What will happen if I connect both IP Phone ports to a switch?

[jesnowakb]

Hi everyone!

This weekend I had a customer that called for an issue in his network. All their IP Phones started shuting down and registering again and again. After that the whole network was unstable. 

After hours of looking for the problem we found that there was an IP Phone that had both of their RJ-45 ports connected to the switch. After we disconneted the phone, everything went back to normal.

Can someone tell me why STP didnt block this port? How does the internal switch of the IP phone works? Does it eliminates BPDU packets (this is the only logical explianation I can come with)?

Thanks a lot! 

[saif musa]

Jesnowakb,

Personally, Im not thinging this issue is related to IP phone ports. Im using pc connecting to pc port on ip phone with wireshark installed on it. my point is, IF the ports are internal switch THEN i wouldnt be able to use wireshark with out any configuration on the pc port on ip phone to work as port mirror. the both ports works as one port. ( hub theory ), and thats why STP wouldnt block this port.

Regards

[jesnowakb]

Hi saif musa!

Thanks for your reply. 

Sorry I'm not clear with your explanation, so you thing this type of connection didn't cause the loop?

[Mark Malone]

is portfast not enabled on the switchport ? stp wont block it becasue ip phones dont send bpdu packets

in this instance this is why its recommended to always have bpduguard enabled with portfast to shut the port down , phones dont generate bpdus but they will pass them along the path