Cisco Systems BC-23 Tuning the Transparently Bridged Network

Configuring Transparent Bridging

Tuning the Transparently Bridged Network

BC-60

Cisco IOS Bridging and IBM Networking Configuration Guide

Note The VLAN Configuration WebTool hypertext link is listed in the router’s home page only

when a PA-12E/2FE port adapter is installed in the router.

Tuning the Transparently Bridged Network

The following sections describe how to configure features that enhance network performance by

reducing the number of packets that traverse the backbone network:

•Configuring Circuit Groups

•Configuring Constrained Multicast Flooding

In the process of loop elimination, the spanning-tree algorithm always blocks all but one of a group of

parallel network segments between two bridges. When those segments are of limited bandwidth, it might

be preferable to augment the aggregate bandwidth between two bridges by forwarding across multiple

parallel network segments. Circuit groups can be used to group multiple parallel network segments

between two bridges to distribute the load while still maintaining a loop-free spanning tree.

Deterministic load distribution distributes traffic between two bridges across multiple parallel network

segments grouped together into a single circuit group. As long as one port of the circuit group is in the

forwarding state, all ports in that circuit group will participate in load distribution regardless of their

spanning-tree port states. This process guarantees that the computed spanning tree is still adaptive to any

topology change and the load is distributed among the multiple segments. Deterministic load distribution

guarantees packet ordering between source-destination pairs, and always forwards traffic for a

source-destination pair on the same segment in a circuit group for a given circuit-group configuration.

Note You should configure all parallel network segments between two bridges into a single

circuit group. Deterministic load distribution across a circuit group adjusts dynamically to

the addition or deletion of network segments, and to interface state changes.

If a circuit-group port goes down and up as a result of configuration or a line protocol change, the

spanning-tree algorithm will bypass port transition and will time out necessary timers to force the

eligible circuit-group ports to enter the forwarding state. This avoids the long disruption time caused by

spanning-tree topology recomputation and therefore resumes the load distribution as quickly as possible.

To tune the transparently bridged network, perform the following tasks:

1. Define a circuit group.

2. Optionally, configure a transmission pause interval.

3. Modify the load distribution strategy.