Access points goes down.

[Abhiblr]

I am frequently observing AP going down with reason stating: Radio reset due to (119) Max Retransmission.

AP Model: AIR-AP2802E.

May anyone please suggest what is causing the issue?

[balaji.bandi]

Give us more information about environment - WLC Version ? how frequenty happening ?  any issues you see over Etherenet connection side ?

Look at some tips :

https://mrncciew.com/2013/04/07/configuring-ap-retransmission-interval/

[Abhiblr]

WLC version: 5520.

AP:  AIR-AP2802E

I can see the issue quite often. Have verified the Ethernet side and everything looks fine except few MAC flaps that can be ignored in this scenario. Also, I dont see any packet loss on the WAN side.

Referring to the link, I can confirm that the WLC AP retransmit count is set to 5 and AP retransmit interval is set to 3 under Global configs.

[balaji.bandi]

 I dont see any packet loss on the WAN side.

is the WLC and AP resides different sites ?  not in the same LAN ?

[Abhiblr]

Yes. The WLC resides in a DC. AP is at another location.

[Scott Fella]

Is the problem tied to a single ap, single site, AP’s on the same switch?  Have you tried to swap out that ap to test?

[Abhiblr]

I have seen this issue with 4 AP's on same switch at same time. Cant swap AP for now.as they have live clients.

[Rich R]

what software version?

[Abhiblr]

Software Version 8.8.130.0

[Scott Fella]

I would recommend 8.10.x, but for now, do you think it's an issue with the switch, since you mentioned that all 4 are on the same switch?  You might want to test the cable and patch cable also and make sure that there is no dust and dirt on the ethernet port or the ap/switch/patch panel.  These can cause the ap's to drop here and there.  Verify that the switch has enough PoE for all the devices connected.

[Abhiblr]

Thanks Scott. Will check regarding the Layer 1 issue with Local IT team. However, power looks fine.

Gi1/0/18 auto on 26.0 AIR-AP2802E-E-K9 4 30.0
Gi1/0/19 auto on 26.0 AIR-AP2802E-E-K9 4 30.0
Gi1/0/20 auto on 26.0 AIR-AP2802E-E-K9 4 30.0
Gi1/0/21 auto on 26.0 AIR-AP2802E-E-K9 4 30.0

But just a doubt. If there is issue with cablings, there should be some errors on the Gig/e interface but its not in this case.

5 minute output rate 26000 bits/sec, 33 packets/sec
3454322 packets input, 821545881 bytes, 0 no buffer
Received 122601 broadcasts (100144 multicasts)
0 runts, 1 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 100144 multicast, 0 pause input

[Scott Fella]

Sometimes errors only show up on one side.  So depending if your switch supports the TDR command, you can use that so check the cable, but I would still have it tested and cleaned.  We had issues with ap's bouncing here and there and it was only solved when the tech used canned air to clean the ethernet port on the ap and switch along with the patch panel.  It really depends on how the ap's were installed and if the area was clean or in construction as an example.  Might not be your issue, but something to keep in mind.

[Abhiblr]

Note your point Scott. 

The TDR diagnostics shows "NORMAL"

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/20 1000M Pair A 83 +/- 10 meters Pair B Normal

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/18 1000M Pair A 58 +/- 10 meters Pair A Normal

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/13 1000M Pair A 52 +/- 10 meters Pair B Normal

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/19 1000M Pair A 58 +/- 10 meters Pair A Normal

[Scott Fella]

You should have pair A,B,C,D, not just one.  Here is a good reference from @Leo Laohoo 

How to use Time-Domain Reflectometer (TDR)

[Scott Fella]

Okay that looks fine.  Like I was mentioning previously, you should swap a good ap with a bad ap and see if the issue stays with the ap or not.  Helps to eliminate some variables that can point to the ap itself or maybe the cabling/switch.