> Pretty hard to do if people are using dialup. Or even dsl, unless they run a > linux box they don't ever reboot -- although I've found my dsl ip changing > sometimes on it's own, and with no rhyme or reason.
DSL lease timeout. A feature of DHCP-based dynamic IP addresses over permanent connections. Similar for cable, though the differences yo observed seem to be rather implementation-dependent than principial. > Cable is a little more stable, when I had a cable modem it didn't > change ip unless I shut off the modem for awhile, and not even always > then. Idea: What about a caller ID system, based on eg. SSL certificates or PGP signed challenge-response?