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ip phone causing 2950 port to errdisable

Hi

I have a customer running cme 3.0 with a number of IP phones connecting to a 2950 (standard). If they connect the phone to the switch before plugging in the power brick the switchport goes into an errdisable state requiring someone to shut/no shut the port. This causes problems when a user accidently unplugs their phone.

The switch is running Version 12.1(13)EA1. I didn't find anything bugtrack.

Here's a snippet of the port config

interface FastEthernet0/4

description ****PC/Phone Ports****

switchport mode trunk

switchport voice vlan 2

no ip address

mls qos trust device cisco-phone

spanning-tree portfast

I've tried it with trunking disabled on the port and the same thing occurs.

2 REPLIES
Anonymous
N/A

Re: ip phone causing 2950 port to errdisable

This is a normal behavior due to the telephone discovery algorithm. When an IP Phone is connected to a switch, the switch will send a signal to find out if the phone requires inline power or not and expect the signal to be looped back to itself. In order to for the IP Phone to loopback this signal, IP Phone is made to connect the pins when it's powered off. As a result, when the phone is connected to 2950, the keepalive from 2950 is looped back to itself, which will lead 2950 to detect loopback and errdisable the port. The solution is to configure " errdisable recovery "command in global mode and also to power on the phone before you connect it to 2950.

Anonymous
N/A

Re: ip phone causing 2950 port to errdisable

This is a normal behavior due to the telephone discovery algorithm. When an IP Phone is connected to a switch, the switch will send a signal to find out if the phone requires inline power or not and expect the signal to be looped back to itself. In order to for the IP Phone to loopback this signal, IP Phone is made to connect the pins when it's powered off. As a result, when the phone is connected to 2950, the keepalive from 2950 is looped back to itself, which will lead 2950 to detect loopback and errdisable the port. The solution is to configure " errdisable recovery "command in global mode and also to power on the phone before you connect it to 2950.

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