MSTP question

[chris99099]

Hi,

Can anyone help me please? I'm designing a network which has two 5400 as core routers, the edge routers are 2650's. On the core I have MSTP configured. I configured two instances like this:
spanning-tree
spanning-tree config-name "XXXXX"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1 2 4 10 12 20 30 50
spanning-tree instance 1 priority 1
spanning-tree instance 2 vlan 6-9 11 13 21 31 51
spanning-tree instance 2 priority 2

On the other 5400 switch, I configured it the same but priority instance 1 =2 and instance 2=1.

My question is, what is the best way to configure the edge switches? Do I have to configure MSTP on them as well? They have two uplinks, one to each core 5400 switch.
Could someone please give me an example what that config should look like?

[Matt Hobbs]

On your edge switches, you can simply set the basic MSTP settings that you've used on the core (no need to set the priority, leave them at the default of 8)

e.g.

spanning-tree
spanning-tree config-name "XXXXX"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1 2 4 10 12 20 30 50
spanning-tree instance 2 vlan 6-9 11 13 21 31 51

[chris99099]

Thanks for your answer, another question is: on the edge-switches I configured only some of the vlan's. So when I insert the instances the switch says he can't find the vlan's. Is it a problem when I configure the instances with only the vlan's the switch knows about, or do I need to configure all vlan's also on the edge-switches?

[Matt Hobbs · Accepted solution]

You should configure each switch's spanning-tree settings so that they have all VLAN's matching the core switches (even if no ports are untagged members on the edge switch).

You should also tag all switch to switch links to be members of all VLANs. The reason that you should do this is that in the event of a fail-over, a valid path for all VLANs can be found. If you do not do this you may find that some VLANs have connectivity whereas others don't.

Also make sure you update the switches to the latest version firmware, there has been some changes to MSTP recently that makes it a bit easier. Previously with the older firmware you also needed to set the edge-port status for your client ports, this is no longer necessary with the latest firmware.