#! /usr/bin/perl
use strict;
use warnings;

my @nodes = qw(
db.blah.org
de.yahoo.com
mail.example.org
www.aol.com
www.example.org
www.freshmeat.net
www.hotdoggie.com.au
www.blah.org
);

# Schwartzian Transform
my @sorted =
  map { $_->[0] }
    # sort by domain
    sort { $a->[1] cmp $b->[1] }
      # "extract" domain.tld
      map { [ $_, join '.', (split m/\./)[-2,-1] ] }
        @nodes;


# check result
{
    local $, = local $\ = $/;
    print @sorted;
}