When talking of ``the resolver'', we do not mean any special
application, but rather refer to the resolver library, a
collection of functions that can be found in the standard C library. The
central routines are gethostbyname(2) and gethostbyaddr(2)
which look up all IP addresses belonging to a host, and vice versa.
They may be configured to simply look up the information in
hosts, query a number of name servers, or use the hosts
database of NIS (Network Information Service). Other applications, like
smail, may include different drivers for any of these, and need
special care.
