I have two 6509s both with single FWSMs running in transparent mode with bridged Inside and Outside VLANs.
I have my Core A set to STP priority of 8192 and Core B set to 16,384 to make Core A the root for all VLANs.
Problem I have is when I look at spanning-tree on Core A for Inside VLAN 324 it states to get to the Root go via PO100 (Cost of 9) and that the Root also has a Priority of 8192, but as the designated Root has a lower MAC address it's pointing to the etherchannel. PO100 is L2 Etherchannel between the Cores.
Moving accross PO100 to Core B and running the show spanning-tree command I can see that to get to the Root Bridge I need to go via PO272. PO272 is the internal Etherchannel to get to the FWSM on the Core B Switch. This shows a cost of 6 to get to the Root and a mac address of the Root Bridge which resides on Core A (Outside VLAN 124)
To give some perspectibe,theoutside VLAN of the pair has it's STP ROOT on the Core A switch as intended
Can you try specifying the stp root via the primary/secondary commands - spanning-tree vlan xxx root primary/secondary. instead of specifying the priority value, this will decrease its own priority value if another switch challange's for stp root with it present priority vlaue.
Also you could apply spanning-tree rootguardto protect your root switch designated ports becoming root ports towards a new stp root switch
To influence a directly connected downstream switch from the root to elect its stp root port use -spanning-tree vlan x port-priority x ( highest value less preferred)
To influence a local switch towards the root to elect its stp root port use - spanning-tree vlan x cost y ( highest value less preferred)
Welcome any other CSCr's to jump in here and correct me if i am wrong?
Please don't forget to rate this post if it has been helpful.
kind regards Paul
Please rate and mark posts accordingly if you have found any of the information provided useful. It will hopefully assist others with similar issues in the future
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