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

[Leo Laohoo]

12.2(50)SE5

`nuff said. 

[acedsl]

Pardon me? I don't understand

[Leo Laohoo]

Pardon me? I don't understand

Apologies.  

I was making a snide remark about the IOS version currently being used because I  wouldn't recommend to anyone to use this particular train.

[acedsl]

Hm. Why? Is there anything in particular? Anyway which one you recommend to try?

[Leo Laohoo]

I'd recommend the latest 12.2(55)SE train because it is widely accepted and acknowledge that this is the most stable and reliable IOS version.

TIPS in choosing the right (or suitable) IOS version.

1. Look at the release date of the latest IOS.  If the date hasn't changed for >6 months, then avoid that particular version.  
2. Read the Release Notes.  Play close attention to the Open Caveats section.

[acedsl]

vlan 20 is passing over the trunk because the router does receive DHCPDISCOVER on vlan 20.

The phone is at remote location in customer's place. I can ask the customer to check something on the phone. Can you be more specific what I should have him to look for/at?

Thanks

[acedsl]

Yes, cdp is enabled, phone is able to determine it's voice vlan, 'cause DHCPDISCOVER arrives at correct vlan.

I did try to disable URPF, it didn't help. Out of despair I've also tried to remove all optional commands from the interface - nat, virtual-reassemnly, proxy-arp - leaving just ip address. That also didn't help.

It seems like for whatever reason the phone either doesn't receive or discards the router's DHCPOFFER.