

MAC Wildcard Filtering

Configuring the MAC Address Filter Table

Protocol Filtering

Configuring the Protoco l Filter Table

NetBIOS Name Filtering

Configuring NetBIOS Name Filtering

NetBIOS Name Filtering Statistics

NetBIOS Packet Formats

Spanning Tree Protocol Entity (STPE)

STPE Parameter Setting Considerations

Spanning T ree T imers