Reference Guide

Multiple Spanning Tree Protocol (MSTP) | 591
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 27-1 by default yields the same forwarding path for both MSTIs.
Figure 27-5, 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 27-5.
Figure 27-5. 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.
For a bridge to be in the same MSTP region as another, all three of these qualities must match exactly. The
default values for name and revision will match on all Dell Force10 FTOS equipment. If you have
non-FTOS equipment that will participate in MSTP, ensure these values to match on all the equipment.
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: 0-61440, in increments of 4096
Default: 32768
msti instance bridge-priority
priority
PROTOCOL MSTP
Note: Some non-FTOS equipment may implement a non-null default region name. SFTOS, for example,
uses the Bridge ID, while others may use a MAC address.
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