wrong vlan to 7641 IP Phone

Unanswered Question


I have some 7941 IP Phones wich are connected to 3560 PoE switches (version 12.2), the phones were working just fine and suddenly they showed a message "registering..." I found out that the IP Phone had an IP address from the data vlan instead of the voice vlan although port configuration didn't change and it was correct, besides of checking the configuration I connected a 7911 IP phone to that port and it had no problem. What I did was configure that port to belong only to the voice vlan, the IP Phone registered perfectly, then I had to change the configuration back in order to have access to the data vlan from the PC. It happened only with this model. what I need to know is the cause of this behavior in order to avoid this happen again. I took a look at cisco.com and i found a similar case but with 7935, the tac collection sollution was K19769373.

I hope you can help me to find out the root cause and the solution. Thank you in advance.


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
chrcoope Fri, 10/23/2009 - 14:06
User Badges:
  • Bronze, 100 points or more

Hi Alex,

It sounds as though the switchports voice vlan is not configured. This document may help with that. I have attached a document with instructions to manually set the voice vlan which you may find handy for trouble shooting. Let us know if this helps or if there is more we need to look at like the phone loads.



thanks Chris,

I have this configuration in the switch port

interface FastEthernet0/1

switchport access vlan 3

switchport mode access

switchport voice vlan 13

spanning-tree portfast

the 7941 IP phone was working ok, suddenly it stops working, the message was "Registering" but it never finishes to register. I unplugged that IP phone and connected a 7911 IP phone and it worked just fine. That's why I configured the switch port to belong only to voice vlan and after the ip phone was succesfully registered I configured the port back. For some reason the 7941 IP phone receives an IP address from the data DHCP instead of the voice DHCP, what is weird since the phone is supposed to belong to voice vlan because of CDP.

So, I'd like to know what is the cause of this behavior in order to avoid it to happen again.

Thank you in advance for your help.


chrcoope Mon, 10/26/2009 - 06:44
User Badges:
  • Bronze, 100 points or more

Change switchport mode access to switchport mode trunk

Switchport mode dynamic desireable may also work. Make the above chance and let me know what the results are. I think that at this moment, your phone gets the appropriate voice VLAN information from CDP and starts tagging its frames but the "access port" drops them.



bnidacoc Tue, 10/19/2010 - 07:25
User Badges:

chrcoope, is "switchport mode trunk" the proper method to resolve phones not getting onto the right vlan?  Cisco's documentation, http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/54sg/configuration/guide/voice.html#wp1044179, seems to indicate that "switchport mode access" is still the proper method for configuring phones which also provide data services for a guest plugged into the phone.


chrcoope Wed, 10/20/2010 - 10:16
User Badges:
  • Bronze, 100 points or more


Access is correct with voice vlan set.



This Discussion