JUNOS Built in Time Domain Reflectometer (TDR)
One handy feature that often goes overlooked and unused is the built-in TDR function in Juniper switches.
Here is a quick example on how to start the TDR test and then how to show the test results.
For comparison I have performed one on a cable that is jacked up against a known good cable between two EX2200-C's
##Set the cli timestamp so we get an idea of how long this takes
{master:0}
junspace@CDN1> set cli timestamp
Oct 03 10:49:04
CLI timestamp set to: %b %d %T
##Initiate the test
junspace@CDN1> request diagnostics tdr start interface ge-0/0/4
Oct 03 10:49:22
Interface TDR detail:
Test status : Test successfully executed ge-0/0/4
##Show the results
{master:0}
junspace@CDN1> show diagnostics tdr interface ge-0/0/4
Oct 03 10:49:43
Interface TDR detail:
Interface name : ge-0/0/4
Test status : Started
{master:0}
junspace@CDN1> show diagnostics tdr interface ge-0/0/4
Oct 03 10:49:50
Interface TDR detail:
Interface name : ge-0/0/4
Test status : Passed
Link status : Down
MDI pair : 1-2
Cable status : Open
Distance fault : 0 Meters
Polartiy swap : N/A
Skew time : N/A
MDI pair : 3-6
Cable status : Open
Distance fault : 0 Meters
Polartiy swap : N/A
Skew time : N/A
MDI pair : 4-5
Cable status : Open
Distance fault : 0 Meters
Polartiy swap : N/A
Skew time : N/A
MDI pair : 7-8
Cable status : Short on Pair-3
Distance fault : 0 Meters
Polartiy swap : N/A
Skew time : N/A
Channel pair : 1
Pair swap : N/A
Channel pair : 2
Pair swap : N/A
Downshift : N/A
##RESULTS: The test completed but we can see that there is a short on Pair3 and the other MDI Pairs are open. Now for a good cable to compare against
{master:0}
junspace@CDN1> request diagnostics tdr start interface ge-0/0/11
Oct 03 10:50:48
Interface TDR detail:
Test status : Test successfully executed ge-0/0/11
{master:0}
junspace@CDN1> show diagnostics tdr interface ge-0/0/11
Oct 03 10:51:00
Interface TDR detail:
Interface name : ge-0/0/11
Test status : Started
{master:0}
junspace@CDN1> show diagnostics tdr interface ge-0/0/11
Oct 03 10:51:09
Interface TDR detail:
Interface name : ge-0/0/11
Test status : Started
{master:0}
junspace@CDN1> show diagnostics tdr interface ge-0/0/11
Oct 03 10:51:14
Interface TDR detail:
Interface name : ge-0/0/11
Test status : Started
{master:0}
junspace@CDN1> show diagnostics tdr interface ge-0/0/11
Oct 03 10:51:19
Interface TDR detail:
Interface name : ge-0/0/11
Test status : Passed
Link status : UP
MDI pair : 1-2
Cable status : Normal
Distance fault : 0 Meters
Polartiy swap : Normal
Skew time : 0 ns
MDI pair : 3-6
Cable status : Normal
Distance fault : 0 Meters
Polartiy swap : Normal
Skew time : 8 ns
MDI pair : 4-5
Cable status : Normal
Distance fault : 0 Meters
Polartiy swap : Normal
Skew time : 0 ns
MDI pair : 7-8
Cable status : Normal
Distance fault : 0 Meters
Polartiy swap : Normal
Skew time : 0 ns
Channel pair : 1
Pair swap : MDI
Channel pair : 2
Pair swap : MDI
Downshift : No Downshift
## There we go all normal. TDR diagnostics is a good tool when you don't have a fluke around and you have an access cable that is acting up. Just give it a test.
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