RFC 2671 (rfc2671) - Page 1 of 7


Extension Mechanisms for DNS (EDNS0)



Alternative Format: Original Text Document



Network Working Group                                            P. Vixie
Request for Comments: 2671                                            ISC
Category: Standards Track                                     August 1999


                  Extension Mechanisms for DNS (EDNS0)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

   The Domain Name System's wire protocol includes a number of fixed
   fields whose range has been or soon will be exhausted and does not
   allow clients to advertise their capabilities to servers.  This
   document describes backward compatible mechanisms for allowing the
   protocol to grow.

1 - Rationale and Scope

1.1. DNS (see [RFC 1035]) specifies a Message Format and within such
     messages there are standard formats for encoding options, errors,
     and name compression.  The maximum allowable size of a DNS Message
     is fixed.  Many of DNS's protocol limits are too small for uses
     which are or which are desired to become common.  There is no way
     for implementations to advertise their capabilities.

1.2. Existing clients will not know how to interpret the protocol
     extensions detailed here.  In practice, these clients will be
     upgraded when they have need of a new feature, and only new
     features will make use of the extensions.  We must however take
     account of client behaviour in the face of extra fields, and design
     a fallback scheme for interoperability with these clients.









Vixie                       Standards Track