New Contributor

Interfering APs

Being very knew the the world of wireless, what harm does rogue interfering APs do to my brand new Aruba WLAN? I know the dangers of an unknown device, but I need to give my boss some facts about interference ie, the reason he should not consider putting that Netgear AP in a class room.
Aruba Employee

Re: Interfering APs

EDIT: A rogue AP means that someone has installed an AP on your network that you do not know about or control. The damage comes in a few potential forms, interference being one of them, but ARM can handle that. You will end up with a channel that ARM can't switch to due to interference on the channel. There will be some interference on that channel for any other nearby AP using that channel, as they will be competing for air time, possibly experiencing collisions, etc.

The bigger issue is security, if they have an open or easily compromised AP (WEP, bad PSK, etc.), you risk having an open port into your network accessible from the outside. Someone sitting in your parking lot now potentially has internal access to your network. Your boss probably doesn't want to be responsible for a security breach :)

Your Aruba WLAN will continue to function, and ARM will move away from the interference, but as you just bought a centralized WLAN you might want to go take out the random router installed on your network. What is it that he needs that AP to do that you can't provide with the WLAN?

Andy Logan, ACDX
Director, Strategic Account Solutions
Aruba Networks
New Contributor

Re: Interfering APs

Thanks for the reply, there is a teacher that has laptops that are not supported by our department as they are very old, so they are not in the domain. However the teacher wants to share a printer.

I personaly say that they should be gotten rid of, but it is hard to take away something once they have it. I have since convinced him to not put the rogue AP in do to the security risks you mentioned above.

I was simply triying to explain to him about interference and did not have the knowledge to convince him, as he said " I think you're blowing smoke up my ..."
Occasional Contributor II

Re: Interfering APs


If your system is 802.11b/g (2.4 GHz), you can tell him this :

In 802.11 b/g there are a total of 11 channels (assuming deployment in the United States). Of those 11 channels, ONLY 3 are not overlapping... in other words, only 3 are "clear channels". Those 3 channels are 1, 6 and 11.

So, let's assume that your system has 3 access points. The controller will assign each access point to a channel with the least amount of interference - meaning, the controller might assign one AP on channel 1, one AP on channel 6 and one AP on channel 11. Those are the 3 "clear channels".

Suddenly the teacher fires up his rouge access point, and it is on channel 4. That means that your APs on channel 1 and channel 6 are now experiencing interference. Where does the controller move them to avoid the interference ? No matter what the controller does, 2 of your APs are now experiencing interference.

The controller (via ARM) can attempt to mitigate that interference, but it does not eliminate it. Your teacher and his rouge access point has now caused degradation to your system.

Hope that helps.....

Occasional Contributor II

Re: Interfering APs

Interference is a factor, but not nearly as huge a factor as an managed hole in the network. A netgear wap sitting around in a room is an open invitation for me to get access to your network. First thought - are you *sure* that it's using WPA2 protection? Second, if I can get my hands on it I can reset it to factory and just plug in. Better yet, the MAC address is printed on the device so, if I can't get it through the netgear, I can tell your port security (which is probably MAB for this guy) that *I'm* the netgear.

I personally love to find these kinds of things around ^^
New Contributor

Re: Interfering APs

Thanks guys you have been a big help to this newbie of the air waves. :D
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