Concept Guide

protocol spanning-tree mstp
no disable
MSTI 1 VLAN 100
MSTI 2 VLAN 200-300
All bridges in the MSTP region must have the same VLAN-to-instance mapping.
To view which instance a VLAN is mapped to, use the show spanning-tree mst vlan command from EXEC Privilege
mode.
DellEMC(conf-mstp)#name my-mstp-region
DellEMC(conf-mstp)#exit
DellEMC(conf)#do show spanning-tree mst config
MST region name: my-mstp-region
Revision: 0
MSTI VID
1 100
2 200-300
To view the forwarding/discarding state of the ports participating in an MSTI, use the show spanning-tree msti
command from EXEC Privilege mode.
DellEMC#show spanning-tree msti 1
MSTI 1 VLANs mapped 100
Root Identifier has priority 32768, Address 0001.e806.953e
Root Bridge hello time 2, max age 20, forward delay 15, max hops 19
Bridge Identifier has priority 32768, Address 0001.e80d.b6d6
Configured hello time 2, max age 20, forward delay 15, max hops 20
Current root has priority 32768, Address 0001.e806.953e
Number of topology changes 2, last change occured 1d2h ago on Te 1/21
Port 374 (TenGigabitEthernet 1/21) is root Forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.374
Designated root has priority 32768, address 0001.e806.953e
Designated bridge has priority 32768, address 0001.e806.953e
Designated port id is 128.374, designated path cost 20000
Number of transitions to forwarding state 1
BPDU (MRecords): sent 93671, received 46843
The port is not in the Edge port mode
Port 384 (TenGigabitEthernet 1/31) is alternate Discarding
Port path cost 20000, Port priority 128, Port Identifier 128.384
Designated root has priority 32768, address 0001.e806.953e
Designated bridge has priority 32768, address 0001.e809.c24a
Designated port id is 128.384, designated path cost 20000
Number of transitions to forwarding state 1
BPDU (MRecords): sent 39291, received 7547
The port is not in the Edge port mode
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.
Multiple Spanning Tree Protocol (MSTP)
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