PVST in Nexus: allowed vlans and BPDUs

[FelipeRivera]

Hello world!

I do have the following question:
Will a trunk port with allowed vlans  1, 2 and 3 still send BPDUs of vlan 4 ?

The switch is a Nexus 5k and it's running pvst+.

Normally I woudl think It wouldn't, but im seeing them in wireshark.

[Georg Pauwen]

Hello,

to my best knowledge, the only way to actually stop BPDUs being sent across a trunk is to use pruning. Otherwise, BPDUs are sent for each VLAN that exists on the switch...

[omz · Accepted solution]

R1(config-if)#do sh int tru
Port        Mode             Encapsulation  Status        Native vlan
Et0/0       on               802.1q         trunking      1
Port        Vlans allowed on trunk
Et0/0       1-4094
Port        Vlans allowed and active in management domain
Et0/0       1-4
Port        Vlans in spanning tree forwarding state and not pruned
Et0/0       1-4
R1(config-if)#

R1(config-if)#do sh int tru             
Port        Mode             Encapsulation  Status        Native vlan
Et0/0       on               802.1q         trunking      1
Port        Vlans allowed on trunk
Et0/0       1-3
Port        Vlans allowed and active in management domain
Et0/0       1-3
Port        Vlans in spanning tree forwarding state and not pruned
Et0/0       1-3
R1(config-if)#

I am not seeing BPDU's for VLAN 4 if it is not allowed on the trunk.