Cisco Dynamic Channel Assignment (DCA) Intervals

Some of you may already be aware of this pain point running WLC code 8.2 or later; this is when Cisco introduced the Flexible Radio Assignment (FRA) feature.

If you’re running the default Dynamic Channel Assignment (DCA) interval, which is 10 minutes, you really should change it to suit your wireless network – there are wireless clients that do not behave well (i.e. lose connectivity) when experiencing a channel change, you especially don’t want this with Voice over Wi-Fi.  However if you’ve never changed the update interval, or need to change it after upgrading to 8.2 code, you will run into a supposed issue trying to set the update interval longer than one hour.

The reasoning for this is easy to miss in the above link: “Set the FRA run interval (Valid Choices 1-24 hours must meet or exceed DCA interval)”, especially if you have never deployed any FRA-capable APs and don’t have FRA enabled.

If you try to set the DCA interval above 1 hour in the GUI or CLI you will get the following error:

(WLC-P001) >config advanced 802.11a channel dca interval 24

DCA Interval cannot be greater than FRA Interval.

You might go to double-check that FRA isn’t enabled, but you have to set the FRA interval to greater than the DCA interval:

(WLC-P001) >config advanced fra interval 24

(WLC-P001) >config advanced 802.11a channel dca interval 24

(WLC-P001) >config advanced 802.11b channel dca interval 24

I’ve not had a chance to play around with FRA on 2800 or 3800 APs yet, however the crew over at the No Strings Attached show have produced a white paper based on some testing, and the Borderless CCIE blog gives a good summary of what it is here.

If you want to debug WLC dynamic channel assignment updates you can use the following command: debug airewave-director channel enable

I hope this saves some people some headaches!

First_Post.bat

Welcome to my blog!

I’ve been playing with the idea of starting a blog for a while, as there are already so many amazing networking & wireless blogs out there (see my blog-roll-ception on the home page) I wanted to ensure I could provide some useful content of my own.

I’m sure you’re well aware that not all devices are the same in the world of networking, and especially wireless networking.  While I am not a Mac user, I am envious of some of the native capabilities in MacOS that provide some handy Wi-Fi tools, including some brilliant apps by Adrian Granados (check out AirTool).  I also like the fact you can view detailed Wi-Fi info from the menu bar.  This is handy when analysing client roaming behaviour and viewing the changes in signal strength and BSSID as a client associates to a new AP.

So that made me wonder if us Windows users could utilise something similar.  I came across a handy Netsh command: ‘netsh wlan show interface’

netsh

We see more information compared to the usual ‘ipconfig /all’; we can see BSSID, authentication method, radio type, cipher, channel, data rates and signal.  Now, the latter I have noticed not to be accurate and it is dependent on the Wi-Fi chipset and driver (this is my Surface Pro 2017).

So I was happy to discover this command, but wanted more.  There have been many scenarios where I’m testing roaming (in this instance verifying an 802.11r bug) walking around with a continuous ping, a multi-adapter packet capture, a WLC debug running… I want to easily refresh this ‘netsh’ command.

So here’s a little gift to you all, a bat file that refreshes the command at the hit of any key!

Download ‘netsh wlan.zip‘ (disclaimer: this file was free of viruses/malware when uploaded).

I hope you enjoyed my first post, feel free to leave a comment below and please follow as I will add more content!

EDIT: Update! I’ve purchased a 2015 MacBook Air and have been playing around with Adrian’s tools (Wi-Fi Explorer, AirTool, and Wi-Fi Check) as well as trying out some tools native to Linux such as nmap and sslcan for vulnerability analysis.  Great fun!