POE Devices Not Working As Expected

[andrewburridge]

Hey Guys,

I have 10 new AIR-CAP3502I-A-K9 connected to a WS-C3750X-48PF-L switch.  8 of the APs power on and connect perfectly, but two are problematic.

Both devices are granted power, but they never go past the stage of getting power from the switch.  A look at POE shows:

Interface Admin  Oper       Power   Device              Class Max

                            (Watts)

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

Gi1/0/1   auto   on         15.4    AIR-CAP3502I-A-K9   3     30.0

Gi1/0/2   auto   on         15.4    AIR-CAP3502I-A-K9   3     30.0

Gi1/0/3   auto   on         15.4    AIR-CAP3502I-A-K9   3     30.0

Gi1/0/4   auto   on         15.4    Ieee PD             3     30.0

Where the AP that is not working is connected to Gi1/0/4.  The interface shows down/down.  I've tried shutting the interface, removing power, cdp etc.

Are there any other tricks you can think of to get it working or would you say that it's 2 faulty APs?  I am not based at site unfortunately so I cannot console to the APs and check them out.

Thanks for any help!

[Leo Laohoo]

Are there any other tricks you can think of to get it working or would you say that it's 2 faulty APs?  I am not based at site unfortunately so I cannot console to the APs and check them out.

Yes.  I've seen this issue very, very often.  I'm suspecting it's a cabling issue.  And there is a "trick" to find out.  Here are the command combination needed to be entered on the 3750X:

1.  Command:  test cable tdr interface Gi1/0/4;

2.  Wait for approximately 5 to 7 seconds;

3.  Command:  sh cable tdr interface Gi1/0/4; and

4.  Kindly post the output.

[andrewburridge]

Hey, thanks for your reply.  Output is as follows:

Interface Speed Local pair Pair length        Remote pair Pair status

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

Gi1/0/4   auto  Pair A     N/A                N/A         Normal

                Pair B     37   +/- 10 meters N/A         Open

                Pair C     37   +/- 10 meters N/A         Short

                Pair D     N/A                N/A         Normal

I take it this means that there's an issue with some of the pairs?  I'll get the cables swapped.  Thanks!

[Leo Laohoo]

I take it this means that there's an issue with some of the pairs?

Yes.  It means that the cable directly connected to the switch is faulty.

If you want to read a "lay man's" document about TDR, try this link here. 

Get the cables swapped and run the test again.  What you want to see under Pair Status are (for all four pairs) "NORMAL". 

[andrewburridge]

Hey man, thanks a lot for your help!

[Leo Laohoo]

Thanks for the ratings Andrew.  I presume the cable swap rectified the issue?