In the context of today's society, Carrier-grade NAT has become a relevant topic that deserves to be deepened and analyzed. From its origins to its impact today, Carrier-grade NAT has aroused the interest of experts and people from different fields. This article seeks to explore the various facets of Carrier-grade NAT, from its economic implications to its influence on popular culture. Along these lines, the different perspectives will be examined that will help us better understand the role that Carrier-grade NAT plays in our daily lives. Likewise, the controversies and debates that revolve around Carrier-grade NAT will be addressed, with the aim of enriching readers' knowledge and generating critical reflection on this topic.
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.
One use scenario of CGN has been labeled as NAT444, 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 1200 in 2014 to 3400 in 2016, with 28.85% of the studied deployments appearing to be in mobile operator networks.
If an ISP deploys a CGN, and uses RFC 1918 address space to number customer gateways, the risk of address collision, and therefore routing failures, arises when the customer network already uses an RFC 1918 address space.
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. The allocated address block is 100.64.0.0/10, i.e. IP addresses from 100.64.0.0 to 100.127.255.255.
Devices evaluating whether an IPv4 address is public must be updated to recognize the new address space. Allocating more private IPv4 address space for NAT devices might prolong the transition to IPv6.
Critics of carrier-grade NAT argue the following aspects: