Spanning Tree oddness and advice

[Tony Barrett_2]

Ok, another spanning tree question!

We have a 5406 at the core, which feeds to 6 other 5406's via 10G fibre. The 'other' 5406's feed edge switches, which in turn have edge clients connected.

We have MST spanning tree running on all 5406's and edge switches  (except the core - I didn't think there was the requirement here) which prevents standard network loops. This is working ok.

I need to setup some spanning tree redundancy, and intend to do this between all 5406's (not core). We have multiple VLAN's running over the 10G links, and the redundant paths will be 1gig.

All other 5406's have 'spanning-tree priority 0' set. All I planned to do was set the path-cost for the 1G redundant link to 5000 (10G path cost is 'auto' and 2000) and let spanning-tree do it's thing, but when I connect everything up - the redundant 1G paths just stay 'disabled'. I expected them to come 'up' then go into a blocked state.

MST talks about setting up instances, so I'd set the primary instance to be the 10G path, and the secondary instance to be the 1G path, but I don't know why the redundant paths didn't come up at all, and could do with some advice on how to set this up to ensure that in the event of primary path failure, all VLAN's are sent over the redundant path.

Hope that makes sense, but I'm happy to elaborate if necessary.

[Richard Brodie_1]

All other 5406's have 'spanning-tree priority 0' set.

That is a rather odd thing to do: 0 is the highest priority. It means that one of the switches with 0 priority will be root.

All I planned to do was set the path-cost for the 1G redundant link to 5000 (10G path cost is 'auto' and 2000) and let spanning-tree do it's thing

That sounds reasonable enough, although my question would be 'what problem is that solving that you would have with the default values?'

when I connect everything up - the redundant 1G paths just stay 'disabled'. I expected them to come 'up' then go into a blocked state.

Me too; that suggests something else is going on. Do you have link lights on these ports? Have you got any special configuration on these ports, like say bpdu-guard?

MST talks about setting up instances.

Life is too short to mess around with multiple spanning tree instances. in 90% of cases. It needs quite a bit of careful design and  manual configuration to gain any benefit.