I'm hoping someone can offer me advice or an answer to my problem.
I've been trying to set switch B (A --- B trunked) to be the root bridge for numerous VLANs in my development network.
I'm pretty sure I should accomplish this by ensuring the relevant spanning-tree priority is set low i.e.
interface vlan 3
spanning-tree vlan 3 priority 4096
interface vlan 3
spanning tree vlan 3 priority 8192
however when I change the priority of Switch B the trunk I use to connect via telnet goes down following an error on Switch A of :
SPANTREE-2-PVSTSIM_FAIL: Blocking designated port....
This occurs if I change switch A priority first or not... I've waited a few minutes for the trunk to stop blocking without joy so I'm putting the question here for help.
breifly the setup is
I can connect via console on Switch B and CDP packets are passing between the devices (the trunk native vlan differs from the vlan in question) but not see any of the vlan interface present on Switch A and vice versa.
Thanks in advance
Firstly, is this a mixed-Vendor environment? This sounds similar to an issue I've come across previously with Cisco not playing nice with other spanning-tree devices - Per-VLAN spanning-tree is Cisco Proprietary so other vendors only support STP, RSTP and MST
Second, are you running rapid, or regular Per-Vlan Spanning Tree?
I'd definately recommend setting rapid on both switches by doing a
(config)#spanning-tree mode rapid-pvst
It's backwards compatible with regular PVST, so don't worry if all your switches aren't set the same right off the bat, but you should eventually get round all your devices and set this.
Next, try this:
Switch1(config)#spanning-tree vlan 1-4094 root primary
Switch2(config)#spanning-tree vlan 1-4094 root secondary
Switch2(config)#spanning-tree vlan 3 root primary
Switch1(config)#spanning-tree vlan 3 root secondary
I just tested this on my 6500s and it works fine - If you get an issue with the link going down again, on switch 1 do a "show spann vl 3" and see where it thinks the root bridge is... it should come back with the mac address of switch 2 - if not there's some other device on the network that is somehow claiming root - you can find it by following the root ports for that VLAN.
Failing that, can you post here the interface configs on both ends of your Switch1 - Switch2 Interlink?