Cisco 7921 / WLC / Cisco 1252 LWAPPS – Intermittent Wireless Voice Connectivity

I was working on a CUWN deployment in a healthcare environment with the following Charcteristics :

  • 7921 Phone Handsets
  • A Cisco 4404 Wireless Lan Controller running controller code
  • 1252 Light weight Access-points powered by 15.4W POE ports on a Catalyst 3750
  • Internal DHCP Server was being used.

The Site also had existing 1242 AP’s connected to the controller, however these where geographically seperate from the new deployment.

Everything was installed, configured and appeared to be running correctly, until after several days the 7921’s were having issues connecting. The following Symptoms were displayed:

  • The 7921 would display “DHCP TIMEOUT” on the screen and go into a loop
  • Not all of the AP’s would display the problem at the same time.
  • If you connected when associated with a functional AP and then roamed to a non-funtional AP network connectivity was extremly flaky.
  • The 1242 AP’s at the other end of the site were unaffected.

Once a 1252 was affected the only way to rectify the issue was to perform one of the following:

  • Perform a factory reset from the WCS by selecting “Clear AP Config”
  • Disabling and Re-enabling the WLAN.

It should be noted that merly rebooting the AP would not fix the issue.

OK, time to call TAC.

With TAC’s assistance I took the following action:

  1. Moved to an external DHCP server – This rectified the DHCP TIMEOUT Issue, however the poor connectivity continued
  2. I was using dot1x authentication with PEAP on the phones. – I moved to WPA/WPA2 with a Pre-shared Key for the voice WLAN. Didn’t fix the issue, however I was impressed with how much quicker association and Authentication took place.
  3. I upgraded the 4404 controller code to – This Appears to have Fixed the Issue.

Cisco IOS – Negating Terminal Commands

I always found it odd that I couldn’t negate terminal commands in IOS like other commands.

Eg;  no Terminal Monitor

I just assumed it wasn’t there, until I saw another engineer execute to disable term mon.

Router# terminal no monitor

It seems in IOS the terminal commands are special in that they require the terminal key word before the no keyword to negate sub-commands.

1252 LWAPP – Buzzing Access Point

I have been involved with a CUWN deployment using 1252 AP’s in a healthcare environment. Several of the Access-points were making buzzing noises whilst operating but for all intents and  purposes were functioning ok.

I knew these units probably needed to be replaced but I hadn’t had the time  to report the issue to TAC and get a replacement.

Well apparently I’m not alone. Jeremy at has mentioned the same issue showing up in a TAC Field notice. There is even a web tool for checking your serial numbers if they are affected.

The Field notice mentions issues with radio communication whilst buzzing, however I haven’t experienced these issues.

Thanks Jeremy!