CHAPTER
6-1
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
6
Configuring Bridges
This chapter describes how to configure bridging for the ML-Series card. For more information about
the Cisco IOS commands used in this chapter, refer to the Cisco IOS Command Reference publication.
This chapter includes the following major sections:
Understanding Basic Bridging, page 6-1
Configuring Basic Bridging, page 6-2
Monitoring and Verifying Basic Bridging, page 6-3
Transparent Bridging Modes of Operation, page 6-5
Caution Cisco Inter-Switch Link (ISL) and Cisco Dynamic Trunking Protocol (DTP) are not supported by the
ML-Series cards, but the ML-Series broadcast forwards these formats. Using ISL or DTP on connecting
devices is not recommended. Some Cisco devices attempt to use ISL or DTP by default.

Understanding Basic Bridging

The ML-Series card supports transparent bridging for Fast Ethernet, Gigabit Ethernet and POS ports. It
supports a maximum of 255 active bridge groups. For information on the modes of transparent bridging,
see the “Transparent Bridging Modes of Operation” section on page 6-5.
To configure bridging, you must perform the following tasks in the modes indicated:
In global configuration mode:
Enable bridging of IP packets.
Select the type of Spanning Tree Protocol (STP) (optional).
In interface configuration mode:
Determine which interfaces belong to the same bridge group.
The ML-Series card bridges all nonrouted traffic among the network interfaces comprising the
bridge group. If spanning tree is enabled, the interfaces became part o f the same spanning tree.
Interfaces not participating in a bridge group cannot forwa rd bridged traffic.
If the destination address of the packet is known in the bridge table, the packet is forwarded on
a single interface in the bridge group. If the packet’s destination is unknown in the bridge table,
the packet is flooded on all forwarding interfaces in the bridge group. The bridge places source
addresses in the bridge table as it learns them during the process of bridging.