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New Member

Question about IRB/spanning-tree


I have heard that it is necessary to disable spanning tree on bridge-group interfaces when configuring IRB. I was able to get IRB working in our lab. I had spanning tree disabled then later enabled, but I could not see any difference in behavior.

Could someone tell me why it is necessary to turn off spanning tree on IRB bridge-group interfaces?

New Member

Re: Question about IRB/spanning-tree

That doesn't seem to make sense. Once you're bridging, you better make sure there is a STP running

or that you will never have a loop possibility in the network.

New Member

Re: Question about IRB/spanning-tree

Yes, it seems counter-intuitive. I have been doing some reading and testing on this, though, and it seems the concern is spanning-tree causing instability in the bridging topology. For example, STP could cause the root bridge designation to change from one router to another in a simple point-to-point connection. I guess the upshot is that you should leave STP on, then see if "show spanning-tree" reports any topology changes. If it does not report any changes, you may as well just leave it off.