- Bronze, 100 points or more
I'm currently testing the 'spanning-tree bpduguard enable' feature on switch ports, and
have some doubts about it and the BPDU sending mechanism.
I have one switch (switchA) that is connected at the edge of the network, this switch as
one port Gi0/1 as Root Port. This switch has a free port, Fa0/35 that has the following
switchport access vlan 500
switchport mode access
spanning-tree bpduguard enable
I come with another switch (switchB with no more ports connected) and connect it to the
Fa0/35 of switchA.
SwitchA should put Fa0/35 in err-disabled mode. That doesn't happen, because switchB
(non-root bridge) is not sending BPDUs due to the fact that it received a better
configuration BPDU on his root port from switchA and updated his own configuration BPDU.
---> I would like to know wich switch send the first BPDU(!) <---
Case 1: switch A sends BPDU first
Expected result: SwitchB updates his configuration BPDU since his own is inferior and
doesnt send any BPDU towards root bridge; (this happens in 99,9% of the tests)
Case 2: switch B sends BPDU first
Expected result: switchA put his Fa0/35 in err-disabled mode; (this is what i would like
What is the correct behaviour and why? How can i achieve case2?