MTSP Help

[adurotec_1]

My configuration:

Two 5406zl switches that have routing and vrrp enabled and numerous VLANS. Please see the attached high level diagram.

I have been configuring my network with MSTP in what I believe is called a load-balanced config, where I have two MSTP instances and I assign different vlans to each instance.

To assign the vlans to each instance I have been assigning vlans that have a vrrp master IP that is assigned to the switch1 vlan interface to the first mstp instance and all the vlans that have a vrrp master IP that is assigned to the switch2 vlan interface to the second mstp instance.

Is this a good way of configuring MSTP for my network? What is a "best practice" for creating mstp instances and assigning vlans?

Everything seems to be working fine, but I want to make sure I am not building towards a disaster.

Thanks,
David

[Michael_Breuer]

Hi David,

rule of thumb is to have MST root bridge on the same chassis as the VRRP Master. That will avoid suboptimal paths.
I.e.:
VLAN 1,3,5 are assigned to instance 1
-> switch 1 is MST root bridge for this instance and VRRP master for these VLANs

VLAN 2,4,6 are assigned to instance 2
-> switch 2 is MST root bridge for this instance and VRRP master for these VLANs.

You have to ensure that crosslink between switch 1 and switch 2 is carrying all VLANs to avoid traffic flow through access switches.

Cheers,

Michael

[adurotec_1]

Michael,

Thanks for the info.

I am a little rusty so bear with me.

As I understand it based on your response, it is preferable to have the MST instance's root bridge on alternating core switches, i.e. instance 1 on switch 1, instance 2 on switch 2.

How do I configure the instances so that this is the end result?

I take it that once I have the MST root bridge designation established, assigning the VLANs to an MST instance would be based on which switch IP is assigned as the vrrp owner in conjunction to which MST instance is on the switch that the vrrp owner resides on?

David

[Michael_Breuer · Accepted solution]

Hi David,

mayb sample config helps you to understand what I mean:

Switch 1:
Root for instance 1, VRRP owner for these VLANs

spanning-tree config-name "CUSTOMER_NAME"
spanning-tree config-revision 1000
spanning-tree instance 1 vlan 1 3 5 7
spanning-tree instance 1 priority 0
spanning-tree instance 2 vlan 2 4 6 8
spanning-tree instance 2 priority 1
spanning-tree bpdu-protection-timeout 300
vlan 1
vrrp vrid 1
owner
virtual-ip-address 1.1.1.254 255.255.0.0
priority 255
enable
exit
exit
vlan 2
vrrp vrid 2
backup
virtual-ip-address 2.2.2.254 255.255.0.0
enable
exit
exit
...
and so on

=========================================
Switch 2
Root for instance 2, VRRP owner for these VLANs

spanning-tree config-name "CUSTOMER_NAME"
spanning-tree config-revision 1000
spanning-tree instance 1 vlan 1 3 5 7
spanning-tree instance 1 priority 1
spanning-tree instance 2 vlan 2 4 6 8
spanning-tree instance 2 priority 0
spanning-tree bpdu-protection-timeout 300
vlan 1
vrrp vrid 1
backup
virtual-ip-address 1.1.1.254 255.255.0.0
enable
exit
exit
vlan 2
vrrp vrid 2
owner
virtual-ip-address 2.2.2.254 255.255.0.0
priority 255
enable
exit
exit
and so on..

Cheers,

Michael

[adurotec_1]

Michael,

Ok, I see what I was missing in my configuration, I was not properly setting the priority of the MST instance on the second switch. I was actually setting the priority for MST instance 1 to priority 0 for both switches and priority 1 for instance 2 on both switches.

Thanks for clarifying that for me.

David