Each computer on the Internet has one or more Internet addresses,
numbers which identify that computer among all those on the Internet.
Users typically write IPv4 numeric host addresses as sequences of four
numbers, separated by periods, as in `126.96.36.199', and IPv6
numeric host addresses as sequences of up to eight numbers separated by
colons, as in `5f03:1200:836f:c100::1'.
Each computer also has one or more host names, which are strings
of words separated by periods, as in `mescaline.gnu.org'.
Programs that let the user specify a host typically accept both numeric
addresses and host names. To open a connection a program needs a
numeric address, and so must convert a host name to the numeric address
it stands for.