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I'm working with a couple Cisco WLCs and I know that they use information about client signal strength in determining device locations but I was reading up on "probe requests" and found that, by default, access points will forward probe requests they see only for SSIDs that they serve.

I found that I can disable the "filter" of probe requests so that APs will report all probe requests they see even if destined for unsupported SSIDs.

According to Cisco documentation they say that disabling "probe request filtering" will improve location accuracy but I can't tell if there are any caveats to doing so

Anyone have any experience with this?

The documentation I am going off of is here: http://www.cisco.com/en/US/docs/wireless/controller/7.4/configuration/guides/consolidated/b_cg74_CONSOLIDATED_chapter_01111010.html

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  • I have seen this enabled on a few client sites and it has never been part of any issue we were investigating. Nor can I see any reports of issues on the web. Guess its a nice additional feature to allow the algorithms to give more specific information. I assumed your Code level and there don't appear to be any bugs, cisco.com/en/US/docs/wireless/controller/release/notes/… .. but hey, you never know maybe in a heavily populate SSID arena you may encounter issues. – user255 May 8 '13 at 13:25
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From my own experience, there are no caveats in disabling the filters.

To be honest, if there were an alarming amount of probe data coming from unknown/unassociated SSIDs, I'd be more concerned about the rogue SSIDs popping up in the vicinity of your WLAN, and the interference they would cause, as a posed to the increase in probe data.

It will definitely increase accuracy on location, but don't expect it to magically turn a low density location deployment into a <5 meter accurate one. (although, I don't know the physics behind this yet, or the actual gains from doing this) If you're particularly worried, just keep an eye on the bandwidth of the tunnels going back to the controller. (unless you have a 3850 already)

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There is a trade off here. Yes, it will increase the accuracy of your location services. However it will increase the amount of "useless" data you gather as well (clients that are not part of your network), so you may need to consider the impact this has on your MSEs (i.e. if you are close to the MSE limitations already, you may have to look at adding additional MSEs or increasing the resources allocated to the VM).

Each environment is different, so it may be the increased accuracy is worth it no matter how much useless data you gather. It may be that so much useless information is gathered that the increased accuracy isn't a suitable trade-off.

If you are in an environment where there are a fair number of other wireless networks in operation or a fairly large wireless network with lots of clients, you will likely end up with significantly more "useless" data. A couple of examples where you might end up with a large amount of useless data would be if you are located in the middle of a number of high rise apartment buildings or right next to a university sports stadium.

However, the increased accuracy is really only achieved by capturing data from devices you are concerned with when they are NOT connected to your network. While Artanix brings up a great concern about rogue networks, I would be more concerned if devices I care about are connecting to other networks besides my own where my wireless network was operating.

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