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New Member

Phones Not Receiving DHCP IP

Hello Experts -

We recently replaced our Call Manager servers, jumping from 4.1 to 7.1 after successfully running DMA backup/restore.

Most everything is working fine except when I've had to add a new ip phone to our system. The problem is that it cannot receive a DHCP ip address from the server.

I've checked all the settings that I can possibly find and everything looks like it is configured correctly. If I manually assign an ip to a phone (we are using mostly 7940's and 7960's), then the phone will boot and register fine and works like it should after flashing its image and getting the correct load and firmware.

Rebooting an existing phone in our environment (phones that were online when we had CM 4.1) will boot up more slowly, but it will finish and come online, so apparently it is caching that info from before.

The problem is with a new phone and the only way for me to get it to work is to manually assign the ip. No other changes were made to our environment, so I don't think it would be useful to try to capture any switch packets. I'm wondering if there is something I've missed with our DHCP setup.

Any advice would be appreciated. My TAC engineer basically gave up on me :-(

Everyone's tags (1)
2 ACCEPTED SOLUTIONS

Accepted Solutions
Super Bronze

Re: Phones Not Receiving DHCP IP

Hmmm... can't believe we all missed that one!

Well - maybe I'm still being a bit slow, but shouldn't the IPV4 Subnet Address be 10.0.0.0? Since the subnet mask is 255.255.0.0, the address 10.0.1.0 is actually a valid host address, not the subnet address.

I suspect the input validation on this config page is either not good or doesn't exist, but the back-end DHCPD service will be rejecting the config.

Set the subnet address to 10.0.0.0 and restart DHCP monitor. Then if it doesn't work... on my system events relating to the DHCPD are in syslog/messages, maybe monitor that for errors when you restart DHCP Monitor.

Regards

Aaron

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

Re: Phones Not Receiving DHCP IP

Aaron,

You are correct, it should be 10.0.0.0. Hopefully changing this and then restarting the DHCP monitor service will get this working.

Thanks,

Adam

41 REPLIES

Re: Phones Not Receiving DHCP IP

If you look in the phone settings when it is booting, does it get the correct VLAN?

Brandon

New Member

Re: Phones Not Receiving DHCP IP

Yes it does. The LCD shows "Configuring VLAN" before it goes to "Configuring IP" where it gets stuck and hangs.

Looking at the DHCP settings under Network Config just shows 255.255.255.255 and nothing for TFTP Server or Default Router.

Re: Phones Not Receiving DHCP IP

So, in network config, it shows the correct VLAN? Is the CUCM server providing DHCP? Is the DHCP service activated and running and a DHCP scope configured?

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/6_1_1/ccmcfg/b02dhsrv.html

Brandon

New Member

Re: Phones Not Receiving DHCP IP

Yes it is set to the same VLAN id as the others that are working and boot up fine. It bombs out when trying to get an IP, so CUCM DHCP is not running properly but the scope is set and the services are running and activated.

Re: Phones Not Receiving DHCP IP

Have you tried restarting the DHCP service on CUCM?

Brandon

New Member

Re: Phones Not Receiving DHCP IP

Yes, just tried it again and still no joy.

I saw in web doc (for an earlier version of CUCM) about DNS settings. Our previous 4.1 CM did not utilize DNS and our current ip phones boot up fine with DHCP enabled, but again, they seem have the required info cached.

I'm wondering if DNS is necessary?

I have to leave for an appt. but will be back later this afternoon and appreciate the help Brandon.

Hall of Fame Super Gold

Re: Phones Not Receiving DHCP IP

Phones may be sturdy at times.

Do reset sequence on them.

New Member

Re: Phones Not Receiving DHCP IP

Thank you, but I'm not sure what you mean by reset sequence? I've unplugged and reconnected the LAN cable which reboots the phone. I cannot perform any sequence to the device via CUCM as the phone is not registered.

Hall of Fame Super Gold
New Member

Re: Phones Not Receiving DHCP IP

That did not work. I don't think the problem is on the phone side, but rather something to do with the CUCM server itself, namely the Publisher as it

is the one running DHCP.

Hall of Fame Super Gold

Re: Phones Not Receiving DHCP IP

For a try, disable DHCP there, enable it on a router.

Do not worry about conflicting addresses, as router pings before assign.

Re: Phones Not Receiving DHCP IP

Have you taken a look at your system syslog? Launch RTMT and take a look. It will tell you if you have any scope conflicts or issues with the DHCP monitor service.

What is the IP address/mask of your publisher? What is the scope that you have defined?

I ran into a situation where I had my CUCM in the same class C address space as the DHCP scope that I was planning on using for the phones. After I added the scope, the phones would not pull an IP. When I took a look at the system syslog I saw the following error

Error Mesage: Warning: subnet 10.231.51.128/28 overlaps subnet 10.231.51.0/24

I am not sure why it was complaining about the 10.231.51.0/24 subnet when my CUCM cluster was in the 10.231.51.32/28 subnet and the DHCP scope was using 10.231.51.128/28.

I don't know if they is expected behavior or if it is possibly a bug within the DHCP server daemon. Since my setup was in a lab, I just changed the DHCP scope to 10.231.53.128/28 and everything was fine.

If this matches something that you are seeing, maybe you can take this to TAC.

Hope this helps,

Adam

Please rate if helpful

New Member

Re: Phones Not Receiving DHCP IP

Thanks Adam, that was helpful.

I was able to view the log and see that it was flagging a DeviceTransientConnection error. In fact, I'm getting TONS of these errors. So I've been researching that this morning, but it wasn't as helpful of a clue as I was hoping. Cisco docementation is fairly vague on this and says it could be a database error, or misconfiguration.

As far as our scope, we have a static 10.0.0.50 for our Pub and a scope of 10.0.1.100 - 254 for dhcp clients, so I don't see that overlap is my problem, nor am I getting that error in my logs.

Super Bronze

Re: Phones Not Receiving DHCP IP

Hi

DeviceTransientConnection just means something has opened a connection to CCM, then closed it - you get this (for example) a lot if you lost a remote site link, and the phones come up and register to one server before realizing a higher-order CCM is available etc... lots of scenarios generate this, so if you have any problems at all you are liable to see them...

I think at this stage with your problem I would be doing one (or both) of these and looking at the output:

1) Packet capture of the phone

2) Packet capture on the CCM (you can run a packet capture on the server using utils network capture and pull the file using RTMT)

The server cap may be very busy, so keep it short...

Regards

Aaron

Please rate helpful posts...

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: Phones Not Receiving DHCP IP

Thanks Aaron. The TAC tech and I did run a capture on the phone, but I'll get on on the server end and see if that helps. I'll post an update when/if I ever find a resolution to this.

If any other ideas, please let me know. Thank you.

Super Bronze

Re: Phones Not Receiving DHCP IP

Hi

What did the phone capture show you?

You presumably see a request go out; do you see anything come back?

Aaron

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: Phones Not Receiving DHCP IP

According to Cisco TAC, it showed that there was no response which indicated a problem with DHCP, but the exact problem from the capture was apparently inconclusive. I'll try to get one on the server this afternoon to see what I can find.

Super Bronze

Re: Phones Not Receiving DHCP IP

Hi

Yeah, sounds like the way forward - no reply from the server means:

1) didn't reach server

2) server didn't like the request (i.e. didn't match scope)

3) server response didn't get there

A cap should fill you in...

Aaron

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: Phones Not Receiving DHCP IP

This is the capture we got from the Publisher:

7709    142.424216    0.0.0.0    255.255.255.255    DHCP    DHCP

Discover - Transaction ID 0x7fae8ceb

The phone will also show the 255.255.255.255 for it's DHCP server. Not sure what to make of it.

Re: Phones Not Receiving DHCP IP

Would it be possible to post some screenshots of you DHCP server and scope configurations?

Thanks,

Adam

New Member

Re: Phones Not Receiving DHCP IP

Hopefully you can open this. Made with W7 snipping tool.

Re: Phones Not Receiving DHCP IP

It looks to me that your DHCP scope is setup incorrectly.

In the screenshot that you supplied, you have 255.255.0.0 in the 'Subnet IPv4 Address' field. That field is where you are supposed to enter the network address for your DHCP scope. Example: 10.0.1.0

I have attached what your scope should look like.

Thanks,

Adam

Please rate if helpful

New Member

Re: Phones Not Receiving DHCP IP

Thanks Adam, that was a good catch. Cisco is the one that set that up, but you're right, it doesn't make sense so I changed it. However, my phone is still not pulling an IP and I restarted the DHCP service as well as erased the config on the phone, yet again.

Super Bronze

Re: Phones Not Receiving DHCP IP

Hmmm... can't believe we all missed that one!

Well - maybe I'm still being a bit slow, but shouldn't the IPV4 Subnet Address be 10.0.0.0? Since the subnet mask is 255.255.0.0, the address 10.0.1.0 is actually a valid host address, not the subnet address.

I suspect the input validation on this config page is either not good or doesn't exist, but the back-end DHCPD service will be rejecting the config.

Set the subnet address to 10.0.0.0 and restart DHCP monitor. Then if it doesn't work... on my system events relating to the DHCPD are in syslog/messages, maybe monitor that for errors when you restart DHCP Monitor.

Regards

Aaron

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

Re: Phones Not Receiving DHCP IP

Aaron,

You are correct, it should be 10.0.0.0. Hopefully changing this and then restarting the DHCP monitor service will get this working.

Thanks,

Adam

New Member

Re: Phones Not Receiving DHCP IP

Aaron / Adam -

That did it! You guys are awesome man! Thanks so much for your help on this (and everyone else too). I thought we had to be missing something fairly basic, but Cisco TAC is the one who originally assisted with the config of the DHCP in the first place...

You guys should let Cisco know if you need a job. I'll put in a good word for you

Super Bronze

Re: Phones Not Receiving DHCP IP

Cisco? Wouldn't want to work there

Have to say it's a bit naughty of Cisco to throw a /16 subnet in for a CallManager, given that it will cave in if there are > 1024 devices on the subnet...

Good to hear it's working, credit to Adam for actually reading the screen grab properly!

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: Phones Not Receiving DHCP IP

I selected both your answers as the corect one so I hope that is refected in your

points/feedback properly.

Really, a big thanks once again guys.

-Brian

Super Bronze

Re: Phones Not Receiving DHCP IP

Can you post the actual capture file?

That's basically a headline, doesn't show the detail enough...

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
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