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The IP Network Address Translator (NAT) (RFC1631)

IP.com Disclosure Number: IPCOM000002467D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 9 page(s) / 21K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

K. Egevang: AUTHOR [+2]

Abstract

The two most compelling problems facing the IP Internet are IP address depletion and scaling in routing. Long-term and short-term solutions to these problems are being developed. The short-term solution is CIDR (Classless InterDomain Routing). The long-term solutions consist of various proposals for new internet protocols with larger addresses.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 14% of the total text.

Network Working Group K. Egevang

Request for Comments: 1631 Cray Communications

Category: Informational P. Francis

NTT

May 1994

The IP Network Address Translator (NAT)

Status of this Memo

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

Abstract

The two most compelling problems facing the IP Internet are IP

address depletion and scaling in routing. Long-term and short-term

solutions to these problems are being developed. The short-term

solution is CIDR (Classless InterDomain Routing). The long-term

solutions consist of various proposals for new internet protocols

with larger addresses.

It is possible that CIDR will not be adequate to maintain the IP

Internet until the long-term solutions are in place. This memo

proposes another short-term solution, address reuse, that complements

CIDR or even makes it unnecessary. The address reuse solution is to

place Network Address Translators (NAT) at the borders of stub

domains. Each NAT box has a table consisting of pairs of local IP

addresses and globally unique addresses. The IP addresses inside the

stub domain are not globally unique. They are reused in other

domains, thus solving the address depletion problem. The globally

unique IP addresses are assigned according to current CIDR address

allocation schemes. CIDR solves the scaling problem. The main

advantage of NAT is that it can be installed without changes to

routers or hosts. This memo presents a preliminary design for NAT,

and discusses its pros and cons.

Acknowledgments

This memo is based on a paper by Paul Francis (formerly Tsuchiya) and

Tony Eng, published in Computer Communication Review, January 1993.

Paul had the concept of address reuse from Van Jacobson.

Kjeld Borch Egevang edited the paper to produce this memo and

introduced adjustment of sequence-numbers for FTP. Thanks to Jacob

Michael Christensen for his comments on the idea and text (we thought

for a long time, we were the only ones who had had the idea).

1. Introduction

The two most compelling problems facing the IP Internet are IP

address depletion and scaling in routing. Long-term and short-term

solutions to these problems are being developed. The short-term

solution is CIDR (Classless InterDomain Routing) [2]. The long-term

solutions consist of various proposals for new internet protocols

with larger addresses.

Until the long-term solutions are ready an easy way to hold down the

demand for IP addresses is through address reuse. This solution takes

advantage of the fact that a very small percentage of hosts in a stub

domain are communicating outside of t...