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

[Tom Lanyon]

On 08/01/2010, at 6:53 AM, 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:
> <snip>
> 
> 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. 
> <snip>
> 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?

Hi Jared,

I've run into the same problem on our 3750Gs and 3750Es (running 12.2(46)SE) with no solution so far.

The log on our switches indicates that it's due to the config for the Port-Channel being different than the underlying Gix/y/z interfaces, which is not allowed, so it shuts the etherchannel down. I tried to work around this by adding the VLAN to all ports at once, eg:
	conf t
	int ran gi1/0/1, gi1/0/2, po1
	sw trunk allowed vlan add 400
	end

... but this didn't seem to help.

This has been a constant problem with earlier IOS releases too so I don't believe it's just 12.2(46) to blame. I assumed there was a simple solution, but hadn't had enough impetus to search for it yet.

Tom