Inflight wifi didn't work so of course I had to debug it. It appears the problem is lack of DHCP lease. The WiFi was using 8 hour leases, which was time enough for many planeloads of passengers to embark/disembark. A quick ARP scan at the time showed there were 55 devices on the network, almost entirely mobile devices (which randomize their MAC addresses, whereas laptops don't). Given the number of takeoffs and landings in the 8 hour period, the lease table can easily fill up. The fun fact about DHCP is that when this condition happens, it sends no response to the client. In other words, when trying to diagnose why " the wifi isn't working", there's no difference between this cause and half a dozen other causes. I have to guess this is the cause simply by looking at the fact lots of other people seem to have successfully gotten a DHCP response but I haven't. I told the flight attendant "the WiFi isn't working". She then "reset the Internet", after which I could get a lease. Apparently in the front near the entrance/exit, there's a button simply labeled "INTERNET RESET" that she presses whenever a customer complains. Obviously, one solution to the problem is that DHCP leases on planes should be drastically shorter, like at 1 hour intervals. Secondly, the number of leases should be drastically increased.