Very Computer

Does anyone have some C source that can convert a dot-formatted IP address
into the original hostname?  Essentially, this should provide the same
functionality
as `nslookup` invoked in a similar manner.

TIA

--
Out of the 10Base-T, through the router, down the T1, over the
leased line, off the bridge, past the firewall... nothing but Net.

jeff

--

With a PC, I always felt limited by the software available.
                      On Unix, I am limited only by my knowledge.

 Paul> Does anyone have some C source that can convert a dot-formatted
 Paul> IP address into the original hostname?  Essentially, this
 Paul> should provide the same functionality as `nslookup` invoked in
 Paul> a similar manner.

The basic idea is to use inet_aton() to parse the numeric address,
then gethostbyaddr() to look up the host name.

There is one thing you should be cautious of, though: the person
controlling the reverse DNS for any given address can supply any hostname
he wants for that address, even hostnames that don't belong to him. If
you are using reverse-lookups in any security-relevent situation (which
includes any case where hostnames are being logged rather than raw IP
numbers), then you should verify that the claimed name does actually
belong to the specified IP number, by looking up the name with
gethostbyname() and checking that the original IP address appears
somewhere in the list of addresses for that hostname.

--
Andrew.