Cisco Systems BC-23 - page 9

Configuring Transparent Bridging

Transparent and SRT Bridging Configuration Task List

BC-31

Cisco IOS Bridging and IBM Networking Configuration Guide

The primary application of transparently bridged VLANs constructed in this way is to separate traffic

between bridge groups of local network interfaces, to multiplex bridged traffic from several bridge

groups on a shared interface (LAN or HDLC serial), and to form VLANs composed of collections of

bridge groups on several routers. These VLANs improve performance because they reduce the

propagation of locally bridged traffic, and they improve security benefits because they completely

separate traffic.

In Figure 9, different bridge groups on different routers are configured into three VLANs that span the

bridged network. Each bridge group consists of conventionally bridged local interfaces and a

subinterface on the backbone FDDI LAN. Bridged traffic on the subinterface is encapsulated and

“colored” with a VLAN identifier known as a security association identifier common to all bridge

groups participating in the VLAN. In addition, bridges only accept packets bearing security association

identifiers for which they have a configured subinterface. Thus, a bridge group is configured to

participate in a VLAN if it contains a subinterface configured with the VLAN’s characteristic security

association identifier. See the “Complex Integrated Routing and Bridging Example” section on page66

for an example configuration of the topology shown in Figure9.

Note The 802.10 encapsulation used to “color” transparently bridged packets on subinterfaces

might increase the size of a packet so that it exceeds the MTU size of the LAN from which

the packet originated. To avoid MTU violations on the shared network, the originating

LANs must either have a smaller native MTU than the shared network (as is the case from

Ethernet to FDDI), or the MTU on all packet sources on the originating LAN must be

configured to be at least 16 bytes less than the MTU of the shared network.

Figure 9 Transparently Bridged VLANs on an FDDI Backbone

Bridge

group 18

"Striped"

packets

Bridge

group 54

"Dot"

packets

Bridge

group 3

"Sliced"

packets

Bridge

group 7

"Sliced"

packets

Bridge

group 8

"Dot"

packets

Bridge

group 1

"Sliced"

packets

Bridge

group 6

"Striped"

packets

Router 1 Router 2

Router 3

Shared network

"Striped"

packets

"Dot"

packets

"Sliced"

packets

S3228

Contents

Main Configuring Transparent Bridging Technology Overview Transparent and SRT Bridging Transparent Bridging Features Integrated Routing and Bridging Bridge-Group Virtual Interface Page Other Considerations SRT Bridging Features Transparent and SRT Bridging Configuration Task List Configuring Transparent Bridging and SRT Bridging Assigning a Bridge Group Number and Defining the Spanning-Tree Protocol Assigning Each Network Interface to a Bridge Group Choosing the OUI for Ethernet Type II Frames Transparently Bridged VLANs for ISL Page Routing between ISL VLANs Page Configuring a Subscriber Bridge Group Configuring Transparent Bridging over WANs Configuring Fast-Switched Transparent Bridging over ATM Configuring Transparent Bridging over DDR Configuring Transparent Bridging over Frame Relay Configuring Transparent Bridging over Multiprotocol LAPB Configuring Transparent Bridging over SMDS Configuring Transparent Bridging over X.25 Configuring Concurrent Routing and Bridging Configuring Integrated Routing and Bridging Assigning a Bridge Group Number and Defining the Spanning-Tree Protocol Configuring Interfaces Enabling Integrated Routing and Bridging Configuring the Bridge-Group Virtual Interface Configuring Protocols for Routing or Bridging Configuring Transparent Bridging Options Disabling IP Routing Enabling Autonomous Bridging Configuring LAT Compression Establishing Multiple Spanning-Tree Domains Preventing the Forwarding of Dynamically Determined Stations Forwarding Multicast Addresses Configuring Bridge Table Aging Time Filtering Transparently Bridged Packets Setting Filters at the MAC Layer Filtering by Specific MAC Address Page Page Page Filtering LAT Service Announcements Specifying Deny or Permit Conditions for LAT Group Codes on Output Adjusting Spanning-Tree Parameters Setting the Bridge Priority Setting an Interface Priority Assigning Path Costs Adjusting BPDU Intervals Disabling the Spanning Tree on an Interface Configuring Transparent and IRB Bridging on a PA-12E/2FE Ethernet Switch Configuring the PA-12E/2FE Port Adapter Monitoring and Maintaining the PA-12E/2FE Port Adapter Configuring Bridge Groups Using the 12E/2FE VLAN Configuration WebTool Page Tuning the Transparently Bridged Network Configuring Circuit Groups Configuring Constrained Multicast Flooding Monitoring and Maintaining the Transparent Bridge Network Transparent and SRT Bridging Configuration Examples Basic Bridging Example BC-64 The configuration file for the router in Figure 12 is as follows: Concurrent Routing and Bridging Example BC-65 Basic Integrated Routing and Bridging Example Figure 13 Basic IP Routing using Integrated Routing and Bridging The following example shows the relevant portions of the configuration for the router in Figure 13: BC-66 Complex Integrated Routing and Bridging Example Figure 14 Complex Integrated Routing and Bridging Example The following example shows the relevant portions of the configuration for the router: BC-67 Integrated Routing and Bridging with Multiple Bridge Groups Example Figure 15 Integrated Routing and Bridging with Multiple Bridge Groups The following example shows the relevant portions of the configuration for the router in Figure 15: Transparently Bridged VLANs Configuration Example BC-68 Router One Router Two BC-69 Router Three BC-70 Routing between VLANs Configuration Example Ethernet-to-FDDI Transparent Bridging Example Ethernet Bridging Example SRT Bridging Example BC-73 Configuration for the New York City Router Configuration for the Thule, Greenland Router Multicast or Broadcast Packets Bridging Example Figure 18 Network Demonstrating Output Address List Filtering BC-74 The correct access list would be as follows: X.25 Transparent Bridging Example Figure 19 X.25 Bridging Examples Following are the configuration commands for each of the bridges depicted in Figure19: X.25 Bridge 2 Bridge 1 Bridge 3 BC-75 Frame Relay Transparent Bridging Examples Figure 20 illustrates three bridges connected to each other through a Frame Relay network. Figure 20 Frame Relay Bridging Example Bridging in a Frame Relay Network with No Multicasts Bridge 2 Bridge 1 Bridge 3 Transparent Bridging over Multiprotocol LAPB Example BC-77 Fast-Switched Transparent Bridging over ATM Example (Cisco 7000) The following configuration example enables fast-switched transparent bridging over ATM: Transparent Bridging over DDR Examples Fast-Switched Transparent Bridging over SMDS Example Complex Transparent Bridging Network Topology Example Page Page Page BC-82 Fast Ethernet Subscriber Port, Frame Relay Trunk Example ATM Subscriber Ports, ATM Trunk Example The following example uses ATM subinterfaces as the subscriber ports and the ATM as the trunk: BC-83 Configuration of Transparent Bridging for PA-12E/2FE Port Adapter Example BC-84 Configuration of IRB for PA-12E/2FE Port Adapter Example