RogerBW's Blog

Wireless networks in the wild 05 July 2018

I've been running a wireless network receiver while out (mostly driving) with the smartphone, logging beacons and locations.

WiGLE WiFi FOSS does a decent job of this, and doesn't need to upload its data to the closed WiGLE database. You can export the data to a CSV file, but it's easier to copy the raw SQLite database elsewhere and work with that.

Of 17,760 distinct base station BSSIDs I've logged:

  • 2,923 are open
  • 117 offer WEP (kill it with fire)
  • 4,802 offer WPA1
  • 14,572 offer WPA2

(that totals more than the number of networks, since quite a few offer both WPA1 and WPA2)

  • 7,234 offer WPS (more than I expected since I rarely meet it; I suppose it's a thing that consumer-grade APs are more likely to have)

The vast majority of 2.4GHz networks are on the sensible channels of 1, 6 and 11 (3,500 or so on each, with about 100-200 on each of the others).

Of the network names with more than one AP, BTWifi (either BTWifi-X at 1,350 or BTWifi-with-FON at 1,144) are most common; then blank, Virgin Media, eduroam (I've been collecting in both Oxford and Cambridge), OWL (Oxford), and so on. Most Virgin (and Vodafone) networks have random numbers so that they don't appear with the same SSID.

Wycombe Abbey Lets has 58 APs scattered through the middle of town, which I can't help feeling must be treading on each other's toes.

Of the open networks, a distressing number seem to be HP printers: I ought to try connecting to one of these and seeing what it'll let me do without secondary authentication, though I hope not much.

A system like this, which logs latitude and longitude along with SSID, will obviously be confused by mobile APs. As well as the obvious stagecoach-wifi, berryscoaches-wifi and National Express Coach (all open networks, and on a previous occasion I've driven alongside a National Express coach while a passenger checked email) there are some suggestive names (numbers replaced by hashes, and all of these are WPA/WPA2):

  • Audi#####
  • Audi_MMI_####
  • BMW##### CarPlay
  • EE in car_WiFi_####
  • carswifi

and even one instance of

  • Skoda_WLAN_####

though I do want to give points for whoever came up with "house LANnister-5", somewhere in the northern reaches of Oxford.

  1. Posted by Owen Smith at 02:44pm on 05 July 2018

    6 and 11 are not sensible 2.4GHz wifi channels in the UK, we are supposed to use 1, 5, 9 and 13 which gives four non overlapping channels (though with no gaps in between). Base stations using 6 and 11 are either not configured for the UK or their software is not properly honouring the UK config setting.

  2. Posted by Owen Smith at 02:55pm on 05 July 2018

    I bought my dad a Samsung colour laser printer for christmas. It came with a wifi network and tap-to-print (Android compatible NFC) enabled by default, with no security that I could see. "Just connect to the network with your iOS device and print, and with Android just tap and it pairs automatically" it said in the instructions. The first thing I looked for are the config settings to turn off all wifi (two settings bizarrely, on for the network and one for "all wifi") and the NFC, then confirmed with wifi scanners that it is all off.

    iOS printing still works fine from my iPad since the printer is connected to my dad's network by ethernet cable (all of 0.5m long to the adjacent wifi base station) and my iPad is on his wifi.

    I don't understand why they feel the need to create a wifi network in the printer, surely the printer needs to join the house network to be useful? If it had an option to join the house wifi network and type in a password to join it I would understand, but I haven't found one yet (though I wouldn't use it given I have it cabled). The manual makes no mention of such an option.

  3. Posted by RogerBW at 03:16pm on 05 July 2018

    A four-channel (20MHz) separation is just about workable in a perfect lab environment but will cause bandwidth loss in the real world (especially where 802.11b is still in use, since that requires 22MHz, and will certainly be on the sensible channels); 25MHz separation is what the IEEE standard still specifies.

  4. Posted by Owen Smith at 02:21pm on 06 July 2018

    And the UK specifies that we should use channels 1, 5, 9 and 13. It may or may not make sense, but they are what we are supposed to be using. I forget now which specs say it. This is the entire reason we have channels 12 and 13, to give enough bandwidth for four non overlaping channels. Some parts of the world also have channel 14 but it is on a different frequency spacing so it doesn't overlap with anything.

    My 2.4GHz network is on channel 13. I can see about two dozen base stations from my house even downstairs, and they are liberally spread across most channel numbers from 1 to 11. The only pattern is almost half are on channel 1, after that it's a free for all. Channel 13 at least means I'm only overlapping with people on 10 and 11 and maybe a bit of 9 as you say.

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