┌─────┐ ┌─────┐ | A ┼------┼ B | └─────┘ └┬───┬┘ └---┘ <-- loop
behold the above drawing. this is a test setup connectin switch A and B, and a test loop
A: cisco switch with rstp
spanning-tree mode rapid-pvst spanning-tree portfast default spanning-tree portfast bpduguard default
switchport mode access udld port aggressive
B: alcatel lucent omniswitch
- as dumb as possible
- passes all traffic
- no stp
- filters bpdu (default setting, not kidding)
when i create the loop on B, the whole system just drowns in a broadcast strom (because switch B filters the bpdu).
but when I change the port setting on A to a trunk (no other changes), stp does kick in.
switchport trunk encapsulation dot1q switchport mode trunk switchport nonegotiate
why? i don't understand, can somebody pleas explain this to me? and can I protect my network against this 'feature' of alcatel lucent? (besides putting all my port's in trunk)