Spanning-Tree Protocol

Hi guys (and girls ).

Last weekend we had some maintenance (upgrading switches) in the network.
Here we replaced some 3540's for 3750's (stacked) in the network... after a while we where done and starting testing.

Seems that there has been a Loop in our network and we can't figure out what the cause was.

anyone has any Idea's what could make a STP-enabled network still be subjective to loops?!

We use VLAN's, switched environments, HSRP, spanning-tree/portfast/bpduguards...

any scenario where we have STP and loop can occure would be welcome just for us to figure out how and what ...

thnx!

- I think the stp domain would be split up somewhere due to portfast and bpdu guard .

Check the portfast ports. Portfast effectively disables the STP action on those ports. If you had an existing config on those switches or had certain ports set to portfast then used them for something else in the heat of the changeover it's quite possible you could have come a cropper with an unforseen loop

It seemd the IOS on the 35xx couldn't support more then 64 vlan's... the remaining VLAN's didn't support STP so these VLAn's went into a loop... sometimes it's looking for a dime in a country