COMPUTER TIPS

How to configure MSTP on the Cisco multilayer switches?

 

 

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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