7940 phone fails to get ip address from gateway router

[John Cheetley]

Hi Cisco techs,

I think I asked this question before but couldn't find a history of it

And please let me know is this is in the wrong area

Registered 7940 SIP phone in CUCM 7.2.1

Goes through boot up but not getting IP address from gateway router that has DHCP enabled with range 192.168.20.xxx 

2691 router can see the gateway via traceroute shows.

[Leo Laohoo]

Is DHCP option 150 enabled?
Is Voice VLAN in shutdown?
is this the only one that's having a problem or is it affecting all the phones?

[John Cheetley]

Hi Leo, Sorry about my late reply. Just lost access to the CUCM GUI. Is no dhcp on CUCM. Was going to use router gateway (connected to ISP) that has IP of 192.168.20.1and DHCP. Was going to use ip helper but realised this is for different subnets so that wouldn't work Voice vlan isn't shutdown This is the only phone having issues. Stuck on configuring IP Router IP address 192.168.20.2 is attached to fa0/0 (ip nat outside) that connects to ISP gateway router fa0/1 (ip nat inside)connects to switch but no ip address for this

[Leo Laohoo]

Cisco phones need to have DHCP Option 150 enabled.  This will enable the phones to "know" the IP address of the TFTP server is so the phones can download the firmwares and other associated files required for the phones to work.

DHCP option 150 can be enabled on the router.  

[John Cheetley]

OK now. Before we progress.

The router ip address should be allocated to the ip nat inside part. Not the ip nat outside. As the ip nat outside is for the external ip address ie the ISP?

[Leo Laohoo]

IP NAT outside means router looking at the ISP. IP NAT inside means router looking inside your network, like phones, printers and computers.
So the voice VLAN should be part of the "inside" and the ISP should be providing DHCP inside your network (only up to the WAN link).

[John Cheetley · Accepted solution]

That's cool. Phone now has IP address. Had to manually adjust the settings. Now is stuck on configuring CM list. Wasn't able to adjust these on the 7940 phone. Though I used **# and un-padlocks the settings. The CM listings can't be updated. And another thing. The config files for this phone type aren't in the tftp database. Used file list tftp * page. Was looking for XMLDefault.cnf.xml. , SIPDefault.cnf The phone is using a Universal Application Loader

[John Cheetley]

Phone has IP address though. Will try to ping tonight via CUCM and check why CM list further.