Network Working Group P. Srisuresh Request for Comments: 3022 Jasmine Networks Obsoletes: 1631 K. Egevang Category: Informational Intel Corporation January 2001 Traditional IP Network Address Translator ( Traditional NAT) Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright ( C) The Internet Society (2001). All Rights Reserved. Preface The NAT operation described in this document extends address translation introduced in RFC 1631 and includes a new type of network address and TCP/ UDP port translation. In addition, this document corrects the Checksum adjustment algorithm published in RFC 1631 and attempts to discuss NAT operation and limitations in detail. Abstract Basic Network Address Translation or Basic NAT is a method by which IP addresses are mapped from one group to another, transparent to end users. Network Address Port Translation, or NAPT is a method by which many network addresses and their TCP/ UDP ( Transmission Control Protocol/ User Datagram Protocol) ports are translated into a single network address and its TCP/ UDP ports. Together, these two operations, referred to as traditional NAT, provide a mechanism to connect a realm with private addresses to an external realm with globally unique registered addresses. 1. Introduction The need for IP Address translation arises when a network s internal IP addresses cannot be used outside the network either for privacy reasons or because they are invalid for use outside the network. Network topology outside a local domain can change in many ways. Customers may change providers, company backbones may be reorganized, or providers may merge or split. Whenever external topology changes Srisuresh & Egevang Informational [ Page 1] RFC 3022 Traditional NAT January 2001 with time.
A NAT ( Network Address Translation or Network Address Translator) is the virtualization of Internet Protocol ( IP) addresses. NAT helps improve security and decrease the number of IP addresses an organization needs. Corporate E-mail Address: Please provide a Corporate E-mail Address. By submitting my Email address I confirm that I have read and accepted the Terms of Use and Declaration of Consent. By submitting your email address, you agree to receive emails regarding relevant topic offers from Tech Target and its partners. You can withdraw your consent at any time. Contact Tech Target at 275 Grove Street, Newton, MA. You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy. NAT gateways sit between two networks, the inside network and the outside network. Systems on the inside network are typically assigned IP addresses that cannot be routed to external networks (e.g., networks in the /8 block). A few externally valid IP addresses are assigned to the gateway. The gateway makes outbound traffic from an inside system appear to be coming from one of the valid external addresses. It takes incoming traffic aimed at a valid external address and sends it to the correct internal system. This helps ensure security, since each outgoing or incoming request must go through a translation process that also offers the opportunity to qualify or authenticate incoming streams and match them to outgoing requests, for example. NAT conserves the number of globally valid IP addresses a company needs, and in combination with Classless Inter- Domain Routing ( CIDR) has done a lot to extend the useful life of IPv4 as a result. NAT is described in general terms in IETF RFC 1631. The NAT mechanism ( natting ) is a router feature, and is often part of a corporate firewall.
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