Hanging out at my neighborhood coffee shop this evening and had some trouble getting online with their wifi. I could connect to the wifi but I wasn’t getting an IP address. I’ve found that it’s pretty common for coffee shops to have this problem; my theory is they aren’t making their DHCP lease times short enough, so throughout a day all the leases get used up but they aren’t released fast enough. I think a lease time of ten minutes would make sense for a public wifi hotspot; most routers default to something like one day. So after the 250-ish addresses in a usual /24 subnet have been assigned, the late folks are out of luck (this tech talk is hot, right?).

Another patron here with similar network geek tendencies was thinking along the same lines, so he went and checked the addresses that had been assigned to the folks who were already connected. Armed with that information we tried manually configuring our IP addresses in the same subnet and got ourselves online. I found it amusing that he and I both had public DNS addresses memorized, which we used to complete the settings.