[c-nsp] Adding vlan to port-channel trunk causes port-channel to flap

[Rick Coloccia]

I've run into flapping issues when adding a vlan if the vlan wasn't 
present upstream.  I don't know if this is your case, but in my case, I 
had two 6500 cores each attached to the same 3750.  port channels and 
spanning tree in place.  When I added a vlan to an interface on one 
core, the spanning tree went nuts because the vlan wasn't present 
everywhere it should have been.  My suggestion, then, is be sure the 
vlan you're adding is everywhere it needs to me.  I would have sworn I 
had my vlan everywhere, but I didn't, I'd missed in 1 place, so give it 
a look......

-Rick

Jared Gillis wrote:
> Hi all,
>
> I just ran into a strange problem on a 3750ME. I've got two gig ports in an active LACP port-channel looking like this:
>
> interface GigabitEthernet1/0/1
>  switchport trunk encapsulation dot1q
>  switchport trunk allowed vlan 101,102,400,664,1000-2999
>  switchport mode trunk
>  speed 1000
>  duplex full
>  channel-group 1 mode active
> end
>
> interface GigabitEthernet1/0/2
>  switchport trunk encapsulation dot1q
>  switchport trunk allowed vlan 101,102,400,664,1000-2999
>  switchport mode trunk
>  speed 1000
>  duplex full
>  channel-group 1 mode active
> end
>
> interface Port-channel1
>  switchport trunk encapsulation dot1q
>  switchport trunk allowed vlan 101,102,400,664,1000-2999
>  switchport mode trunk
> end
>
> When I added vlan 400 to the trunk allowed vlan list, one of the underlying gig ports flapped, which caused the port-channel to flap as well. 
> Jan  7 12:09:27.647 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to down
> Jan  7 12:09:27.656 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to down
> Jan  7 12:09:28.654 PST: %LINK-3-UPDOWN: Interface Port-channel1, changed state to down
> Jan  7 12:09:31.464 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to up
> Jan  7 12:09:32.454 PST: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up
> Jan  7 12:09:33.461 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up
> Jan  7 12:09:48.745 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan400, changed state to up
>
> This definitely seems like something that should not happen. I'm running Cisco IOS Software, C3750ME Software (C3750ME-I5K91-M), Version 12.2(46)SE, RELEASE SOFTWARE (fc2).
> Any thoughts on what I should be checking?
>
> --Jared
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-- 
Rick Coloccia, Jr.
Network Manager
State University of NY College at Geneseo
1 College Circle, 119 South Hall
Geneseo, NY 14454
V: 585-245-5577
F: 585-245-5579

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