Phones will not pull address from DHCP

Here’s what happened…

Sunday we had a power surge bad enough to toast psu on a server. Server is back up (it runs dhcp server among other things). All machi es work correctly. No phone will pull address from the server. I have factory reset my desk set thinking that was it. No success. All phones are refurbished Aastra 55i handsets. Nothi g else changed and all equipment has been restarted.

Any suggestions? This is a head scratcher for me.

This should not be hard to debug. If you connect a PC in place of one of the phones, can it pull an address from DHCP? If yes, run Wireshark or tcpdump on the server and see whether requests from the phones are coming in and what responses, if any are being sent out.

If it can’t get an address from DHCP, configure the PC for static IP and see what network connectivity it has. If it can access other functions of the server, the DHCP server is apparently misconfigured. If the PC has no access to the server but can access other LAN resources and the internet, the server’s network connectivity is somehow broken.

If the PC can’t access anything, you have a bad switch or other element in the path between it and the router.

The phones are chained to the PC. So the PCs can all pull addresses from the server. I get the same thing when I plug a phone directly into the switch. It just sits at waiting for IP. I even pulled an extra out of a box (that wasn’t provisioned) to see if it would pull an address and nothing. If I unplug the LAN cable from the phone (essentially restarting it) the PC loses network connectivity until the process lets that switch in the phone run the pass through for the PC.

So…to answer your question…all PCs are fine once the server came back up. I have access to it and all other network resources. Mail server and file server are on that box as well as VMs and all services that were needed are up and running.

The Freepbx box is up and running and pulled its reserved address from that server as well. SIP trunks are running fine and we are getting messages and the pbx is sending those message out as emails as configured.

Are VLANs involved? If not, the server should be ‘seeing’ the DHCP Discover packets. Use Wireshark to see whether/how they are being answered. If the phones are using a separate VLAN, look at the switch configuration(s) to see whether the packets are being sent to the server (and whether replies are getting back to the phones).

No VLANs are involved. I didn’t see anything in the TCP dump when I tried to reproduce the error. Gonna look at wireshark next.

OK, so normal DHCP operation is:
Phone sends DHCP Discover
Server sends DHCP Offer
Phone sends DHCP Request
Server sends DHCP ACK.

Wireshark will show you what’s happening on the failed attempts. You can compare that with successful address acquisition by a PC and you should be able to figure out what’s going wrong.

What phone?

Did you enable DHCP on the server?

Are you sure the phone isn’t getting an address? In this case, you could get an address, but not get provisioning information because of a mis-configured option 66 in your DHCP setup.

Aastra 55i and 6731i phones. Basically all of them in the building.

Yes DHCP is on the server because all of my clients are able to get onto the network, ping server, get files from file server, etc.

The phone sits at ‘DHCP: Waiting for IP’

Option 66 is configured correctly on the server.

I also know that the server’s DHCP is correct because the reservation in the scope hit when I restarted the pbx server and it showed up correctly in the scope on the DHCP server.

OK. Next stop is probably the /var/log/messages file. “tail -F /var/log/messages” and see what the phones are doing with the DHCP requests. My assumption is that there’s something going on between the request and the address allocation, and the messages log file should give you a clue or two.

OK. Next stop is probably the /var/log/messages file. “tail -F /var/log/messages” and see what the phones >are doing with the DHCP requests. My assumption is that there’s something going on between the request >and the address allocation, and the messages log file should give you a clue or two.

My Freepbx server isn’t the DHCP server. My Windows DC is. Will that make a difference on this?

BTW…wireshark only shows the DHCP Discover for the phones. I don’t see the rest of them for the phone. I do see them for the PCs.

So your server isn’t responding to the phones? Check the addresses on the wireshark interaction and make sure the DHCP Discover isn’t getting jacked up…

Could be here a lot of things…

  • Old firmware version which can have DHCP issues.
  • Your DHCP server has no available IP’s
  • There’s a network routing issue etc.

I would temporarily stop the DHCP server on the Windows Server, and enable DHCP on the router, see if your phones are getting an IP.


This gave me yet another lesson in save, save, and resave configs. The switch reverted back to a saved config (that I thought was current). When the power bounced the switches…it turned back on the Auto-VOIP stuff that gave me such a hassle the first time. After I discovered that…I went back through and turned all of it off and phones started ringing. So it was the switches. And I didn’t have to reset…just turn off and SAVE, SAVE, SAVE the configs.

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