Quote from Zukaro
He's getting IP addresses confused with ports (I know what he put aren't IP addresses, but it's the only explination for him having to enter something different everytime he wants to allow friends to connect).
actually it has nothing to do with his ip. the way minecraft LAN is setup makes it so a random free port is chosen every time the game launches rendering the last port he opened on his router useless so he has to go and setup the new port displayed in the current open game.
and by all means am I not disregarding that DHCP does cause an ip change its just that unfortunately this is a function of the game itself so it is a bit harder to fix