Cascading 3550-24 with GBICs

[macansy7]

We are cascading 4 * 3550-24 switches with Gigastack. The top and bottom switches connect to two seperate 4507R Layer 3 switches using GBICs that have EtherChannel configured between them.

We are running Rapid Per VLAN Spanning Tree (rPVST+)on the switches. Should we adjust the Forward delay, Max Timers etc on the 3550's? Spanning Tree does not seem to be working properly and it takes a long time to converge - Thanks

[smcquerry]

How are the Gigastacks connected physically connected to the other switches? Are you clustering the switches? By a long time do you mean 30-50 seconds?

Without knowing more details, what I think you are seeing is a result of a shared-link in rPVST? When using rPVST all the links should ideally be full-duplex and showing as point-to-point. When this is the case he timers are irrelevant. If you have shared links (which I suspect the gigiastack ports to be) then you may need to configure those links as point-to-point.

http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12119ea1/3550scg/swstp.htm#96183