pfSense

Some ISPs are rolling out IPv6 and not directly providing a globally routable WAN address via DHCPv6. Instead, they are including a prefix delegation option that is used to exclude a prefix ID from being used internally, and using an address from that prefix ID for the WAN connection. This is documented in RFC 6603.

While there are ways to manually accomplish something similar using existing settings, such methods also require manual updating in the event that the prefix changes. As a result, external services relying on the WAN address (like VPN access) would be unavailable until such manual updating is done. Implementing this RFC would hopefully automate this process, eliminating some manual steps from being necessary in the event that the IPv6 prefix changes.

Obviously the prefix ID that is being excluded should also not be selectable for an internal network, and if someone has already configured a prefix ID that should be excluded (i.e. if the option changes in the future, or someone changes ISPs and the new ISP is excluding a network already configured), there should be some kind of notification of the conflict.