Blade ICE G8000 Spanning Tree Group configuration guidelines, Changing the Spanning Tree mode

RackSwitch G8000 Application Guide

Port Priority

The port priority helps determine which bridge port becomes the root/designated port.

The case for the root port is when 2 switches are connected using a minimum of two links with the same path-cost. The case for the designated port is in a network topology that has multiple bridge ports with the same path-cost connected to a single segment—the port with the lowest port priority becomes the designated port for the segment. Use the following command to configure the spanning-tree port priority (Interface Port mode):

RS G8000 (config-if)# spanning-tree stp 1 priority <0-240, in steps of 16>

Port Path Cost

The port path cost assigns lower values to high-bandwidth ports, such as 10 Gigabit Ethernet, to encourage their use. The objective is to use the fastest links so that the route with the lowest cost is chosen. A value of 0 indicates that the default cost will be computed for an auto-negoti- ated link speed.

Use the following command to modify the port path cost:

RS G8000 (config-if)#spanning-tree stp 1 path-cost <0-200000000>

Spanning Tree Group configuration guidelines

This section provides important information on configuring Spanning Tree Groups (STGs):

Changing the Spanning Tree mode

When the spanning-tree mode is changed (for example, RSTP to MSTP),

„You must reconfigure spanning-tree parameters for each STG, including VLAN assign- ment.

„If a STG in RSTP mode is disabled and then re-enabled, the STP topology does not converge rapidly.

76 „ Chapter 5: Spanning Tree BMD00041, November 2008