This patch adds support for RFC 6598 (Carrier Grade NAT) subnets (100.64.0.0/10) in libalias and ipfw.
In libalias, a new flag PKT_ALIAS_UNREGISTERED_RFC6598 is added. This is like PKT_ALIAS_UNREGISTERED_ONLY, but also is RFC 6598 aware.
Also, we add a new NAT option to ipfw called unreg_cgn, which is like unreg_only, but also is RFC 6598-aware.
The reason for the new flags/options is to avoid breaking existing networks, especially those which rely on RFC 6598 as an external address.
Submitted by: Neel Chauhan <neel AT neelc DOT org>