Traditional IP Network Address Translator (Traditional NAT)
RFC 3022
Document | Type |
RFC - Informational
(January 2001; Errata)
Obsoletes RFC 1631
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Authors | Kjeld Egevang , Pyda Srisuresh | ||
Last updated | 2013-03-02 | ||
Stream | Internet Engineering Task Force (IETF) | ||
Formats | plain text html pdf htmlized (tools) htmlized bibtex | ||
Stream | WG state | WG Document | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3022 (Informational) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
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, address assignment for nodes within the local domain must also change to reflect the external changes. Changes of this type can be hidden from users within the domain by centralizing changes to a single address translation router. Basic Address translation would (in many cases, except as noted in [NAT-TERM] and section 6 of this document) allow hosts in a private network to transparently access the external network and enable access to selective local hosts from the outside. Organizations with a network setup predominantly for internal use, with a need for occasional external access are good candidates for this scheme. Many Small Office, Home Office (SOHO) users and telecommuting employees have multiple Network nodes in their office, running TCP/UDP applications, but have a single IP address assigned to their remote access router by their service provider to access remote networks. This ever increasing community of remote access users would be benefited by NAPT, which would permit multiple nodes in a local network to simultaneously access remote networks using the single IP address assigned to their router. There are limitations to using the translation method. It is mandatory that all requests and responses pertaining to a session be routed via the same NAT router. One way to ascertain this would be to have NAT based on a border router that is unique to a stub domain, where all IP packets are either originated from the domain or destined to the domain. There are other ways to ensure this with multiple NAT devices. For example, a private domain could have two distinct exit points to different providers and the session flow from the hosts in a private network could traverse through whichever NAT device has the best metric for an external host. When one of the NAT routers fail, the other could route traffic for all the connections. There is however a caveat with this approach, in that, rerouted flows could fail at the time of switchover to the new NAT router. A way to overcome this potential problem is that the routers share the same NAT configuration and exchange state information to ensure a fail- safe backup for each other. Address translation is application independent and often accompanied by application specific gateways (ALGs) to perform payload monitoring and alterations. FTP is the most popular ALG resident on NAT devices. Applications requiring ALG intervention must not have their payload encoded, as doing that would effectively disables the ALG, unless the ALG has the key to decrypt the payload. This solution has the disadvantage of taking away the end-to-endShow full document text