Avaya Bridging User Manual

Configuring Bridging Services

Router Software Version 10.0

Site Manager Software Version 4.0

Part No. 112950 Rev. A

January 1996

4401 Great America Parkway 8 Federal Street Santa Clara, CA 95054 Billerica, MA 01821

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(continued)

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About This Guide

If you are responsible for conﬁguring and managing Bay Networks routers, you should read this guide to learn how to customize Bay Networks router software for bridging services.

This guide,

• Transparent bridging services (Chapter 1)

• Source routing bridge services (Chapter 2)

• NetBIOS services (Chapter 3)

• Translation bridge services (Chapter 4)

• Native mode LAN (NML) services (Chapter 5)

Audience

Written for system and network managers, this guide presents information on how to conﬁgure the Bay Networks implementation of bridging interfaces to suit your environment.

Before Y ou Begin

Before using this guide, you must complete the following procedures:

• Create and save a conﬁguration ﬁle that has at least one bridging interface.

• Retrieve the conﬁguration ﬁle in local, remote, or dynamic mode.

Conﬁguring Bridging Services

, offers details on conﬁguring

• Reboot the router with the conﬁguration ﬁle. Refer to

Conﬁguring Routers

for instructions.

xvii

Configuring Bridging Services

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CompuServe

xviii

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About This Guide

(44) 272-760681.

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xix

Configuring Bridging Services

Conventions

This section describes the conventions used in this guide. angle brackets (< >) Indicate that you choose the text to enter based on the

arrow character (➔) Separates menu and option names in instructions.

description inside the brackets. Do not type the brackets when entering the command. Example: if command syntax is

192.32.10.12

Example: Protocols

<ip_address>

➔

AppleTalk identiﬁes the

, you enter

ping

AppleTalk option in the Protocols menu.

ping

bold text

Indicates text that you need to enter and command

dinfo

names in text. Example: Use the

command.

brackets ([ ]) Indicate optional elements. You can choose none, one,

or all of the options.

italic text

Indicates variable values in command syntax descriptions, new terms, ﬁle and directory names, and book titles.

quotation marks (“ ”) Indicate the title of a chapter or section within a book.

screen text

ellipsis points Horizontal (. . .) and vertical ellipsis points indicate

Indicates data that appears on the screen. Example:

Bay Networks Trap Monitor Filters

()

Set

omitted information.

vertical line (|) Indicates that you enter only one of the parts of the

command. The vertical line separates choices. Do not type the vertical line when entering the command.

Example: If the command syntax is

show at routes show at routes

nets

, you enter either

show at nets

, but not both.

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Acronyms

APE all-paths explorer frame ARE all-routes explorer frame ARP Address Resolution Protocol BPDU Bridge Protocol Data Unit CUGID closed user group ID DA destination address DLCI data link connection identiﬁer DLSw data link switching DSAP destination service access point FCS frame check sequence FDDI Fiber Distributed Data Interface IEEE Institute of Electrical and Electronic Engineers IP Internet Protocol IPX Internet Packet Exchange LLC logical link control LNM LAN Network Manager MAC media access control MIB Management Information Base MTU Maximum Transmission Unit NetBIOS Network Basic Input/Output System NML Native Mode LAN OUI organizationally unique identiﬁer

About This Guide

xxi

Configuring Bridging Services

PPP Point-to-Point Protocol RFC Request for Comments RIF Routing Information Field SA source address SAP service access point SMDS Switched Multimegabit Data Services SNAP Subnetwork Access Protocol SR source routing SRF speciﬁcally routed frame SSAP session service access point STE spanning tree explorer frame TB transparent bridging XNS Xerox Network System

xxii

Using Transparent Bridge Services

This chapter contains information on the following topics:

• The transparent bridge, including an overview of the transparent bridge and details on how the spanning tree algorithm works

• Enabling bridge service and spanning tree on an interface

• Transparent bridge parameters, including information on how to edit the parameters using Conﬁguration Manager.

• Deleting the bridge and spanning tree from the router

Transparent Bridge Overview

Chapter 1

Transparent bridges are data-link layer relay devices that connect two or more networks. They use media access control (MA C) source and destination addresses to relay frames between connected networks.

Note:

We use the terms

throughout this chapter.

The transparent bridge provides three primary services:

• Learns the addresses of endstations on connected networks

• Forwards or drops frames based on knowledge it acquires about endstation addresses or user-conﬁgured ﬁlters

• Ensures a loop-free topology throughout the extended network, using the spanning tree algorithm

bridge

and

transparent bridge

interchangeably

1-1

Configuring Bridging Services

A transparent bridge also provides some translation services, converting frames for bridging between Ethernet/802.3 LANs and Fiber Distributed Data Interface (FDDI) LANs. Refer to “The Translation Process” later in this chapter for details on translation services.

How the Bridge Works

The bridge receives and examines every frame transmitted on the networks to which it is attached. It learns endstation addresses by reading the source address of the endstation that transmitted the frame and noting which LAN interface received the frame. The bridge enters this information into a data structure called

forwarding table

the For example, in Figure 1-1, if Node 2 transmits a frame onto the network for the

ﬁrst time, the bridge receives the frame and makes an update to its forwarding table. The bridge notes that Node 2 is in the direction of LAN A.

, which the bridge constantly updates.

Forwarding Table

Node MAC Addr LAN

1-2

00:00:A2:00:00:01 00:00:A2:00:00:02

00:00:A2:00:00:03 00:00:A2:00:00:04

LAN A

Bridge

Node 1

MAC Address=

00:00:A2:00:00:01

Node 2

MAC Address=

00:00:A2:00:00:02 00:00:A2:00:00:03

Figure 1-1. Forwarding Table Update

A A

B B

MAC Address=

Update

Node 3

LAN B

Node 4

MAC Address=

00:00:A2:00:00:04

Using Transparent Bridge Services

The bridge then forwards (relays to another network) or drops (discards) the frame based on the forwarding table entries. When the bridge receives a frame, it compares the frame’s destination address with addresses in the forwarding table. One of these situations results:

• If the frame’s destination address is on the same LAN as its source address, the bridge discards the frame; all nodes on that LAN already received this frame.

• If the frame’s destination address is on a different LAN than its source address, the bridge

forwards

the frame to that LAN.

• If there is no match for the frame’s destination address in the forwarding table, the bridge forwards the frame to all networks except the one that received the frame. This is called ﬂooding.

• If the frame is destined for the bridge (for example, a spanning tree frame), the bridge forwards the frame to the appropriate bridge entity and processes it internally .

Note:

If a frame is forwarded or ﬂooded to a LAN using a different data-link level protocol, the bridge translates the frame to the appr opriate frame format before transmission.

The T ranslation Process

The transparent bridge translates frames for bridging between Ethernet/802.3 LANs and FDDI LANs. When the transparent bridge receives Ethernet/802.3 frames destined for an FDDI LAN, it reformats those frames to the FDDI MAC frame format. The transparent bridge sets the original MAC frame type in the logical link control (LLC) header. Therefore, if the frame passes through a second, FDDI-to-Ethernet/802.3 bridge, that bridge can translate the frame back to its original format.

The bridge translates all Ethernet MAC frames to FDDI MAC and IEEE 802.2 LLC/Subnetwork Access Protocol (SNAP) encapsulation, as speciﬁed by RFC

1042. Protocols that adhere to RFC 1042 include DECnet Phase IV, Novell, AppleTalk Phase I and II, Xerox Network System (XNS), Internet Package Exchange (IPX), and Internet Protocol (IP).

Figure 1-2 shows the format and values of the LLC and SNAP headers of these frames after translation.

1-3

Configuring Bridging Services

DSAP SSAP Control OUI Protocol Type

0 xAA 0 xAA 03 000000 (OriginalType)

Figure 1-2. RFC 1042 Encapsulation

AppleTalk Address Resolution Protocol (ARP) frames (Ethernet frames with a protocol type equal to 80F3) require special translation by the Bridge Tunnel Service.

Figure 1-3 illustrates the LLC and SNAP headers of the AppleT alk ARP outbound frame after the Bridge Tunnel Service translation.

DSAP SSAP Control OUI Protocol Type

0 xAA 0 xAA 03 0000F8 80F3

SNAP LLC

1-4

Key

SNAP = Subnetwork Access Protocol LLC = logical link control DSAP = destination service access point SSAP = session service access point OUI = organizationally unique identifier

Figure 1-3. Bridge Tunnel Service Encapsulation

The bridge translates all IEEE 802.2 LLC frames by removing the length ﬁeld. Protocols in this category include AppleTalk Phase 2, Novell Proprietary, and IP.

Figures 1-4 and 1-6 illustrate different LAN conﬁgurations and show how Bridge A translates different types of frames originating on LAN 1 for transmission across the FDDI LAN. Figure 1-5 shows how Bridge B translates frames transmitted from the FDDI LAN to LAN 2.

Using Transparent Bridge Services

Ethernet LAN1 Ethernet LAN2

Bridge A

Bridge B

FDDI LAN

Ethernet to FDDI Translation

Through Bridge A to FDDI LANFrom Ethernet LAN

DA DA SASA

TYPE

=80F3

DATA FCS

SNAP LLC OUI

AA AA 03 00 00 00

Bridge A

• Extracts addressing information from the Ethernet header.

• Incorporates address information into newly generated FDDI MAC header.

• Encapsulates Ethernet data according to RFC 1042.

• Recalculates frame check sequence (FCS).

Ethernet (AppleTalk ARP) to FDDI Translation

From Ethernet LAN

DA SA

TYPE =80F3

DATA FCS

Through Bridge A to FDDI LAN

DA SA

SNAP LLC OUI

AA AA 03 00 00 F8

TYPE

=80F3

TYPE

=80F3

DATA

FCSDATA

FCS

Bridge A

• Extracts addressing information from the Ethernet header.

• Incorporates address information into newly generated FDDI MAC header.

• Encapsulates Ethernet data within an IEEE 802.2H-defined SNAP header that has an organizationally unique identifier (OUI) of 0000F8.

• Recalculates FCS.

Figure 1-4. Ethernet to FDDI Translation

1-5

Configuring Bridging Services

Ethernet LAN1 Ethernet LAN2

Bridge A

Bridge B

FDDI LAN

FDDI to Ethernet Translation

From FDDI LAN

DA SA

SNAP LLC OUI

AA AA 03 00 00 00 =80F3

TYPE

FCSDATA

Through Bridge B to Ethernet LAN

Bridge B

• Extracts addressing information from the FDDI header.

• Incorporates address information into newly generated Ethernet MAC header.

• Removes RFC 1042 from Ethernet data.

• Recalculates frame check sequence (FCS).

FDDI to Ethernet (AppleTalk ARP) Translation

From FDDI LAN

DA SA

SNAP LLC OUI

AA AA 03 00 00 F8

TYPE

=80F3

DATA

FCS

Through Bridge B to Ethernet LAN

DA SA

TYPE =80F3

DATA FCS

Bridge B

• Extracts addressing information from the FDDI header.

• Incorporates address information into newly generated Ethernet MAC header.

• Removes Ethernet data from an IEEE 802.2H-defined SNAP header that has an organizationally unique identifier (OUI) of 0000F8.

• Recalculates FCS.

Figure 1-5. FDDI to Ethernet Translation

1-6

Using Transparent Bridge Services

Ethernet LAN1 Ethernet LAN2

Bridge A Bridge B

FDDI LAN

802.3 to FDDI Translation

Through Bridge A to FDDI LANFrom 802.3 LAN

DA SA LEN DSAP SSAP CTL DATA FCS DA SA DSAP SSAP CTL DATA FCS

Bridge A

• Extracts addressing information from the 802.3 header.

• Incorporates address information into newly generated FDDI MAC header with no length (LEN) field.

• Encapsulates 802.3 data within FDDI frame.

• Recalculates FCS.

Figure 1-6. Ethernet/802.3 to FDDI Translation

The translation process from the FDDI LAN to Ethernet/802.3 LAN (the process Bridge B performs in Figures 1-5 and 1-6) is a mirror image of the translation process occurring on Bridge A, with one exception: the bridge translates an AppleTalk ARP frame that originates on the FDDI LAN and is destined for an Ethernet/802.3 LAN as shown in Figure 1-7.

1-7

Configuring Bridging Services

AppleTalk ARP frame originating on FDDI LAN

DA SA

SNAP LLC OUI

AA AA 03 = 00 00 00

Through Bridge B to 802.3 LAN

DA SA

SNAP LLC OUI

LEN

AA AA 03 = 00 00 00

Bridge B

• Extracts addressing information from the FDDI MAC header

• Incorporates address information into newly generated 802.3 header

• Adds a length field

• Encapsulates FDDI data according to RFC 1042

• Recalculates FCS

Figure 1-7. AppleTalk ARP (Originating on FDDI) to 802.3 Translation

Spanning T ree Algorithm

TYPE

=80F3

TYPE

=80F3

DATA

FCS

DATA FCS

1-8

The spanning tree algorithm ensures the existence of a loop-free topology in networks that contain parallel bridges. (Refer to

Standard 802.1d Media Access Contr ol (MAC) Bridges

Source Routing Appendix to IEEE

for details on the spanning tree algorithm.) A loop occurs when there are alternate routes between hosts. If there is a loop in an extended network, bridges may forward trafﬁc indeﬁnitely, which can result in increased trafﬁc and degradation in network performance.

Figure 1-8 shows an example of a network containing a loop: two parallel bridges, Bridge 1 and Bridge 2, connect LANs A and B.

IF 9

BR 4

Using Transparent Bridge Services

LAN C

ES K

IF 5

ES J

IF 2

BR 2BR 1

IF 3

IF 6

LAN B

IF 1

IF 8

LAN A

Figure 1-8. Parallel Bridge Topology

When Endstation J initially sends a frame to Endstation K, both Bridge 1 and Bridge 2 read the frame. Since this is the ﬁrst frame sent between J and K, there is no forwarding table entry for J or K on either of the bridges. Each bridge updates its forwarding table to indicate that Endstation J is in the direction of LAN A. Then, each bridge ﬂoods the frame: Bridge 1 forwards the frame over Interface 1 and Bridge 2 forwards the frame over Interface 2. Bridge 2 also forwards the frame over Interface 3; however, to simplify the example, we do not trace this frame.

LAN D

Key

IF = Interface BR = Bridge

ES = Endstation

IF 7

IF 4

BR 3

1-9

Configuring Bridging Services

Next, Endstation K receives tw o copies of the frame, resulting in an inefﬁcient use of the available bandwidth. More serious, however, is the effect of duplicate frames on the two bridges. The frame ﬂooded by Bridge 1 onto Interface 1 is ultimately read by Bridge 2 on Interface 2. When Bridge 2 reads this frame, it updates its forwarding table to indicate that Endstation J is in the direction of LAN B. Similarly, Bridge 1 reads the frame ﬂooded by Bridge 2 and updates its forwarding table to show that Endstation J is in the direction of LAN B. Consequently , the forwarding tables of both bridges are no w corrupted and neither bridge can properly forward a frame to Endstation J.

You can avoid this problem by implementing the spanning tree algorithm, which produces a logical tree topology out of any arrangement of bridges. The result is that a single path exists between any two endstations on an extended netw ork. The spanning tree algorithm also provides a high degree of fault tolerance. It allows the network to automatically reconﬁgure the spanning tree topology if there is a bridge or data-path failure.

The spanning tree algorithm requires ﬁve values to derive the spanning tree topology. The ﬁrst, a multicast address specifying all bridges on the extended network, is media-dependent and is automatically determined by the software. You assign the remaining four values, which are

1-10

• Network-unique identiﬁer for each bridge on the extended network

• Unique identiﬁer for each bridge/LAN interface (called a port)

• Priority specifying the relative priority of each port

• Cost for each port After you assign these values, bridges multicast and process the formatted frames

(called Bridge Protocol Data Units, or BPDUs) to derive a single loop-free topology throughout the extended network. The bridges exchange BPDU frames quickly, minimizing the time that service is unavailable between hosts.

In constructing a loop-free topology, the bridges within the extended network follow these steps:

Elect a root bridge.

The bridge with the lowest priority value becomes the root bridge and serves as the root of the loop-free topology. If priority values are equal, the bridge with the lowest bridge MAC address becomes the root bridge.

IF 3

Bridge A

Using Transparent Bridge Services

Determine path costs.

The path cost is the cost of the path to the root bridge offered by each bridge port.

Select a root port and elect a designated bridge on each LAN.

Each bridge designates the port that offers the lowest-cost path to the root bridge as the root port. In the event of equal path costs, the bridge examines the paths’ interfaces to the root bridge. The port (interface) of the path with the lowest interface priority to the root bridge becomes the root port. For example, Figure 1-9 shows how Bridge A determines its root port.

Given:

Root Bridge

IF 1

IF 2

LAN A

LAN B

IF 4

Path costs from IF 3 to root bridge and from IF 4 to root bridge are equal.

---------AND-------IF 1 = priority 1

IF 2 = priority 2 IF 3 = priority 3 IF 4 = priority 4

Then:

IF 3 becomes root port because IF 1’s priority is lower than IF 2’s

priority.

Figure 1-9. Root Port Determination (Equal Path Costs)

If the paths’ interfaces to the root bridge are also equal, then the root port is the port on the bridge with the lowest priority value (Figure 1-10).

1-11

Configuring Bridging Services

Given: Path costs from IF 3 to root bridge and

from IF 4 to root bridge are equal.

---------AND-------IF 1 = priority 1

IF 2 = priority 1 IF 3 = priority 3 IF 4 = priority 2

Then:

IF 4 becomes root port because it has a higher priority than IF 3.

Same priority

IF 3

Bridge A

Root Bridge

IF 1

IF 2

LAN A

LAN B

IF 4

Figure 1-10. Root Port Determination (Equal Path Costs and Root Interface Priorities)

The spanning tree algorithm selects a bridge on each LAN as the designated bridge. The root port of this bridge has the lowest-cost path to the root bridge. All bridges turn off (set to blocking state) all of the lines except for the single line that is the shortest-cost path to the root and any line attached to the LANs for which the bridge serves as a designated bridge.

1-12

Elect a designated port.

The spanning tree algorithm selects the port that connects the designated bridge to the LAN as the designated port. If there is more than one such port, the spanning tree algorithm selects the port with the lowest priority as the designated port. This port, which carries all extended network trafﬁc to and from the LAN, is in the forwarding state.

Thus, the spanning tree algorithm removes all redundant ports (ports providing parallel connections) from service (places in the blocking state). If there is a topological change or a bridge or data-path failure, the algorithm derives a new spanning tree that may move some ports from the blocking to the forwarding state.

For example, in Figure 1-8, if all path costs are equal and Bridge 2 has the lowestbridge priority (followed by Bridge 3, Bridge 4, and Bridge 1), the spanning tree algorithm may block Bridge 1/Interface 8 and Bridge 4/Interface 9 from service.

Figure 1-11 shows the resulting logical topology, which provides a loop-free topology with only a single path between any two hosts.

BR 2

Using Transparent Bridge Services

LAN B LAN A

IF 1

BR 4BR 1

Given: All path costs are equal.

Interface (IF) number denotes its priority.

----And----

BR 2 = priority 1 BR 3 = priority 2

BR 4 = priority 3 BR 1 = priority 4

IF 2 IF 3

IF 5

Then: Bridge 1/Interface 1 is blocked.

Bridge 4/Interface 5 is blocked.

Result: Loop-free topology

is created.

IF 6

LAN D

IF 7

BR 3

IF 8

LAN C

Figure 1-11. Spanning Tree (Loop-Free) Logical Topology

It is very important to conﬁgure the spanning tree parameters correctly. Consider the typical ﬂow of trafﬁc so that the logical topology that results from the spanning tree algorithm is appropriate for the network.

If, in the network shown in Figure 1-8, a majority of trafﬁc originates on LAN A and is destined for LAN D, it is not practical to set the spanning tree parameters as shown in Figure 1-12. This ﬁgure illustrates an inefﬁcient spanning tree topology for this network because the trafﬁc from LAN A must traverse Bridge 1, LAN B, and Bridge 2 to get to LAN D. LAN B is then congested with unnecessary trafﬁc.

1-13

Configuring Bridging Services

BR 4

IF 5 IF 9

LAN B LAN C

BR 1

Given:

All path costs are equal.

Interface (IF) number

denotes its priority.

----And---BR 4 = priority 1

BR 3 = priority 2 BR 2 = priority 3 BR 1 = priority 4

Figure 1-12. Inefﬁcient Spanning Tree Topology

Filtering Frames

IF 1

IF 8

LAN A

IF 2

BR 2

IF 3

LAN D

Then:

Bridge 2/Interface 2 is blocked.

Bridge 3/Interface 7 is blocked.

Result: Inefficient spanning

tree topology is created.

IF 7

BR 3

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You use ﬁlters mainly for security reasons. They enable the bridge to relay or drop a particular frame based on user-selectable ﬁelds within each of the four encapsulation methods supported by the bridge. These encapsulation methods are

• Ethernet

• IEEE 802.2 LLC

• IEEE 802.2 LLC with SNAP header

• Novell proprietary

Using Transparent Bridge Services

Refer to ﬁlters and how to conﬁgure them for the bridge.

Conﬁguring Trafﬁc Filters and Protocol Prioritization

Enabling Bridge Service

This section describes how to enable bridge service and, optionally, spanning tree on an interface. It assumes you have read

1. Opened a conﬁguration ﬁle.

2. Speciﬁed router hardware if this is a local mode conﬁguration ﬁle.

3. Selected the link or net module connector on which you are enabling bridge

service, or conﬁgured a WAN circuit if this connector requires one.

Enabling Bridge Service on an Interface

To enable bridge service without spanning tree, select Bridge from the Select Protocols menu and click on OK. The Select Protocols menu appears after you either select a link or net module connector, or ﬁnish conﬁguring a WAN circuit.

When you enable bridge service without spanning tree, you need not specify any conﬁguration information, because Conﬁguration Manager supplies default values for the bridge parameters. The protocol pop-up window for the next enabled protocol appears, or, if only bridge is enabled on this circuit, the Bay Networks Conﬁguration Manager window appears. To edit the default values for the bridge parameters, refer to “Editing Bridge Parameters” for instructions.

Conﬁguring Routers

for details about

and that you have

Enabling Spanning Tree on an Interface

To enable spanning tree on an interface, use the following procedure.

1. From the Select Protocols menu, select the Spanning Tree option that is

directly under the Bridge option.

Note that the Conﬁguration Manager also selects the Bridge option because this Spanning Tree protocol cannot run without Bridge enabled.

2. Click on OK.

The Spanning Tree Autoconﬁguration window appears (Figure 1-13).

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Configuring Bridging Services

When you enable spanning tree service, you need only conﬁgure the Bridge Priority and Bridge MAC Address parameters. The Conﬁguration Manager supplies default values for the remaining parameters. If you want to edit the default values, see “Editing Bridge Parameters” later in this section.

Note: Because the spanning tree is global (that is, it runs across all Bridge

circuits), the Conﬁguration Manager only displays the Spanning Tree Autoconﬁguration window the ﬁrst time you specify Spanning Tree for the Bridge. If you have previously speciﬁed Spanning Tree for source routing, this window will not appear. To change the parameter settings at a later time, r efer to the “Editing Bridge Parameters” section.

3. Conﬁgure the parameters, using the descriptions that follow as a guide.

4. When you have conﬁgured the required parameters, click on OK.

A pop-up window prompts

Do you want to edit the Spanning Tree Interface Details?

5. Click on Cancel to enable default Spanning Tree service and display the

next protocol-speciﬁc pop-up window, or click on OK to edit the default spanning tree values.

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(Refer to “Editing Bridge Parameters” for instructions.)

Using Transparent Bridge Services

Figure 1-13. Spanning Tree Autoconﬁguration Window

Parameter: Bridge Priority

Default: 128

Range: 0 to 65535

Function: Combined with the Bridge MAC Address parameter, assigns a 64-bit

bridge ID to the router. This parameter supplies the most signiﬁcant 16 bits of the bridge ID, while Bridge MAC Address supplies the remaining (least signiﬁcant) 48 bits.

The spanning tree uses the bridge ID to select the root bridge. In selecting the root bridge, the spanning tree chooses the bridge with the lowest bridge ID number. Thus, the lower the value you set for this parameter, the more likely it is that the router will be selected as the root bridge.

Instructions: Enter a decimal value from 0 to 65535.

MIB Object ID: 1.3.6.1.4.1.18.3.5.1.2.1.5

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Configuring Bridging Services

Parameter: Bridge MAC Address

Default: Defaults to a unique MAC address that the router automatically creates

based on the router’s backplane ID.

Options: Any valid 48-bit MAC-level address

Function: Combined with the Bridge Priority parameter, assigns a 64-bit bridge ID

to the router. Bridge Priority supplies the most signiﬁcant 16 bits of the bridge ID, while this parameter supplies the remaining (least signiﬁcant) 48 bits.

The spanning tree uses the bridge ID to select the root bridge. In selecting the root bridge, the spanning tree chooses the bridge with the lowest bridge ID number. Thus, the lo wer the setting of Bridge Priority, the more likely it is that the router will be selected as the root bridge. In the event of equal Bridge Priority values, the value of this parameter determines the bridge’s priority.

Instructions: Enter a 48-bit MAC address expressed as a 12-digit hexadecimal value.

We recommend that you set this parameter to the MAC address of one of the router’s spanning tree ports, preferably the one with the lowest priority.

MIB Object ID: 1.3.6.1.4.1.18.3.5.1.2.1.5

Editing Bridge Parameters

Once you conﬁgure a circuit to support the bridge and, optionally, the spanning tree algorithm, you use Conﬁguration Manager to edit the bridge and spanning tree parameters.

This section provides information on how to access and edit these parameters.

Note: If you enable the spanning tree algorithm for your network, the

algorithm reconverges if you dynamically change any of the parameters described in the following sections.

You access all bridge parameters from the Conﬁguration Manager window (Figure 1-14). (Refer to Using Site Manager Software guide for details on accessing this window.)

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Using Transparent Bridge Services

Figure 1-14. Conﬁguration Manager Window

For each bridge and spanning tree parameter, this section provides information about default settings, valid parameter options, the parameter function, instructions for setting the parameter, and the Management Information Base (MIB) object ID.

Technician Interface lets you modify parameters by issuing commands that specify the MIB object ID. This process is equivalent to modifying parameters using Site Manager. For more information about using the Technician Interface to access the MIB, refer to Using Technician Interface Software.

Caution: The Technician Interface does not verify that the value you enter for

a parameter is valid. Entering an invalid value can corrupt your conﬁguration.

Editing Bridge Global Parameters

To edit the bridge global parameters:

1. Select Protocols➔Bridge➔Global from the Conﬁguration Manager

window (refer to Figure 1-14).

set and commit

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Configuring Bridging Services

The Edit Bridge Global Parameters window appears (Figure 1-15).

Figure 1-15. Edit Bridge Global Parameters Window

Edit the parameters, using the descriptions in the next section as a guide.

3. Click on OK to save your changes and exit the window.

Site Manager returns you to the Conﬁguration Manager window.

Bridge Global Parameter Descriptions

Use these parameter descriptions as a guide when you conﬁgure the parameters in the Edit Bridge Global Parameters window (refer to Figure 1-15).

Parameter: Enable

Default: Enable

Options: Enable

Function: Enables or disables bridging on the entire router.

Instructions: Set to Disable if you w ant to disable bridging for all circuits on the router.

MIB Object ID: 1.3.6.1.4.1.18.3.5.1.1.1.1.2

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