Fluke vs. Cisco VOIP: A Token Ring Story

Heres an interesting one. The other day I was called away from my desk with complaints of a phone continually trying to associate with the DHCP server. I had looked at this phone before, and my previous tactic was to unplug the client PC from the phone and then let the phone associate at which point I would plug back in the client PC. This time though it wasn’t so easy. The phone just wouldnt get an IP.

Luckily I had been tracing cables when I was called away, so I happened to have my trusty Fluke LinkRunner. This little baby has been my saviour manys a time accopanied with his buddy the Pro3000 Probe. I plugged the LinkRunner into the cable from the switch and lone behold it displayed the symbol for Token Ring…. Now I know there is some old stuff kicking around the building, but I dont even think they had Token Ring at all back in the day. So I traced the cable back on the switch and moved it over one port. Everything now worked fine, but being curious I decided to put the LinkRunner on the “Client PC” Cable.

And here is where the magic was happening. The apperant “Client PC” was actually another cable run to the switch . The phone had created its own little token ring network. From what I can gather, once the phone grabbed an address, it would pass through to give a DHCP address to the client PC… which happened to be the same switch the phone was plugged into, which caused the DHCP request to bounce around like a token.

Interesting behavior, and something that could have taken hours to track down without my trusty LinkRunner