This is not just ISA problem. It BIG upcoming IPv6 problem.
In many Linux distribs IPv6 is enabled by default. In spite of iptables can filter IPv6 usual admins don't care (don't know?) about it and filter only IPv4 traffic. So "filtered" with ipb4 deamons often availiable via IPv6.
You can find last discussion of this issues in recent Van Hauser speaks (http://www.google.com/search? q=Attacking+the+IPv6+Protocol+Suite) and toolkit (http://thc.org/thc-ipv6/) and some other articles, for example here: http://www.securitylab.ru/contest/264659.php (Russian).
Good compilation of IPv6 security links can be found here: http://www.seanconvery.com/ipv6.html
