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

[Jared Gillis]

I see what you're thinking here, but I'm still not sure why adding a vlan to an existing trunk should ever cause a physical link to flap, or affect the underlying LACP session.

Harold 'Buz' Dale wrote:
> Check the other end to make the the LACP config is correct and maybe a "sh etherchannel" variation to look at what is going on. If the LACP is wrong maybe the trunk was carried over gi1/0/1.
> 
> Luck,
> Buz
> 
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jared Gillis
> Sent: Thursday, January 07, 2010 3:23 PM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] Adding vlan to port-channel trunk causes port-channel to flap
> 
> 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
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/