{
    foreach my $line
	(
	    # alias IPX off
	    "alias net-pf-4 off",
	    # alias IPV6 off
	    "alias net-pf-10 off",
	    "alias net-pf-47 ip_gre",
	)
    {
	unless (exists $lines{$line})
	{
	    push @lines, $line;
	}
    }
    foreach my $line
	(
	    "alias net-pf-15 ipsec",
	    "alias net-pf-50 ipsec",
	)
    {
	@lines = grep { !/^$line$/ } @lines;
    }

    "";
}
