Using a 3750 to test cables

The 3750 (and it would appear, the 3560s, 4500s, and 6500s) have an integrated Time Domain Reflector which is used to test cables associated with a port.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_see/command/reference/cli3.html#wp2168243

Today I was troubleshooting a problem at a newly renovated remote office with an IP phone that would power up but not boot. After swapping cables and phones, I remembered the TDR and tried it out:

Switch# test cable-diagnostics tdr interface g1/0/14
TDR test started on interface Gi1/0/14
A TDR test can take a few seconds to run on an interface
Use 'show cable-diagnostics tdr' to read the TDR results.
Switch#show cable-diagnostics tdr interface gigabitEthernet 1/0/14
TDR test last run on: March 04 22:31:09Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/14 auto Pair A 19 +/- 4 meters N/A Open
Pair B 4 +/- 4 meters N/A Open
Pair C 20 +/- 4 meters N/A Open
Pair D 20 +/- 4 meters N/A Open

Looks like a problem on Pair B! You should have heard the suprise from the (telecom) guy on the other end of the line when I finally said

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