Greetings:
I have a configuration where I have two CSS attached to two WS 3550 switches. I'd like to connect an interface from each VLAN on each CSS to both 3550 switches (see attached). I have a problem when both of the interfaces are active in a VLAN. The spanning tree breaks down (both CSS see themselves as the root and one of the 3550's becomes the root for the two 3550's). Additionally, I had a situation where the ISL link between the 3550's shut down due to excessive spanning-tree errors.
I looked into using unconditional bridging, but that would cause problems on the "outside" interfaces as we can't predict how the VLAN's will be configured on that side of the CSS. We actually have a split situation where layer-3 path forwarding decisions are preferable on hte outside and layer-2 path forwarding descisions are preferable inside.
