Solved

Cisco IP Phone 7931 DHCP release

Posted on 2011-02-22
19
1,130 Views
Last Modified: 2012-05-11
Hello everybody!

 

We've got 7931 Ip phones which release their DHCP for voice VLAN and start getting addresses from access VLAN. Other types of phones work fine. I've configured SPAN to track the packets coming from the phone, and I see that IP phone starts sending DHCP requests all of a sudden.

 

As far as know, IP phones receive voice vlan information through CDP, may be it has anything to do with CDP exchange between the phone and the switch.

 

Thank you in advance!
0
Comment
Question by:fgasimzade
  • 9
  • 9
19 Comments
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Is there anything different in the configuration of the switchports to which those phones are connected?
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
No, nothing, I just found its a bug CSCsu70484
0
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Always great when things get buggy :-~

Anyway, glad you found it.
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
Ooops, sorry, that bug is for 7937 Ip Phones..
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
The issue is still persists.. Not only 7931, 7911 and 7965 act the same way.. They get IP from data vlan and then change it to voice vlan
0
 
LVL 35

Accepted Solution

by:
Ernie Beek earned 500 total points
Comment Utility
Ok, allthough it's not a (documented) bug did you try upgrading to the newest firmware? Or do you allready that.
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
Yes, I have upgraded the firmware on a number of devices, looks like it works fine now. Will watch these devices for a couple of days.. However, I noticed the same behavior for 7911 phones on different switch (so it is not a switch issue) but on the same DHCP server. Can it has anything to do with DHCP server?
0
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Could be. Is the DHCP server serving both scopes (voice and access)?
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
Yes.

Another thing I noticed is that Ip Phones occasionally obtain IP addresses from data VLAN and then immediately  from voice vlan. But they dont release data vlan ip addresses since I can see their mac addresses in data vlan pool on the DHCP server

Can you somehow explain me ip address obtaining process for Ip Phones. Do they initially receive data vlan ip and change it to voice vlan when they receive CDP from the switch?
0
How to run any project with ease

Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
- Combine task lists, docs, spreadsheets, and chat in one
- View and edit from mobile/offline
- Cut down on emails

 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Could you show me an example of how a switchport (for a phone) is configured?
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
yeah, sure

interface FastEthernet1/0/5
 switchport access vlan 2
 switchport mode access
 switchport voice vlan 160
 srr-queue bandwidth share 10 10 60 20
 srr-queue bandwidth shape  10  0  0  0
 mls qos trust device cisco-phone
 mls qos trust cos
 auto qos voip cisco-phone
 spanning-tree portfast
end

There was no config change before this issue arised
0
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Ok, just checking.

So it still looks like a server issue.

About the CDP:

When a Cisco phone is powered up, you will see the mute, headset and speakerphone indicators light up. Next, the phone and switch exchange Cisco Discovery Protocol (CDP) data. CDP is a Cisco proprietary protocol that lets interconnected Cisco devices learn about each other. The switch uses CDP to tell the phone which VLAN will be used for voice traffic. (Note: if you are not using separate VLANs for voice and data traffic, we need to talk!) During this process the phone will display "Configuring VLAN."

Once the phone knows which VLAN to use, it will tag all of its data frames with the appropriate 802.1q tag and request an address from the DHCP server. The phone will display "Configuring IP." The DHCP server will offer an IP address as well as the address of the TFTP server.


Got this from: http://www.enterprisenetworksandservers.com/monthly/art.php?1158

So before anything else the phone is told which vlan to use. That should mean that the DHCP server is giving out addresses from the wrong scope (or both as you told).

I can remember a similar case. There the DHCP server also gave out addresses in the wrong scope. If I remember correctly, the issue there was solved by giving the switches voice vlan interfaces an ip address as well (in the voice range but outside the scope ofcours). That way the DHCP server was able to see what scope to use.
Perhaps that's something to look at.
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
Thank you for your response!

We have IP address configured on voice vlan interface.

0
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Just so I don't misunderstand:

You allready had the vlan interface configured with an ip address on every switch?

Like
Interface vlan160
   ip address x.x.x.x
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
No, no, just on the switch connected to our DHCP server. Voice vlan interface with ip helper-address configured
0
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Well, if you have some addresses left on the voice vlan it might be an idea to implement that on all the switches.
0
 
LVL 18

Author Comment

by:fgasimzade
Comment Utility
The thing is that IP phones with this behavior are connected to the switch DHCP servers is connected to
0
 
LVL 35

Expert Comment

by:Ernie Beek
Comment Utility
Ehr, wasn't that what I suggested along the way (ID: 34958877)?
0

Featured Post

IT, Stop Being Called Into Every Meeting

Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

Join & Write a Comment

Every year the snow affects people and businesses. According to the Federation of Small Businesses (FSB), in 2009, UK businesses lost an estimated £1.2bn (http://news.bbc.co.uk/1/hi/business/7864804.stm) because of bad weather. This article was c…
Article by: user_n
How Sip Phone (User Agent) works and communicates with sip servers 1.  There is a sip server and a sip registrar.  The sip server and sip registrar can be one server or two different servers. The sip registrar is the server on which it is record…
Excel styles will make formatting consistent and let you apply and change formatting faster. In this tutorial, you'll learn how to use Excel's built-in styles, how to modify styles, and how to create your own. You'll also learn how to use your custo…
In this tutorial you'll learn about bandwidth monitoring with flows and packet sniffing with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're interested in additional methods for monitoring bandwidt…

728 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

9 Experts available now in Live!

Get 1:1 Help Now