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How to Read Cable TDR Testing Result

PolarPanda
Beginner
Beginner

Hi network gurus, 

           I have a hard time to determine which part cable is broken at below. Do both short and open mean that we have cable issue from patch panel to the Ethernet port on the wall (the cable run inside the wall/ceiling), and the cable from switch port to patch panel is normal? Thank you. 

 

Swtich01#
Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi2/0/3  100M  Pair A     0    +/- 1  meters Pair A      Normal
                Pair B     0    +/- 1  meters Pair B      Normal
                Pair C     47   +/- 1  meters N/A         Short
                Pair D     49   +/- 1  meters N/A         Short

 

Switch 02#

Interface Speed Local pair Pair length        Remote pair Pair status

--------- ----- ---------- ------------------ ----------- --------------------

Gi1/0/20  10M   Pair A     0    +/- 1  meters Pair B      Normal

                Pair B     0    +/- 1  meters Pair A      Normal

                Pair C     22   +/- 1  meters N/A         Open

                Pair D     23   +/- 1  meters N/A         Open

2 Accepted Solutions

Accepted Solutions

Reza Sharifi
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Hi,

Have a look at this post. Leo published a good document on the TRD testing.

 

https://community.cisco.com/t5/networking-documents/how-to-use-time-domain-reflectometer-tdr/ta-p/3119327

 

HTH

View solution in original post

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend
Swtich01#
Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi2/0/3  100M  Pair A     0    +/- 1  meters Pair A      Normal
               Pair B     0    +/- 1  meters Pair B      Normal
               Pair C     47   +/- 1  meters N/A         Short
               Pair D     49   +/- 1  meters N/A         Short

The cable fault is located 47 or 49 metres away from the switch. 

Switch 02#

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/20  10M   Pair A     0    +/- 1  meters Pair B      Normal
                Pair B     0    +/- 1  meters Pair A      Normal
                Pair C     22   +/- 1  meters N/A         Open
                Pair D     23   +/- 1  meters N/A         Open

Cable fault is 23 metres away from the switch. 

NOTE:  

  • If the devices are only 10/100BaseTx then the result matches, i. e. Pairs C & D are "open". 
  • Starting with 3650/3850 (and newer), Cisco has "re-defined" the TDR functionality.  This feature will measure the distance of a BAD pair.  Good pair will "always" return with a distance of "0".  

 

View solution in original post

11 Replies 11

Reza Sharifi
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Hi,

Have a look at this post. Leo published a good document on the TRD testing.

 

https://community.cisco.com/t5/networking-documents/how-to-use-time-domain-reflectometer-tdr/ta-p/3119327

 

HTH

Deepak Kumar
Advocate
Advocate

Hi,

This will help you: https://community.cisco.com/t5/networking-documents/how-to-use-time-domain-reflectometer-tdr/ta-p/3119327

 

Regards,
Deepak Kumar,
Don't forget to vote and accept the solution if this comment will help you!

Martin L
VIP Advisor VIP Advisor
VIP Advisor

 

Do both short and open mean that we have cable issue?

- Not for 100 Mbps but Yes for 1000 Mbps.

based on my experience, this depends on speed and type of device at the end;  For 100Mpbs it is normal to have short/short if the IP camera is at the other end.  If you replace camera with a PC, short/short pairs would change into Open/Open.  so, Gi2/0/3 appears to have IP camera or IP phone installed at about 48 meters

In case of 10 Mbps, Open/Open is OK too. I don't think Pairs C, D are used on those 10M.

 

Regards, ML
**Please Rate All Helpful Responses **

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend
Swtich01#
Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi2/0/3  100M  Pair A     0    +/- 1  meters Pair A      Normal
               Pair B     0    +/- 1  meters Pair B      Normal
               Pair C     47   +/- 1  meters N/A         Short
               Pair D     49   +/- 1  meters N/A         Short

The cable fault is located 47 or 49 metres away from the switch. 

Switch 02#

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/20  10M   Pair A     0    +/- 1  meters Pair B      Normal
                Pair B     0    +/- 1  meters Pair A      Normal
                Pair C     22   +/- 1  meters N/A         Open
                Pair D     23   +/- 1  meters N/A         Open

Cable fault is 23 metres away from the switch. 

NOTE:  

  • If the devices are only 10/100BaseTx then the result matches, i. e. Pairs C & D are "open". 
  • Starting with 3650/3850 (and newer), Cisco has "re-defined" the TDR functionality.  This feature will measure the distance of a BAD pair.  Good pair will "always" return with a distance of "0".  

 

Hi Leo,

 

              THank you for the reply. Much appreciated. I looked at the article you wrote that the other two gurus mentioned in this post. I have a couple of follow up questions.

 

1. I don't understand this part. In my examples, the errors are C and D. Does it mean my cable issues relate to PoE and GigEtherent interface?

Pairs

Function

A

This pair controls whether or not the port should go up or down.

B

Protocol-level and controls FastEthernet.

C

Power over Ethernet (PoE)

D

GigabitEthernet

 

2. Basic on your article and reply, the broken cable should be either in horizontal line or Red. Am I correct? 

 

Thank you. 

Hi PolarPanda,

as i know it means that pair C is the cable pair used to bring PoE to devices, it should be the white/blue-blue cable pair. Pair D should be the white/brown-brown pair of the cable, without this pair all must work properly except 1Gbps speed, you can connect only at a max speed of 100Mbps.

Regards,

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend

The question I'd like to ask is this: Are the downstream clients capable of 1 Gbps or not.
I have seen a lot of wired clients that can only support 10/100BaseTx and the TDR will show exactly the same result of having Pair C & Pair D as "short" or "open".

Hi Leo,

What if you have a 100M device but pairs C and D are showing as short with pairs A and B are Normal?

--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/38  100M  Pair A     0    +/- 1  meters Pair B      Normal
                Pair B     0    +/- 1  meters Pair A      Normal
                Pair C     40   +/- 1  meters N/A         Short
                Pair D     39   +/- 1  meters N/A         Short
 

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend

What platform is this?  Is this a switch that runs on IOS-XE (3650/3850, IE3300/IE3400, Catalyst 9200/9300)? 

If it is, the result is not to be "trusted".   There is a TDR "bug" affecting switches running IOS-XE versions 16.X.X and 17.X.X.

The bug is the switch will provide incorrect output.  See examples below: 

(Above)  Pair A & B distance is "0".(Above)  Pair A & B distance is "0".

 


(Above)  Pair "A" distance is (significantly) more than Pairs B, C and D.(Above)  Pair "A" distance is (significantly) more than Pairs B, C and D.

 

  

This is a 9300 running IOS-XE 16.6.5. So we should not trust the test? My question is even if the endpoint is running at 100mb do we still look at pairs C and D? and if they are short we have a bad cable and they should be open? Or are pairs C and D not relevant at all since the device is running at 100mb? Thanks.

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend

@Ciscorocks wrote:
This is a 9300 running IOS-XE 16.6.5. So we should not trust the test?

I know I would NOT. 

100 Mbps only tests Pairs A & Pairs B and Pair D will always be "short". 

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