Carrier-grade NAT

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Carrier-grade NAT

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.

Contents

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 1200 in 2014 to 3400 in 2016, with 28.85% of the studied deployments appearing to be in mobile operator networks. [3]

Shared address space

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. [4] The allocated address block is 100.64.0.0/10, i.e. IP addresses from 100.64.0.0 to 100.127.255.255. [5]

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.

Advantages

Disadvantages

Critics of carrier-grade NAT argue the following aspects:

See also

Related Research Articles

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In order to ensure proper working of carrier-grade NAT (CGN), and, by doing so, alleviating the demand for the last remaining IPv4 addresses, a /10 size IPv4 address block was assigned by Internet Assigned Numbers Authority (IANA) to be used as shared address space. This block of addresses is specifically meant to be used by Internet service providers that implement carrier-grade NAT, to connect their customer-premises equipment (CPE) to their core routers.

References

  1. ↑ S. Jiang; D. Guo; B. Carpenter (June 2011), An Incremental Carrier-Grade NAT (CGN) for IPv6 Transition, ISSN   2070-1721, RFC   6264
  2. ↑ Chris Grundemann (2011-02-14). "NAT444 (CGN/LSN) and What it Breaks".
  3. ↑ 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.
  4. ↑ "Re: shared address space... a reality!". Archived from the original on 2012-06-07. Retrieved 13 September 2012.
  5. ↑ Chris Grundemann (2012-03-13). "100.64.0.0/10 – Shared Transition Space".
  6. ↑ RFC   7021 - Assessing the Impact of Carrier-Grade NAT on Network Applications
  7. 1 2 "MC/159 Report on the Implications of Carrier Grade Network Address Translators Final Report". Ofcom. 2013-04-15. Retrieved 2023-10-17.
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