Voice VLAN devices getting data vlan IP

Unanswered Question
Apr 19th, 2010

Ok this is a weird problem. My Cisco phones at random times (days or weeks)

and random phones (different buildings) are getting a data vlan IP address.

The phones are still up and when a user can receive (phone rings) and call

other extensions but when they connect the phone goes busy. If you power

cycle the phone it will receive a new IP address on the voice vlan. I think

it is losing the voice vlan IP and getting the data vlan IP when the lease

is up and it tries to request an IP again. But like I said if you power

cycle it will get the voice vlan IP, confused.


I am assuming this is a routing program since it is coming across vlans to

get the data vlan IP. We have 2 separate vlans on 2 different DHCP server.

The data vlan DHCP server is windows server 2003 and the Voice vlan is

currently on our cisco 4507r. We did have a server 2000 box with the

DHCP server for the voice vlan but changed it when we had the phone system

upgrade. I had ip helper-address pointing to the DHCP server and still had

phones getting a data vlan IP.


The 4507r is the core of the network. The Cisco Voice servers are connected

to the gi eth ports on the 4507. The data vlan DHCP server is also connect to

the gi eth ports on the 4507r. The vlans are configured for the ports.


It is only happening with Cisco IP Phones 7970 series phones.


We have had this problem since before I started here about 2 years ago. We have

updated the phones verions several times without out a resolution. Also we

recently upgraded to CUCM to the latest and still have this problem. The phone

vendor is looking into this still but I thought maybe there was traffic issue

or a route confusion somewhere that might be a vlan or routing problem.


I am lost and do not know where else to look to try and trouble shot this.

I have this problem too.
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CHRIS CHARLEBOIS Mon, 04/19/2010 - 09:41

How are your switches configured ("switchport voice vlan" or manually configured dot1q trunks)?  Are all of the effected phones on a particular switch?  Why do you need an IP Helper command?

What you describe can be caused by VLAN leakage, when misconfigured Native VLANs cause traffic from one VLAN to seep into another VLAN.  It can also be caused by IP Helper commands, so I'm courious how those fit into all of this.

jmaurer1205 Mon, 04/19/2010 - 10:45

The switches are configured

4507r client ports

switchport access vlan 10

switchport mode access

switchport voice vlan 172

qos trust cos

qos trust device cisco-phone

tx-queue 3

priority high

shape percent 33

spanning-tree portfast

service-policy output auto-qos-voip-policy

3560 client ports

switchport access vlan 10

switchport trunk ecapsulation dot1q

switchport mode access

switchport voice vlan 172

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

queue-set 2

mls qos trust device cisco-phone

mls qos trust cos

auto qos voip cisco-phone

spanning-tree portfast

The ip helper was just a troubleshooting step. Thought I forward all the request to the DHCP server that it needed to receive the IP address. I currently do not have it on.

The Native VLAN 1 is used for all the VLANs.


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