Cisco IP Communicator DHCP for TFTP servers fails

[nigel.wensley]

I can't get Cisco IP Communicator to find TFTP servers by DHCP when it starts up on the Wireless LAN. It works fine on the Wired LAN.

The Wireless LAN is otherwise working fine. Clients can get an IP address by DHCP and use the network normally.

When I start Cisco IP Communicator:

- on the Wired LAN a DHCP Inform is sent by the client, proxied by the LAN switch, replied to by the DHCP servers.

- on the Wireless LAN a DHCP Inform is sent by the client, but dropped by the Wireless LAN Controller as shown below:

*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP received op BOOTREQUEST (1) (len 556,vlan 40, port 13, encap 0xec03)
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP option len (including the magic cookie) 320
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP option: message type = DHCP INFORM
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP option: 61 (len 7) - skipping
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP option: 12 (len 15) - skipping
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP option: vendor class id = Cisco Systems, Inc. IP Phone (len 29)
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP option: 55 (len 7) - skipping
*DHCP Socket Task: Apr 13 11:12:31.203: 00:1c:25:1a:a3:d6 DHCP options end, len 320, actual 74
*DHCP Socket Task: Apr 13 11:12:31.204: 00:1c:25:1a:a3:d6 DHCP dropping packet (no mscb) found - (giaddr 0.0.0.0, pktInfo->srcPort 68, op: 'BOOTREQUEST')

I can see in Wireshark that the option: 55 Parameter Request List contains option 66: TFTP Server Name and option 150: TFTP Server Address.

Could the problem be that this DHCP Inform has a source MAC address 00:1c:25:1a:a3:d6 which belongs to the Wired port which is disconnected? When I capture a successful Wireless DHCP Request in Wireshark the source MAC address is 00:13:e8:e1:79:61 the Wireless network adapter.

[dmantill]

First at all, let get some more details... Like who is the DHCP server?Microsoft? IOS? WLC?

Then Are you using DHCP relay?

If you are seen wireless packet captures going out with the ethernet nic MAC addres.. then either Windows is acting as usual... (crazy) or maybe if I am not wrong there is an option to setup the interface thru the one you want the IP communicator to use to connec to the CCM.Please make sure that you disable the wired interface while using the wireless only.

Try disabling the DHCP relay if you can and then see if you can get an IP address and check according to windows what is the IP address of the DHCP server, if still using the WLC dhcp relay, you will see the virtual IP adress, if not then you should see main DHCP server...

If still failing please let us know more details, like OS, IP communicator, WLC configuration, H-reap ? , etc...

[nigel.wensley]

The Wireless LAN Controller is configured to DHCP relay to a Microsoft 2008 DHCP server.

The Cisco IP Communication has a Network Preferences section in which an adapter to generate a Device Name must be chosen, and TFTP servers either selected by "default" i.e. DHCP, or specified.

The adapter options are the Wired or Wireless adapters. You can also manually set the Device Name and not base it on adapters.

If I disable the Wired network adapter altogether the Cisco IP Communicator refuses to send a DHCP Inform at all to find TFTP servers. I have tried with all the different possible Device Name settings.

So it seems the Cisco IP Communicator insists on using the Wired adapter MAC address as its packet source when sending a DHCP Inform.

Presumably because the Wireless LAN Controller has no information about that MAC address being registered on the network and allocated an IP address already, it drops the DHCP Inform.

[Tony Greensmith]

Hi,

Was there ever an answer to this?  I am experiencing the exact same problem, same packet capture information.

Thanks,

Tony.

[Stephen Rodriguez]

I would try disableing DHCP proxy, and making sure that an ip helper is configured under the L3 interface.

***If the WLC is the DHCP for any WLAN you can not disable proxy***

Steve

[Tony Greensmith]

Thanks Steve, I will give the DHCP proxy disabling a go however I think I have already been there (will have to check mountains of test documentation )

We have IP helper configured on the VLAN for the SSID.

As Nigel mentioned, packet captures seem to show that the IP Communicator software wants to use the wired MAC for these packet types even if not in use.

Tony.