RFC 2694 (rfc2694) - Page 1 of 29

DNS extensions to Network Address Translators (DNS_ALG)

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Network Working Group                                       P. Srisuresh
Request for Comments: 2694                                    Consultant
Category: Informational                                      G. Tsirtsis
                                                         BT Laboratories
                                                             P. Akkiraju
                                                           Cisco Systems
                                                            A. Heffernan
                                                        Juniper Networks
                                                          September 1999


        DNS extensions to Network Address Translators (DNS_ALG)

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 (1999).  All Rights Reserved.

Abstract

   Domain Name Service (DNS) provides name to address mapping within a
   routing class (ex: IP). Network Address Translators (NATs) attempt to
   provide transparent routing between hosts in disparate address realms
   of the same routing class. Typically, NATs exist at the border of a
   stub domain, hiding private addresses from external addresses. This
   document identifies the need for DNS extensions to NATs and outlines
   how a DNS Application Level Gateway (DNS_ALG) can meet the need.
   DNS_ALG modifies payload transparently to alter address mapping of
   hosts as DNS packets cross one address realm into another. The
   document also illustrates the operation of DNS_ALG with specific
   examples.

1. Introduction

   Network Address Translators (NATs) are often used when 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.

   Ideally speaking, a host name uniquely identifies a host and its
   address is used to locate routes to the host. However, host name and
   address are often not distinguished and used interchangeably by
   applications. Applications embed IP address instead of host name in



Srisuresh, et al.            Informational
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