On spanning tree and virtual router priorities
Work August 4th, 2008
I never seem to remember which way this goes, and usually when I need to look it up (like my network is in a weird state,) I can’t check to see how it “should” be. So this post is a reminder — at least on the Foundry equipment we’re currently running.
Spanning tree priorities — lowest number wins. (Unless set priorities are equal, in which case, I think the lower switch MAC wins.) In our environment, a 1000 weighted STP is the root over a 2000 weighted instance.
With VRRP-E, it’s the opposite. Higher priority wins. The default priority with our FI1500s is 100. Any backup priorities lower than that are secondary.
So, the “active” router should have a lower STP priority and a higher VRRP-E priority.
The “backup” router should have a higher STP priority and a lower VRRP-E priority.
Clear as mud.
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