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RSTP to MST transition - config and some questions

Maurice David Wörnhard
Occasional Contributor

RSTP to MST transition - config and some questions

Hi all

(I also cross-posted to the old forums at https://forums13.itrc.hp.com/service/forums/categoryhome.do?categoryId=269)

Over the weekend I transitioned from RSTP to MST in our pretty simple network, but I wonder if I have done it right.

I am using one 3500yl and 5 3400cl. The topology:

Network Topology

All switches are in the same region and have the same mst configuration digest.

(all switches)# spanning-tree instance 1 vlan 1 2
(all switches)# spanning-tree instance 2 vlan 3 4

In order to have some load-balancing between the two fiber trunks MST was set up like this:

sw-1 and sw-3:
# spanning-tree instance 1 trk1 path-cost 6667
# spanning-tree instance 1 priority 2
# spanning-tree instance 2 trk1 path-cost 20000
# spanning-tree instance 2 priority 4

sw-2 and sw-4:
# spanning-tree instance 1 trk1 path-cost 20000
# spanning-tree instance 1 priority 4
# spanning-tree instance 2 trk1 path-cost 6667
# spanning-tree instance 2 priority 2

No special modifications on sw-5 and sw-6.

I also would like sw-3 or sw-4 to be both regional and IST roots, so I increase their priority:

sw-3# spanning-tree priority 0
sw-4# spanning-tree priority 1

Does this look correct? The network works as expected so far, and

show spanning-tree root-history ...

indicates that the correct switches are roots.

Some questions:
- What does "spanning-tree <some-trunk> path-cost/priority nnn" do when using MST? Are these values just used for CST?
- Any suggestions on how to check that the VLAN-load-balancing actually works as expected?

Best
Maurice

2 REPLIES
Maurice David Wörnhard
Occasional Contributor

Re: RSTP to MST transition - config and some questions

Michael Breuer gave a good answer on the IT Resource center forums - see https://forums13.itrc.hp.com/service/forums/questionanswer.do?threadId=1453386
Helper
Valued Contributor

Re: RSTP to MST transition - config and some questions

hi,

 

To complete the reply already mention : https://forums11.itrc.hp.com/service/forums/questionanswer.do?admit=109447626+1288171369708+28353475&threadId=1453386

 

To verify spanning-tree vlan load-balancing, you need to verify your path (forwarding/blocking ports) to check if the tree is as expected.

"show spanning-tree instance <IST or instance-id> "

 

I don't remember if PCM+ offer a topology map with vlan or instance active by links. You can try it

 

Bye,