Reference Guide

Influencing MSTP Root Selection
MSTP determines the root bridge, but you can assign one bridge a lower priority to increase the probability that it
becomes the root bridge.
To change the bridge priority, use the following command.
• Assign a number as the bridge priority.
PROTOCOL MSTP mode
msti instance bridge-priority priority
A lower number increases the probability that the bridge becomes the root bridge.
The range is from 0 to 61440, in increments of 4096.
The default is 32768.
By default, the simple configuration shown previously yields the same forwarding path for both MSTIs. The following
example shows how R3 is assigned bridge priority 0 for MSTI 2, which elects a different root bridge than MSTI 2.
To view the bridge priority, use the show config command from PROTOCOL MSTP mode.
Example of Assigning and Verifying the Root Bridge Priority
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
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 2-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 match on all Dell Networking FTOS equipment. If you have non-FTOS equipment that
participates in MSTP, ensure these values match on all the equipment.
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.
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