use Socket qw( inet_aton AF_INET);

my $addr = '209.197.123.153';

my ($name) = gethostbyaddr(inet_aton($addr), AF_INET)
   or do { die "No name for addr $addr\n" if $!==0;
           die "gethostbyaddr: $!\n";
         };

print("$name\n");  # perlmonks.pair.com