Cable TDR Testing

snarayanaraju · ‎12-16-2014

Hello All - I am working on Cable TDR Testing. I am seeing on the result "FAIL" on couple of Pairs (C & D). What does FAIL indicates.

However the end devices are working perfectly alright. But manytimes this FAIL message misdirecting my Operation Engineers while troubleshooting.

I am seeing this messgae wide across my environment.

ST1912#show cable-diagnostics tdr interface gig 1/0/12
Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/12 100M Pair A     36   +/- 4 meters Pair B      Normal
                Pair B     57   +/- 4 meters Pair A      Normal
                Pair C     109 +/- 4 meters Pair C      Fail
                Pair D     102 +/- 4 meters Pair D      Fail

ST1924##show cable-diagnostics tdr interface gigabitEthernet 1/0/8
Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/8   10M   Pair A     49   +/- 4 meters Pair A      Fail
                Pair B     49   +/- 4 meters Pair B      Fail
                Pair C     150 +/- 4 meters Pair C      Normal
                Pair D     104 +/- 4 meters Pair D      Fail

3750 Configuration Guide do have only these below details about the Pair Status

Pair status

The status of the pair of wires on which TDR is running:

Normal   —The pair of wires is properly connected.
Not completed   —The test is running and is not completed.
Not supported   —The interface does not support TDR.
Open   —The pair of wires is open.
Shorted   —The pair of wires is shorted.
ImpedanceMis   —The impedance is mismatched.
Short/Impedance Mismatched  —The impedance mismatched or the cable is short.
InProgress    —The diagnostic test is in progress

Thanks in advance

regards,

SAIRAM

Leo Laohoo · ‎12-16-2014

What does FAIL indicates.

The TDR result of FAIL, SHORT, IMPEDANCE MISMATCH are all pointing to a bad cable (either patch cable or horizontal cable).

Personally, I would never accept a TDR with a result other than NORMAL (when connected to a NIC).

Leo Laohoo · ‎12-16-2014

What model of switch are you running the TDR?

What IOS is this running?

Look at the result. Don't just look at the last column. Look at the estimated distance. All I can say is WTF. If it's true that the some of the pairs are indeed >100 metres then there are only two possibilities:

1. The horizontal cabling is so atrocious or degraded that it's causing a mis-reading of the TDR result;

2. There's a possibility of a consolidation point and it's not terminated properly; or

3. The IOS running on the appliance could be buggy.

snarayanaraju · ‎12-16-2014

IOS: 12.2(55)SE3 C3750-IPBASEK9-M

MODEL: Cisco 3750-X

Leo Laohoo · ‎12-16-2014

IOS: 12.2(55)SE3

This is a stable train but not fully matured IOS version. You may want to consider 12.2(55)SE9.

MODEL: Cisco 3750-X

With the right IOS, the TDR function of a 3750G/E/X is more accurate.

snarayanaraju · ‎12-17-2014

Thank you Sir. Much appreciated your response