Cisco – Cable Testing (TDR – Time Domain Reflectometer)

NOTE :

– Only works with 10/100/1000 copper
– SFP and copper 10/100 not supported

Command CLI :

agink_sw# test cable-diagnostics tdr interface <port interface>
agink_sw# 
agink_sw# 
agink_sw# show cable-diagnostics tdr interface <port interface>
agink_sw# 
agink_sw#

Example :

agink_sw# test cable-diagnostics tdr interface gigabitEthernet 1/0/1
agink_sw#
agink_sw#
agink_sw# show cable-diagnostics tdr interface gigabitEthernet 1/0/1
TDR test last run on: Feb 13 10:13:59

Interface    Speed     Local pair      Pair length                Remote pair    	Pair status
---------    -----     ----------      ------------------         -----------           --------------------
Gi1/0/1      auto      Pair A          28   +/- 1  meters         N/A                    Open
                       Pair B          27   +/- 1  meters         N/A                    Short/Crosstalk
                       Pair C          27   +/- 1  meters         N/A                    Short/Crosstalk
                       Pair D          28   +/- 1  meters         N/A                    Open

Pairs A & B = typical receive/transmit
Pair C = PoE
Pair D = GigabitEthernet

NOTE :
On 100Mb cables, you will probably see the status “Short” on Pairs C & D. This is normal.

Under “Pair status” you can get the following results:

Result

Explaination

Normal Ideal result you want.

  • If testing FastEthernet, you want Pair A and B as “Normal”.
  • If testing GigabitEthernet, you want ALL as “Normal”.
Open Open circuit. This means that one (or more) pair has “no pin contact”.
Short Short circuit.
Impedance Mismatched Bad cable. For more explanation, go here.