VOIP Phone reset after DHCP lease expires on wireless bridge


Nov 6, 2012
A few months ago we installed a new Mitel 5000 HX controller. Throughout I will refer to two locations Building A and Building B.

Building A contains all the network equipment. Switches, routers, server, and phone system. Building A is also where the Internet connection comes in as well as the phone lines from the PSTN. In Building A they have a Mitel 5000 HX controller with 2 LSM-4 loop start module 13 8528 digital phone (non-IP), and and 5340 IP phone.

In Building B they have a total of 5 Mitel IP phones. A 5324, 5312, 5340. (2) 5304 and one computer.

The buildings is connected together with two Engenius EN500 in a AP Client bridge mode. The AP Bridge is about 200 feet apart and has line of site communications. The speed is excellent across the bridge is excellent delivering Internet speed tests any where from 25Mbps to 60Mbps. ‘

So here is my problem.

The 5 IP phones in Building B reset every time their DHCP lease expires. The IP phone in one IP phone in Building A does not reset. So I’m thinking it has something to do with DHCP running across the wireless bridge. They will reset like clock work every 24 hours which coincides with their DHCP lease. Their DHCP server is a Linksys E300 wireless AP / router / firewall. I am not real comfortable about this being their DHCP server but it is the best solution at this time till they can get a real server.

In Building B they are running off a brand new POE Netgear switch, which we just replaced because their old one overheated and died. This new switch is running very nicely and handling things very good. It also runs very cool.

Here is what we have done to troubleshoot the problem so far. We have swapped out both Engenius access points. They used to run a pair of EOC2611P, which run on 2.4Ghz. We found that they were extremely slow because of all the 2.4Ghz signals in the area. A site survey revealed about 30 other AP in their range. We were having all kinds of problems with the network dropping and it being extremely slow. We put in the ENH500, which are 5Ghz AP’s, and it took care of the problem. A site survey revealed only one AP in the area and we placed the wireless bridge on a channel that was more that 40Mhz away from the other AP we found on the site survey.

By the way if anyone needs detailed info on how to setup Engenius AP’s in a bridge configuration I have created a cheat sheet that is very simple. You can have it setup in just a few minutes. The manuals from Engenius are horrible and do not give specific examples on how to setup the AP’s for different operations. Anyone wishing to have this document just let me know and I will send it to you.

We can pull the phone logs off the Mitel 5000 and see that the extensions in building B go offline and back online within a minute or less. We went on site to see what happens to the phones when they when the errors are generated in the log. Like I said it is like clockwork according to their DHCP lease. Watching the phone screens it says some thing to the effect DHCP lease expired <> resetting and the phone reboot. It happens to all IP phones in Building B. It also coincides with the DHCP renew of a computer over there. The computer handles the DHCP renew just fine.

We set the DHCP server to 4 days instead of every day. I know Linksys AP’s are one day by default but 4 days is perfectly fine for them. So now the resets only happen every 4 days.

Here are my ideas for fixing the problem but not sure if it will work. I have been on-site so much I just feel at this time I want to just leave things alone for a while.

- Change the DHCP server to another device.
- Change the AP’s bridge mode from Client Bridge to WDS Bridge. This I am told mimics a CAT5 Cable going across the two bridges. Maybe the phones are having trouble with how a Client Bridge mode because it works a little different.

I am wondering if anyone has ever run into this problem or similar and what might be a solution.

Kevin Kappenman
This is most likely a bug in the phone firmware. At 1/2 the lease time they should ask to renew the lease by directly asking the dhcp server. If they do not hear it asks again at some point I forget before the lease expires.

You need to see if it ask to renew the lease, you may have to place a sniffer in the path to see the messages or monitor your server.

I have see this behavior when the Ipphone was using LLDP to find the voice vlan but it would send the DHCP renews without the tag. The other thing to watch for is the original DHCP request is sent via broadcast but the renewal is sent by unicast.