Wireless Drivers Suck

For those of us who plan and maintain wireless networks you are well aware of the problems presented by how limited you are with 802.11b/g in the 2.4ghz band. One way that many network administrators attempt to work around this is to leverage 802.11a which is in the much more wide open and spacious 5ghz bands. A common way to configure the wireless network is to have dual radio access points that support both 802.11b/g and 802.11a and have both radios broadcast the same SSID for the convenience of your end-users.

I’m beginning to give up on the idea of using the same wireless SSID for both 802.11a and 802.11b/g radios. On all three platforms that I care about getting the wireless driver to prefer 802.11a over 802.11b/g is a waste of time. The vast majority of drivers for all three platforms seem to blindly check the SNR (Signal to Noise Ratio) of all visible APs advertising the desired SSID and ignore which band they are on. Because signals in 2.4ghz attenuate less than 5ghz signals this means 802.11b/g radios will always have the highest SNR and thus will always be preferred with a simple SNR check. This means the band you really want your users to use more is used the least.

On Windows you can manually configure some drivers to prefer 802.11a for the same SSID shared between 802.11a and 802.11b/g radios but it’s specific to the driver and many drivers do not even offer the option. And some drivers that do offer the option sometimes choose to ignore it for reasons unknown. (I’m looking at you Intel.) On Mac none of this is exposed in the UI and I’ve yet to even get Google to cough up a command line way of influencing what band and channel to pick.

On Linux it depends on if you choose to use NetworkManager and let the wireless driver select the channel itself. Depending on the driver quality you have the ability to specify the channel manually. To do this requires you to set it each time you wish to use wireless and this prevents roaming in many cases. It also turns what should be a two click and wait operation into something involving multiple manual commands and watching dmesg. It’s simply not a viable option for anyone except the network administrator himself.

So I’ve given up on that front and I’ve decided the best thing to do is to just offer an SSID that is only served from 802.11a radios. Within most of our buildings 802.11a signal should be sufficient for roaming so while it’s not a great solution its a usable one at least. So now we have the usual SSID that is advertised from all of our 802.11b/g and 802.11a AP radios and in addition to that we have an SSID labeled with “(802.11a)” thats only advertised from 802.11a radios. The Aruba gear we use makes it pretty trivial to have both SSIDs dump clients onto the same VLANs with the same AAA profiles so all it takes is about 5 lines of configuration to have no outside visible differences between the SSIDs.

I really wish there was a more auto-magical way to get clients to prefer 802.11a but I’ve yet to find a viable way to do it. So for now the SSID kludge will have to do.