Wireless wanderings

APs in monitoring mode

So I just made a comment on an old post of George Stefanick’s extremely useful blog regarding Cisco APs set to Monitoring mode. I also realised that considering there are only 2 posts here one should attempt to populate my own blog with a bit of text. Have a read of George’s post and my response at the above link or you can get the jist from my reply below. FYI the ratio I mention is Monitoring vs Client serving APs.

I’m dredging this one up from the past a bit but it is a particular topic I was wondering about recently.

When I first heard of this function I originally thought a 1:4 ratio would be the best design on a basic level if you were being ‘frugal’ with your AP density and to provide 1 AP per channel in the 2.4Ghz range with another to monitor those channels constantly. As this was probably more applicable when you wrote this post over two years ago, how did you come to the 1:6 conclusion and have your views on this changed due to the drop in price of APs and higher density designs being more in demand. Those two factors might actually produce opposing designs!

I’ve learnt from your post that the monitoring APs are constant versus the occasional reporting from LW APs (thanks for that tidbit), but with Cisco saying …

“Although in many cases the best response to interference is for the administrator to manually move, remove, replace, or shield the interfering device, automated mitigation is highly desirable to maintain short-term performance until other actions can be taken.”

… Can the price of Monitoring APs be really justified if they can’t service clients at all? Now my mind is going down the path of temporary monitoring when heavy congestion is reported either by converting an existing AP in the area or temporarily installing an AP earmarked for such a use. Would require more active onsite IT staff however!

I had endless questions popping up in my head as I wrote that response but managed to hold most of the crazy in for here. If I were a customer receiving a recommendation to place these Monitoring APs in regardless of ratio (Monitoring APs vs Local mode APs) I would immediately be thinking:

  • Can clients connect to Monitoring APs – I already no the answer to that is no.
  • How important is continuous monitoring?
  • Do I have enough non-WiFi interference to require 24×7 monitoring?
  • Can there be an automated setup where only one AP is in monitor mode per day but it changes cluster / area every 24 hours so monitoring is continuous but never in more than one area? In that case I’d have them swap at 2AM or so to avoid any clients being interrupted but it could provide definitive RRM measurements without
  • If I do want more in depth monitoring of rogues, I guess I’ll have to spend more money on MSE too..

So many questions and fortunately so much time! I’m not sure if I will get round to answering those straight away on here but it has helped me sift through a few angles.

In my opinion it is always good to try and look at these things from the customer’s perspective because at the end of the day you want them to receive the most efficient and cost-effective design with as little bullshit as possible.


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