Network hangs when IP phone is switched off

[ntk]

Hi,

I'm facing a peculiar problem. The network is working fine when the CCM and all the ip phones are functioning.

But if some identified phones are switched off, the entire LAN hangs and I'm not even able to login to the switch (3Com). During the problem if the phone is switched on again, then the network comes back to proper functioning..

CCM : 3.2(2c), Phone: Cisco 7910

Any inputs on the reason of this issue..

Regards,

ntk

[jchorlton]

I have seen this before on our 3Com switches.

Is STP enabled on the switch?

I think it is something to do with how a Cisco Switch identifies that a Cisco Phone is connected. Obviously a 3Com switch does not do that.

In our case enabling STP (not enabled by default on some older 3Com switches) sorted out the problem.

Someone explained the reason to me once, but I can't recall it - something to do with extended CDP?

John