Carrier-grade NAT

Another CGN scenario is Dual-Stack Lite, in which the carrier's network uses IPv6 and thus only two IPv4 addressing domains are needed.

This prompted some ISPs to develop a policy within the American Registry for Internet Numbers (ARIN) to allocate new private address space for CGNs, but ARIN deferred to the IETF before implementing the policy indicating that the matter was not a typical allocation issue but a reservation of addresses for technical purposes (per RFC 2860).

IETF published RFC 6598, detailing a shared address space for use in ISP CGN deployments that can handle the same network prefixes occurring both on inbound and outbound interfaces.

ARIN returned address space to the Internet Assigned Numbers Authority (IANA) for this allocation.

Allocating more private IPv4 address space for NAT devices might prolong the transition to IPv6.