Spanning-tree issue

darren-carr · ‎05-12-2009

Hi Guys

I have got a weird issue. A switch I have nominated does not appear to be forwarding for a particular vlan over a trunk (please see below).

Port Mode

Encapsulation Status Native vlan

Gi0/46 on 802.1q trunking 1

Gi0/48 on 802.1q trunking 1

Po1 on 802.1q trunking 1

Po2 on 802.1q trunking 1

Port Vlans allowed on trunk

Gi0/46 1,31

Gi0/48 1-4094

Po1 1-4094

Po2 1-4094

Port Vlans allowed and active in management domain

Gi0/46 1,31

Gi0/48 1,30-31,71,73

Po1 1,30-31,71,73

Po2 1,30-31,71,73

Port Vlans in spanning tree forwarding state and not pruned

Gi0/46 1,31

Gi0/48 1,30-31,71,73

<strong>Po1 1</strong> (issue is here not forwarding VLAN31)

Port Vlans in spanning tree forwarding state and not pruned

Po2 1,30-31,71,73

The switch is connected to another switch using a 3Gbps etherchannel... but for some reason does not want to forward this vlan. It is causing another issue as a different interface on both switches then goes off to two other switches and certain devices attached to these cannot communicate (all on VLAN31). I think this is causing the issue but am not sure how to fix it.

I have checked the trunk links and the vlans allowed, etc but cannot see anything obvious?

Any ideas? Thanks

andrew.prince · ‎05-13-2009

post the output of "show span vlan 31" on the switch that is having the issue

andrew.prince · ‎05-13-2009

post the output of "show span vlan 31" on the switch that is having the issue

glen.grant · ‎05-13-2009

If this is a transparent setup make sure the layer 2 vlan for vlan 31 is created on each switch . Verify on each switch with the show vlan command and make sure vlan 31 shows active.

darren-carr · ‎05-13-2009

Guys

I shut down the portchannel between the two switches, re-enabled and the VLAN is now being forwarded over the switch.

Not sure why it stopped or if something caused a STP reconvergence or something...anyway.. all is good now... thanks for you input

Darren