Sniff Wi-Fi

If there's one recent change in the Wi-Fi world that has brought some heat and light to your humble blogger's cold, dark heart, it's the awareness of device differences.  But there's a difference between understanding that Wi-Fi devices have differences and creating an infrastructure that supports them.  And an important step in setting up a good Wi-Fi infrastructure is finding out whether the APs' transmit power is too high, too low or juuuuuuust right.  It has long been the recommended to have matching transmit power for devices engaging in two-way wireless communication, but with Wi-Fi that rule is often broken.  Breaking the rule is understandable because Wi-Fi environments are often vendor-neutral.  Most Wi-Fi deployments are not like the beaches of Normandy, where everyone had the same model of radio. Sometimes we need really, really good Wi-Fi, and matching the transmit power levels of APs and stations can go a long way towards fulfilling that need....

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There is a dirty little secret in the world of enterprise Wi-Fi: auto-channel selection doesn't work very well.  Every wireless LAN vendor has it.  Every wireless LAN vendor promotes it.  But when the Wi-Fi gets busy or crowded of full of mobile devices, auto channels will leave users frustrated and admins confused.   What to do about enterprise auto-channel?  Why, fix it, of course.  Here are some tips for getting it fixed the right way. First, the positive side of auto-channel: it saves you time.  Auto-channel selection is one of the two primary parts of auto-RF protocols that are supported by enterprise controllers, APs and management systems.  (The other part is auto-transmit power.)  Auto-RF protocols automatically adjust channel numbers and transmit power levels on APs.  Auto-RF protocols use information received by a large number of APs to decide when to adjust.  What that means is that if an AP senses a microwave oven b...

I have some interesting stuff about the topic that this blog is supposed to be about (WiFi sniffing) coming soon.  I promise.  But the FCC made some news concerning WiFi today, and I want to help people understand it. This post is happening because of what the FCC did in March, 2014.  What the FCC actually did was (probably) kill WiFi channels 52 to 144 by imposing new rules (the effects of which we have yet to see, because APs approved by the FCC prior to March, 2014 do not have to follow the new rules) that make WiFi devices more likely to work poorly when Doppler RADAR is on those channels.  What the FCC claimed they did was " increase availability of spectrum for high speed, high capacity " WiFi. Technically, the FCC can claim to be something other than liars.  The March, 2014 rules did increase spectrum availability in a narrow sample of use cases.  What was really going on, however, was the FCC doing the bidding of Doppler RADAR operators (who, ...

If there's one thing we've learned about WiFi over the years, it's that problems get fixed.  Site surveys used to be sooo annoying.  So we got controllers with auto-RF.  Guests used to complain and complain that we didn't have WiFi for them.  So we got captive portals.  And so the worl-- Wait a minute.  Auto-RF really doesn't work and we still need site surveys.  And captive portals annoy our friends in desktop support as much as they annoy our guests, plus they drag down overall WiFi performance.  Hmmm...  Let's start over: If there's one thing that we've learned about WiFi over the years, it's that sometimes what seems like a good solution to a problem only ends up making things worse.   Which brings us to our latest solution-that-only-makes-things-worse: Dual-radio APs with band-selectable radios. A little background: Last week, I was sitting in an office, minding my own business when I got a call.  A friend of mine wh...

Voice over WiFi is scary.  Retries, packet errors (due to lots of Retries) and high latency (usually due to packet errors that happen because of lots of Retries) will murder a WiFi network's ability to handle Voice and leave your users screaming (not actually screaming) like they were cast in a horror movie (or, at the very least annoyed like a character from Office Space).  But there's one thing that sometimes scares people, but really shouldn't: Voice Arbitration.  It's not going to kill your WiFi voice calls.  In fact, it will almost certainly help. Arbitration is a process defined in the 802.11 standard .  Every device (client/station and AP) goes through it. The simplest way I can describe 802.11 Arbitration is like so: If your AP or station has heard a quiet channel for 37 microseconds (0.000037 seconds), then your AP or station transmits a frame (what most people call a packet, but I call a frame). If your AP or station has been hearing a busy ch...

Nine months ago (bad way to start a blog post, I know) I wrote a blog about the future of WiFi sniffing .  In the comments section (perhaps the only worse thing for a blogger to say), someone mentioned a free, Windows-based application called Acrylic WiFi .   I briefly checked out the app and dismissed it as yet another Discovery utility disguised as a something more.  Then I actually used Acrylic WiFi and...  it works!  It sniffs WiFi frames (sort of) and it does it for free (outside of the cost of an ordinary 802.11 USB adapter)!  This changes everything (kind of)! For years, the method for free WiFi sniffing on a Mac has been simple.   Head down to the bottom of this post for a reminder. Now, we can do similar things in Windows.  It's not quite as simple and it's not totally free, but it works (pretty much). 1. Download and install  Acrylic WiFi Free , including Monitor Mode support (and, actually, if you can find an ol...