Cabletron Systems SmartSwitch Adjusting Spanning-Tree Parameters, Setting the Bridge Priority

Chapter 3: Bridging Configuration Guide

The SSR supports per VLAN spanning tree. By default, all the VLANs defined belong to the default spanning tree. You can create a separate instance of spanning tree using the following command:

Create spanning tree for a VLAN.

pvst create spanningtree vlan-name

<string>

By default, spanning tree is disabled on the SSR. To enable spanning tree on the SSR, you perform the following tasks on the ports where you want spanning tree enabled..

Enable spanning tree on one or	stp enable port <port-list>
more ports for default spanning
tree.
Enable spanning tree on one or	pvst enable port <port-list>spanning-tree
more ports for a particular VLAN.	<string>

Adjusting Spanning-Tree Parameters

You may need to adjust certain spanning-tree parameters if the default values are not suitable for your bridge configuration. Parameters affecting the entire spanning tree are configured with variations of the bridge global configuration command. Interface-specific parameters are configured with variations of the bridge-group interface configuration command.

You can adjust spanning-tree parameters by performing any of the tasks in the following sections:

•Set the Bridge Priority

•Set an Interface Priority

Note: Only network administrators with a good understanding of how bridges and the

Spanning-Tree Protocol work should make adjustments to spanning-tree parameters. Poorly chosen adjustments to these parameters can have a negative impact on performance. A good source on bridging is the IEEE 802.1d specification.

Setting the Bridge Priority

You can globally configure the priority of an individual bridge when two bridges tie for position as the root bridge, or you can configure the likelihood that a bridge will be selected as the root bridge. The lower the bridge's priority, the more likely the bridge will be selected as the root bridge. This priority is determined by default; however, you can change it.

62 SmartSwitch Router User Reference Manual