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YIKES! Spanning-Tree Across Parallel Bridged WAN Links

Here's something that I wish I didn't have to ask! I have a remote site with two parallel WAN links, both *bridged* instead of routed, one faster than the other. I inherited this, it is one of the oldest WAN links in the network...

Please forget the fact that it *should* be a routed link (it's a *long* story). I'm stuck with it being bridged. Yes, almost 60% of the traffic is garbage broadcasts and LAT traffic that doesn't need to traverse the T1...

Anyhow, one link is a full T1, the other is a 368k FT1 (which is a backup link). Both are bridged. 2620's are on both ends of the T1. Old Vitalink TransLAN bridges *were* on the backup link, which have recently failed.

Before the TransLANs failed, they were manually enabled when the main T1 went down, and manually disabled when the T1 was restored. Now that they're gone, the solution is to put a pair of 1601R's on the backup link, and bridge them as well.

Another wrinkle is that at the remote site, both the 1601 and the 2620 attach to the same switch. At the central site, the 1601 attaches to one switch, and the 2620 attaches to another peer switch...

Finally, the same network segment spans both links, a portion of the central site, and nearly all of the remote site.

The question is how to set up Spanning Tree. I'd certainly like to keep both links up, so the T1 can automatically fail over to the backup link. But I also don't want to create a bunch of needless spanning-tree traffic, which would compound an already bad problem.

Reading through some of the documentation Cisco has, I have several ways to go, but naturally none speak to this exact scenario. I'm sure this would be an acedemic excercise anywhere else, but it's my reality!

If anyone wants to see a quick diagram to help visualize my situation, let me know. I can email you a quick diagram. Thanks in advance!

Jim

1 REPLY
New Member

Re: YIKES! Spanning-Tree Across Parallel Bridged WAN Links

I believe that if you configure the bridge on your 1600s and 2620s with default configuration, one link should be blocked. Please select one switch in central site as the root switch first.

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