MSTP short for Multiple Spanning Tree Protocol is an IEEE
standard was inspired by Cisco Multiple Instances Spanning Tree
Protocol. In MSTP, you can create a multiple groups for different types
of VLANs and then run single instance of spanning tree for a single
group of VLANs. But in traditional PVST, there is a different instance
of spanning tree for each VLAN. Single instance for a group of VLANs
reduce the number of BPDUs, root bridges and root ports in the network.
You can perform a proper load balancing across redundant links using
MSTP group instances.
Today tip will help you to configure Multiple
Spanning Tree Protocol for different VLANS using three switches. In this
case, we will try to configure three different switches with two MSTP
instances.
Follow the network topology of three switches to manage the group of
VLANS in given figure:
MSTP configuration on Switch-A
In global configuration mode
SWITCH-A(config)#vlan 10-30
SWITCH-A(config-vlan)#exit
SWITCH-A(config)#vtp domain Marketing
SWITCH-A(config)#spanning-tree mode mst
SWITCH-A(config)#spanning-tree mst configuration
SWITCH-A(config-mst)#name morning
SWITCH-A(config-mst)#revision 10
SWITCH-A(config-mst)#instance 1 vlan 10-20
SWITCH-A(config-mst)#instance
2 vlan 21-30
SWITCH-A(config-mst)#exit
SWITCH-A(config)#spanning-tree mst 1 root primary
SWITCH-A(config)#spanning-tree mst 2 root secondary
SWITCH-A(config)#exit
MSTP configuration on Switch-B
In global configuration mode
SWITCH-B(config)#spanning-tree mode mst
SWITCH-B(config)#spanning-tree mst configuration
SWITCH-B(config-mst)#name morning
SWITCH-B(config-mst)#revision 10
SWITCH-B(config-mst)#instance 1 vlan 10-20
SWITCH-B(config-mst)#instance 2 vlan 21-30
SWITCH-B(config-mst)#exit
SWITCH-B(config)#spanning-tree mst 2 root primary
SWITCH-B(config)#spanning-tree mst 1 root secondary
SWITCH-B(config)#exit
MSTP configuration on Switch-C
In global configuration mode
SWITCH-C(config)#spanning-tree mode mst
SWITCH-C(config)#spanning-tree mst configuration
SWITCH-C(config-mst)#name morning
SWITCH-C(config-mst)#revision 10
SWITCH-C(config-mst)#instance 1 vlan 10-20
SWITCH-C(config-mst)#instance 2 vlan 21-30
SWITCH-C(config-mst)#exit
Now verify the MSTP status on switch
SWITCH-C for instance
1 and 2,
run the command
SWITCH-C#
show
spanning-tree mst 1
MST1 vlans mapped: 10-20
Bridge address 001a.a181.1880
priority 32769 (32768 sysid 1)
Root address 000c.85d7.d780 priority
24577 (24576 sysid 1)
port Fa0/2
cost 200000
rem hops 19
Interface Role Sts Cost
Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------
Fa0/1
Altn BLK 200000 128.3 P2p
Pre-STD-Rx
Fa0/2
Root FWD 200000 128.4 P2p
Pre-STD-Rx
SWITCH-C#
show
spanning-tree mst 2
MST2 vlans mapped: 21-30
Bridge address
001a.a181.1880 priority 32770 (32768
sysid 2)
Root address
000c.85de.1100 priority 24578 (24576
sysid 2)
port Fa0/1
cost 200000
rem hops 19
Interface Role Sts Cost
Prio.Nbr Type
---------------- ---- --- --------- -------- -----------------------
Fa0/1
Root FWD 200000 128.3 P2p Pre-STD-Rx
Fa0/2
Altn BLK 200000 128.4 P2p
Pre-STD-Rx
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