Reference Guide

Multiple Spanning Tree Protocol (MSTP) | 663
Influence MSTP Root Selection
MSTP determines the root bridge, but you can assign one bridge a lower priority to increase the probability
that it will become the root bridge.
To change the bridge priority:
The simple configuration Figure 31-1 by default yields the same forwarding path for both MSTIs.
Figure 31-5, shows how R3 is assigned bridge priority 0 for MSTI 2, which elects a different root bridge
than MSTI 2. View the bridge priority using the command
show config from PROTOCOL MSTP mode,
also shown in Figure 31-5.
Figure 31-5. Changing the Bridge Priority
Interoperate with Non-FTOS Bridges
FTOS supports only one MSTP region. A region is a combination of three unique qualities:
• Name is a mnemonic string you assign to the region. The default region name on FTOS is null.
• Revision is a two-byte number. The default revision number on FTOS is 0.
• VLAN-to-instance mapping is the placement of a VLAN in an MSTI.
Task Command Syntax Command Mode
Assign a number as the bridge priority. A lower number
increases the probability that the bridge becomes the root
bridge.
Range: 0 to 61440, in increments of 4096
Default: 32768
msti instance bridge-priority priority PROTOCOL MSTP
R3(conf-mstp)#msti 2 bridge-priority 0
1d2h51m: %RPM0-P:RP2 %SPANMGR-5-STP_ROOT_CHANGE: MSTP root changed for instance 2. My
Bridge ID: 0:0001.e809.c24a Old Root: 32768:0001.e806.953e New Root: 0:0001.e809.c24a
R3(conf-mstp)#show config
!
protocol spanning-tree mstp
no disable
MSTI 1 VLAN 100
MSTI 2 VLAN 200,300
MSTI 2 bridge-priority 0