Carrier-grade NAT (CGN or CGNAT), also known as large-scale NAT (LSN), is a type of network address translation (NAT) used by ISPs in IPv4 network design. With CGNAT, end sites, in particular residential networks, are configured with private network addresses that are translated to public IPv4 addresses by middlebox network address translator devices embedded in the network operator's network, permitting the sharing of small pools of public addresses among many end users. This essentially repeats the traditional customer-premise NAT function at the ISP level.
Carrier-grade NAT is often used for mitigating IPv4 address exhaustion.[1]
One use scenario of CGN has been labeled as NAT444,[2] because some customer connections to Internet services on the public Internet would pass through three different IPv4 addressing domains: the customer's own private network, the carrier's private network and the public Internet.
Another CGN scenario is Dual-Stack Lite, in which the carrier's network uses IPv6 and thus only two IPv4 addressing domains are needed.
CGNAT techniques were first used in 2000[citation needed] to accommodate the immediate need for large numbers of IPv4 addresses in General Packet Radio Service (GPRS) deployments of mobile networks. Estimated CGNAT deployments increased from 1,200 in 2014 to 3,400 in 2016, with 28.85% of the studied deployments appearing to be in mobile operator networks.[3]
- ^ S. Jiang; D. Guo; B. Carpenter (June 2011), An Incremental Carrier-Grade NAT (CGN) for IPv6 Transition, ISSN 2070-1721, RFC 6264
- ^ Chris Grundemann (2011-02-14). "NAT444 (CGN/LSN) and What it Breaks".
- ^ Livadariu, Ioana; Benson, Karyn; Elmokashfi, Ahmed; Dhamdhere, Amogh; Dainotti, Alberto (2018). Inferring Carrier-Grade NAT Deployment in the Wild (PDF). IEEE INFOCOM 2018 - IEEE Conference on Computer Communications. Honolulu, HI, USA. pp. 2249–2257. doi:10.1109/INFOCOM.2018.8486223. Retrieved 22 July 2021.