dose cisco IP phone can disable the pc port automatically

Unanswered Question
Jan 14th, 2009

hi guys

dose cisco IP phone can disable the pc port automatically when it detects a loopback on the phone.

for eg: if two cable from the back of the phones are plugged in to the switch.

Nortel phones can do that... not sure about cisco..


I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 2.5 (2 ratings)
Kenneth Mohammed Wed, 01/14/2009 - 17:52


I dont believe the PC port will be disabled automatically if the switch detects a bridging loop. I have had several customers to which this has happened, and we had to end up configuring port security on the switchports so that the port that detects the loop will go into error disabled mode.

Hope that helped, if so please rate.

Marwan ALshawi Wed, 01/14/2009 - 17:54

hi Kenneth

i was thinking about kind of port security

but whihc otion will be helpful in this case

is it max mac or what

thanks anyway

Kenneth Mohammed Wed, 01/14/2009 - 18:09

Off the top of my head, I believe we did something like the following:

switchport port-security maximum 2

switchport port-security

switchport port-security aging time 1


storm-control broadcast level 50.00

storm-control action trap

spanning-tree portfast

spanning-tree bpduguard enable

This seems to have remedied the issue. When the port detects a 3rd mac address, it goes into error disabled mode. However, beware, as things may break if you have users randomly moving computers and phones around by themselves. By the way, this was on some 3750 switches.

Hope that helped, if so please rate.

Nicholas Matthews Thu, 01/15/2009 - 05:36

The reason this happens is because having switches behind the phones is not supported - thus we have not programmed any switch-level protection into the phones.

Like kenneth mentioned, you would want to enable BPDU guard on phone ports to make sure you do not receive BPDU's. Likewise, configure the switch behind the phone not to send out BPDU's to the phones.




This Discussion