use HTML::LinkExtor;
use URI;

my @links = ();
my $html = do { local $/; <DATA> };

sub extract_links {
    my ($tag, %attr) = @_;
    next unless $tag eq 'a';
    my @parts = split /\./, URI->new($attr{href})->host;
    my $host = join '.', @parts[-2, -1];
    push @links, $host;
}

my $p = HTML::LinkExtor->new(\&extract_links);
$p->parse($html);

print join "\n", @links;

__DATA__
<a href="http://www.foo.com">description</a>
<a href='http://www.foo.com'>image here</a>