Friday, May 27, 2011

Cisco Wireless AP - LWAPP: How to Recover an AP from Mis-Configuration

I am quickly learning Cisco Wireless. I had a problem with a Cisco LWAPP AP located at a remote office. This AP had not previously registered with a Wireless LAN Controller (WLC). We rely on the DNS discovery method where the AP boots up and does a DNS lookup for CISCO-LWAPP-CONTROLLER or CISCO-CAPWAP-CONTROLLER.

Well this is were the fun began. IP address and name-server was manually configured in the AP, but the name-server IP address was fat-fingered. The APs will save their IP and LWAPP configuration automatically. On a reboot, the AP came up with the same configuration. I was finally able to restore the configuration to factory default and have it discover and join the controller.

To do this a console connection to the AP is required. I had a user at the remote office connect a console cable to a notebook and let me RDP in..

1) I need to clear the static IP address settings, convert to DHCP, and have the AP connect to the WLC. With LWAPP/CAPWAP APs, you can't just go into the config and change things.

"debug lwapp console cli" (if that doesn't work try "debug capwap console cli" )

This allows me to make changes to the running configuration, but these changes can not be saved to what us router-jockeys call "startup-config". The "magic" here is that when a LWAPP/CAPWAP access point connects to a WLC, it saves the controllers address in nvram. Thus when reboted, the AP always knows which WLC to try to connect to.

"interface f0"
"ip address dhcp"

I created a DHCP pool on the core switch and included the correct DNS server. In about 5 seconds, the AP obtained an IP address and the new DNS server. Then it registered with the controller

2) One problem. After rebooting, the Cisco Wireless AP came up with the old static IP addressing and DNS old/wrong DNS server. I was, however able to register with the controller because it had previously registered with that controller.

3) I logged into the Cisco Wireless Control System (WCS) and found the AP. I removed the Static IP setting and saved. The AP rebooted and registered, still had the wrong DNS server.

In WCS I went to Configure - Access Point and found the AP, scrolled to the bottom for "set to factory defaults", clicked "clear config".

Finally cleared it!

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