[c-nsp] Port-channel configuration "stickiness"...

[Jeff Kell]

After a few IOS  updates in our maintenance window tonight, I had some
port-channel trunks fail to come up *again* and this is becoming more
than an occasional nuisance... perhaps others have seen this...

We run a number of port-channel uplinks between Catalyst switches
(3560s, 3750s, 4500s, 6500s) that are typically configured for LACP, and
have an associated "switchport trunk allowed vlan x,x,x" list on them to
only permit backbone vlans and keep local area user/server vlans within
their scope.  As we often have to tweak configurations to add additional
things in, they are subject to the periodic "switchport trunk allowed
vlan add x" changes.  We typically do this at the port-channel level,
and it propagates itself to the member interface configurations.

After an update such as tonight, sometimes the port-channel  will not
come up because of mismatched "allowed vlans" between the port-channel
and the individual members, e.g.,

> Jan 18 17:54:46.088 EST: %EC-5-COMPATIBLE: Gi2/0/47 is compatible with port-channel members (ServerFarm-2)

If you go back and tweak the interface configs to match the port channel
(or vice versa, sometimes one and sometimes the other are missing a vlan
or two) the port-channel comes up and the link is re-established.

I've seen this on 12.2(*) [various 50-series releases], and on 15.x new
releases.  Has not affected the 6500, it's just the upstream of some of
these channels.

Known bug?  Feature?  You can alter a port-channel configuration and
expect it to propagate to the members, correct?

Never had issues with this that I recall until more recent releases.

Jeff