[cisco-voip] Phones on wrong VLAN?

[Jon Carnes]

We had a very similar problem that we traced down to the phones having
CDP turned on. Say what you will but once we turned that off, everything
worked as expected and the phones stayed on the proper Vlan and strayed
no more to the data side.

The client has several used pieces of Cisco hardware on site. One or
more of them may be sending misleading info about the network to the
phones - the client did not give us access to the network so that's just
a guess. 

Jon Carnes
FeatureTel - North Carolina's VoIP Provider for Business

On Wed, 2005-06-15 at 13:47, Mike Newell wrote:
> We have a weird problem...
> 
> About 10% of our phones on one of our networks get the wrong VLAN when
> they boot up.  If we continually reset them eventually they get on the
> right one; then every now and then one will spotaneously flip back over to
> the wrong VLAN again.  We've opened a TAC case (#601492441) but so far
> their recommendations point to errors that have conditions unrelated to
> ours...
> 
> In specific we have a bunch of 7970s attached to a pair of Catalyst 6509
> switches.  The ports are set up in dual-access mode with a voice and
> access VLAN set.  As far as we can tell data throughput on the ports is
> reasonably light; no broadcast storms, dropped packets, etc.  The phones
> are never in use when they flip (usually they flip in the night; bored
> maybe?)  We're running 6.0.2SR1.
> 
> What we see happen is the phones issue a DHCP request on the access VLAN
> (not the voice VLAN).  The DHCP server cheerfully gives them an address
> and they register.  After a while they seem to figure out they are in the
> wrong VLAN and switch to the voice VLAN, issue a DHCPRELEASE for the
> original address, then re-register with the new address.
> 
> The really weird thing is it's not consistent.  It's only happening with a
> few phones, and then only occasionally.  It's often enough to be annoying
> but not often enough to force us to upgrade all the phones (we have a long
> painful process for putting out new software releases, and they JUST NOW
> finally ordered our lab).  It doesn't happen at all with any of our phones
> connected to our 3560 switches.
> 
> Anyone seen this?  Any ideas???
> 
> Thanks!!
> 
> Mike
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