Cisco IOS DHCP server problem: ip phone can't get an ip

[acedsl]

Hello,

I'm sorry to ask such a probably basic question, but I'm at loss.

I have a very trivial setup: router (3825, IOS 15.0(1)M10) - switch (3750, IOS 12.2(50)SE5) - ip phone (7962, firmware SCCP42.9-3-1SR3-1S)

For some reason the phone can't get ip address and I have no clue why. It looks like it discards router's DHCPOFFER.

Here's what I'm getting in debugging after phone powering up:

c199-41133#

Aug  7 14:35:50: DHCPD: client's VPN is .

Aug  7 14:35:50: DHCPD: DHCPDISCOVER received from client 010c.d996.9043.99 on interface GigabitEthernet0/0.20.

Aug  7 14:35:50: DHCPD: Sending DHCPOFFER to client 010c.d996.9043.99 (10.10.15.38).

Aug  7 14:35:50: DHCPD: broadcasting BOOTREPLY to client 0cd9.9690.4399.

c199-41133#

Aug  7 14:35:54: DHCPD: client's VPN is .

Aug  7 14:35:54: DHCPD: DHCPDISCOVER received from client 010c.d996.9043.99 on interface GigabitEthernet0/0.20.

Aug  7 14:35:54: DHCPD: Sending DHCPOFFER to client 010c.d996.9043.99 (10.10.15.38).

Aug  7 14:35:54: DHCPD: broadcasting BOOTREPLY to client 0cd9.9690.4399.

c199-41133#

Aug  7 14:36:02: DHCPD: client's VPN is .

Aug  7 14:36:02: DHCPD: DHCPDISCOVER received from client 010c.d996.9043.99 on interface GigabitEthernet0/0.20.

Aug  7 14:36:02: DHCPD: Sending DHCPOFFER to client 010c.d996.9043.99 (10.10.15.38).

Aug  7 14:36:02: DHCPD: broadcasting BOOTREPLY to client 0cd9.9690.4399.

The config is very basic, subnet is directly attached, no dhcp relays:

Router:

ip dhcp pool DHCP-VOIP

   network 10.10.15.0 255.255.255.0

   default-router 10.10.15.1

   dns-server 10.10.15.1

!

 interface GigabitEthernet0/0.20

 description VOIP VLAN

 encapsulation dot1Q 20

 ip address 10.10.15.1 255.255.255.0

 no ip redirects

 no ip proxy-arp

 ip verify unicast source reachable-via rx 1

 ip nat inside

 ip virtual-reassembly

 !

Switch:

 Interface FastEthernet2/0/8

 description Universal computer/phone port

 switchport access vlan 10

 switchport mode access

 switchport voice vlan 20

 spanning-tree portfast

I did some googling, I found several people complaining about similar problem, but no solution.

Does anyone have any idea what might be wrong here or how to further troubleshoot it?

Thanks a lot,

Michael

[paul driver]

Hello

Do you have cdp enabled?

conf t
cdp run

int x/x
cdp enable

Also I see you have uRPF enabled.

show ip verify statistics

Have you also tested without this?

res
Paul

[Julio E. Moisa]

Additional to Paul's comment, you also should consider use the 150 option under the DHCP, it is useful to be able to communicate with the TFTP in order to download the voice information.

https://supportforums.cisco.com/discussion/11535821/option-150-ip-xxxx-under-dhcp-pool-using-cisco-phones

[acedsl]

It's of course useful to communicate with tftp, but first the phone must obtain an ip address and that's where the problem is. For some unknown reason this very basic configuration - that works in hundreds of other places - doesn't work here. I'm completely at loss and ready to take any suggestion.

Thanks

[Julio E. Moisa]

Hi,

Do you have DHCP snooping configured on the switch?, try to connect a PC to verify if it obtains IP address otherwise try an IP manually and check connectivity with the gateway. 

[acedsl]

dhcp snooping isn't enabled. There are many other devices on the switch that obtain ip addresses just fine from this same router.

I did see this problem several times before, but never was able to troubleshoot it. Then I was just forced to put static ip and move on. This time customer has a little patience and I have some limited option to troubleshoot it.

I really was hoping that someone has already seen something like this.

[Julio E. Moisa]

Hi,

I have seen in other situations (other manufacturers) configuring manually the VLAN on the IP Phone, once the vlan is configure it will obtain IP addressing. 

[acedsl]

But in this case I did try to remove "switchport voice vlan" command, so that phone is placed directly into access vlan, voip traffic isn't tagged, no vlan negotiation takes place. It didn't change anything.

Have no clue. Any more ideas?

Thanks

[Julio E. Moisa]

Assuming the vlan 20 is passing over the trunk to the router, have you verified if DHCP option is available on the IP phone?

I found this link but I am not really sure it is the problem unless there is something blocking.

https://supportforums.cisco.com/discussion/12604916/cisco-ip-phone-not-getting-dhcp-address

[Julio E. Moisa]

Check this link:

https://supportforums.cisco.com/discussion/12463346/cisco-phone-not-getting-ip-address

also Im checking similar problem discussed on the community:

https://www.google.com/search?q=cisco+ip+phone+dhcp+problem+site:supportforums.cisco.com&client=firefox-b&sa=X&ved=0ahUKEwj8ydvrmcbVAhUmzoMKHZvtDQkQrQIIMygEMAA&biw=1366&bih=659

[acedsl]

Thanks, I'm reading through this. So far I haven't seen any solutions.

I also tried to configure option 150:

options 150 ip 10.10.15.1

Didn't help.

[Leo Laohoo]

Plug a computer to the port and assign the port to VLAN 20.  Does the computer get the IP address for the phones or not?

[acedsl]

Yes it does. Like I said before DHCP is functioning fine for multiple other devices connected to this same switch and getting DHCP from this same router.

[Leo Laohoo]

Like I said before DHCP is functioning fine for multiple other devices connected to this same switch and getting DHCP from this same router.

I want to know about getting the IP address with the phone VLAN. 

Ok, if the computer is getting an IP address on the phone VLAN, then look at the phone.  Look for the Status All and look at the error message being thrown by the phone.  

Would also be worthwhile to factory-default the phone.

[acedsl]

I understand. Like I said computer is getting ip address on the phone vlan. i also tried to move phone to the data vlan where all other devices live and it still couldn't get an ip address.

The phone doesn't boot. The phone is at the customer location and according to the customer it keeps saying "Configuring ip address" forever. "show ip cdp nei detail" shows that phone doesn't have an ip address. DHCP debugging looks like phone either not receiving or not recognizing DHCPOFFER. No other errors on the screen.

I'll try to advice the customer to do factory reset. Any more ideas?

Thanks