Configuring Transparent Bridging
Transparent and SRT Bridging Configuration Task List
BC-29
Cisco IOS Bridging and IBM Networking Configuration Guide
To configure transparent and SRT bridging, you must perform the following tasks:
•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
Assigning a Bridge Group Number and Defining the Spanning-Tree Protocol
The first step in setting up your transparent bridging network is to define a Spanning-Tree Protocol and
assign a bridge group number. You can choose either the IEEE 802.1D Spanning-Tree Protocol, the
earlier DEC protocol upon which this IEEE standard is based or VLAN bridge Spanning Tree Protocol.
Cisco expanded the original 802.1 D Spanning-Tree Protocol in Cisco IOS Release 12.1 by providing
VLAN bridge Spanning-Tree Protocol support and increased port identification capability. Furthermore,
the enhancement provides:
•More than one byte on a port number to distinguish interfaces
•An improved way to form the port ID
Port Number size of the Port ID support is applied only to IEEE and VLAN-bridge Spanning-Tree
Protocols. The DEC protocol only has 8 bits on the Port ID, so the extension of the Port ID cannot be
applied.
The expansion of the Port Number field into the port priority portion of the Port ID changes the useful
values the port priority can be assigned.
The way to calculate the Port Path Cost is only supported in IEEE and VLAN-bridge Spanning-Tree
Protocol environment.
To assign a bridge group number and define a Spanning-Tree Protocol, use the following command in
global configuration mode:
The IEEE 802.1D Spanning-Tree Protocol is the preferred way of running the bridge. Use the DEC
Spanning-Tree Protocol only for backward compatibility. The VLAN-bridge Spanning-Tree Protocol,
introduced in Cisco IOS Release 12.1, supports the following media: Ethernet, fast Ethernet, FDDI,
ATM and serial (HDLC, PPP, Frame Relay IETF, SMDS, x25).
Assigning Each Network Interface to a Bridge Group
A bridge group is an internal organization of network interfaces on a router. Bridge groups cannot be
used outside the router on which it is defined to identify traffic switched within the bridge group. Bridge
groups within the same router function as distinct bridges; that is, bridged traffic and bridge protocol
data units (BPDUs cannot be exchanged between different bridge groups on a router. Furthermore,
bridge groups cannot be used to multiplex or de-multiplex different streams of bridged traffic on a LAN.
An interface can be a member of only one bridge group. Use a bridge group for each separately bridged
(topologically distinct) network connected to the router. Typically, only one such network exists in a
configuration.
Command Purpose
bridge bridge-group protocol {ieee | dec |
vlan-bridge}
Assigns a bridge group number and defines a Spanning-Tree Protocol
as IEEE 802.1D standard, DEC or VLAN bridge.