STP - Forcing the Default Path

[g.portellas]

Hi Guys,

I have implemented STP onto our l2 network - I now want to force a switch within the loop to use another path as apposed to the one selected by STP. I have configured the Port-priority with my prefered int having a higher priority but the switch still places that interface into blocking. I am assuming this is becuase it's selected path has fewer hops. My reasoning is that there is a heavier traffic load on that link and want this traffic to primarily use the alternate link.

My Question is how can I force the path chosen by STP.

thanks

Gary

[amit-singh]

Hi Gary,

STP has the following criteria for putting up the redundant link in the blocking or forwarding state.

1. Checks the neighbor with the lower MAC-address and puts the link in forwarding for the neighbor which has lower mac-address.

2. Lowest root path cost to the root.

3. Lowest port ID+ Port priority value.

Just change the root path cost of the undesired link to the higher cost and it will put that link into blocking state.

http://www.cisco.com/en/US/partner/products/hw/switches/ps646/products_configuration_guide_chapter09186a0080403f7b.html#wp1149907

HTH,

-amit singh