Just for the record, I've been using the following little utility sub for handling IP addresses for a few years now.

sub ipto32bit {
#
# Convert a dotted quad c.d.e.f to a single unsigned 32bit number.
#
    my ($ip, $c, $d, $e, $f);
    $ip = shift;
    ($c,$d,$e,$f) = split(/\./,$ip);
    return ($c << 24) + ($d << 16) + ($e << 8) + $f;
}
[download]

Then it's just a matter of doing a straight lexical numerical sort. An example of how this might be used:

#!/usr/bin/perl -wl
use strict;

chomp(my @ips = <DATA>);

my @sorted_ips = sort by_ip(@ips);

print for (@sorted_ips);

sub by_ip {
    return ipto32bit($a) <=> ipto32bit($b);
}

sub ipto32bit {
#
# Convert a dotted quad c.d.e.f to a single unsigned 32bit number.
#
    my ($ip, $c, $d, $e, $f);
    $ip = shift;
    ($c,$d,$e,$f) = split(/\./,$ip);
    return ($c << 24) + ($d << 16) + ($e << 8) + $f;
}

__DATA__
12.345.111.3
12.345.111.26
61.8.47.111
12.345.111.24
203.134.35.27
12.345.111.5
12.345.111.4
[download]

Which gives:

12.345.111.3
12.345.111.4
12.345.111.5
12.345.111.24
12.345.111.26
61.8.47.111
203.134.35.27
[download]

Note that I started using the above before I learned about the inet_aton goodness that was pointed out by shmem above. So if I was looking for a solution now, shmem's is probably the one I would choose.

Cheers,
Darren :)