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LWAPP disconnect from WLC for no reason



Scenario:-      Few of the LWAPP stop working properly (series of blinking red - green - amber)without any reason. All AP’s are plug on the same switch but only few of them are working fine. No configuration has been changed on the switch and only 4 AP’s are complaining.

For this particular scenario, few assumptions:-

Total AP in the network = 60

AP's unable to connect = 4

After enabling debugs LWAPP on these four AP, we get the error “could not discover any mwar". This error keeps coming up and blinking lights are noticed. The Blinking lights on AP’s indicate that they are not able to find the WLC.

Troubleshooting Steps performed without any Success:-

1. Reboot AP’s -- No success

2. Reset pushing the mode bottom at the same time connecting the Ethernet cord (POE) to the AP -- No success

3. Option 43 (DHCP) is setup correctly -- Checked

4. AP has a valid IP address -- Confirmed

5. AP is able to ping the WLC Management IP address -- Checked.


Step 1:-     We need to verify if the WLC reports only “X” number of access point supported.

For example in 4402 controller:-

In web management portion, check the Line located on the right hand side of the WLC picture that says “25 Access Points Supported” (please verify if your model 4402 supports 25 or 50 AP’s). So if you have 4402-25 regardless you will only ever get 25 to connect and not 50 AP’s.

Step 2:-     The normal function is one solid green and another blinking green light. Basically, two lights are showing green indicating represent normal functionality.

So how it works:-

1. In this Scenario, the WLC 4402-25 will not take more than 25 APs at a time.

2. When the AP’s discover the network, they discover the 4402-25, that returns the number of slots it supports (25), and the number of AP’s it already has.

3. The first 25 AP’s find that there is still space and join the controller.

4. All the other AP’s return an error message "cannot find a controller" (they find one, but it is not usable as such, as it has no available slot, so they say that they cannot find (a usable) controller.

5. These "stranded" access points keep rebooting and trying... forever.

6. Whenever one of the 25 first AP’s reboots / disconnects from the controller for any reason, some of the other access points may find that there is an available slot and join the controller.

7. The rebooting access point suddenly discovers that the slot is taken and returns "cannot find a controller".

There is no solution, except get some more controller slots, by sending the extra AP’s to another controller. This is an expected behavior if the controller only supports 25 AP’s or 50 AP’s.

Source:-      This document is generated from the following CSC thread.

For more information the DHCP option 43, video is available:-

Lightweight AP (LAP) Registration to a Wireless LAN Controller (WLC):-

Cisco 4400 Series Wireless LAN Controllers - Wireless LAN Controller (WLC) FAQ:-

Cisco 4400 Series Wireless LAN Controllers - Wireless LAN Controller (WLC) Design and Features FAQ:-

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