[Fixed] UC500 reboot - will no longer give out dhcp to phones

Unanswered Question
Aug 29th, 2010

Hi All

Very weird problem here,

My UC500 unit powered off (loss of power), when it came back up none of my ip phones are able to get ip, config or register properly.

I tried resoring my config (in case config was wrong), but that didn't help and in the end I restored to factory default - but that didn't help either.

It will allocate IPs to the data pool (which I have since removed as my windows server does this on our network) but the phones cannot get an IP, so they never request tftp settings and thus never register.

I've unplugged everytnig from unit except a couple of phones.

Thanks in advance


After experimenting with stopping the cdp and vlans on the built-in ports. I discovered that during a test where I restored one of the fast ethernet ports to normal service with this command:

switchport voice vlan 100

the system reported "Vlan 100 does not exist, creating it" (or something like that anyway) and viola! Everything started working properly!

I have no idea what caused the issue - I'm just glad its working now!

If I can just get my 7970's out of their factory reset loops (looks like they are trying to upgrade to new loads, but are failing) - I'll be back to normal and a very happy chappy!

I have this problem too.
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anthonyfear Mon, 08/30/2010 - 02:57

Some more information on this issue:

I manually setup one of my phones with a static IP addres, and configured the tftp server etc.

Even after that, the phone is not reachable (i.e. it cannot be pinged), and the tftp request never reaches the uc500 (I did a debug of tftp).

This makes me think the issue is possibly vlan related? is it posible the voice vlan is not working? How I debug that?

Phones says vlan is 100, uc500 is configured for voice on 100 (everything is at factory defaults)- it's so weird!

Felipe Garrido Mon, 08/30/2010 - 07:21

Can you attach the current running configuration. Also, is the IP phone connected directly to the UC5x0 or via an external switch?


anthonyfear Mon, 08/30/2010 - 07:29

Hi There

All phones are attached directly to uc500!

Running config attached below (I didn't remove anything as it's only running factory default configuration and it's not attached directly to internet)

In fact I have made some progress - on one of the ports I used these commands :

no cdp enable


no switchport voice vlan 100 - the phones will pickup IPs and register!

Any idea why the vlan 100 might be causing a problem?


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