Testing Copper Cables with Cisco Switches (TDR)

You can quickly detect any cable problems from your test with any 3560G/3750G/4500(with Gig Ports)/6500(with Gig Ports) by using the built-in IOS TDR. It will tell you the length of the cable and if there are any open pairs(and if so, where in the line they occur). This is better than running up to the location with a Fluke in hand to test cable problems.

First, you must run the test(its intrusive on the interface its being run on, so only run it on something that is OK to be unreachable for about a minute):

test cable-diagnostics tdr interface <InterfaceName>

After it completes, all you have to do is view the result:

show cable-diagnostics tdr interface <InterfaceName>

See the link below for the full scoop from Cisco:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_46_se/configuration/guide/swtrbl.html#wp1400280