INTERNET-DRAFT                            Mapping AS Number into the DNS
                                                               July 1997
                                                    Expires January 1998

     Mapping Autonomous Systems Number into the Domain Name System
     ------- ---------- ------- ------ ---- --- ------ ---- ------

                         Donald E. Eastlake 3rd

Status of This Document

   This draft, file name draft-ietf-dnssec-as-map-05.txt, is intended to
   be become a Best Current Practice RFC concerning utilization of the
   Domain Name System (DNS) to support routing security. Distribution of
   this document is unlimited. Comments should be sent to the DNS
   Security Working Group mailing list <> or to the

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months.  Internet-Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on (East USA), (West USA), (North Europe), (South Europe), (Pacific Rim), or (Africa).

Donald E. Eastlake 3rd                                          [Page 1]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS


   One requirement of secure routing is that independent routing
   entities, such as those identified by Internet Autonomous System
   Numbers, be able to authenticate messages to each other.  Additions
   have developed to the Domain Name System to enable it to be used for
   authenticated public key distribution [RFC 2065].  This draft maps
   all Autonomous System numbers into DNS Domain Names so that the DNS
   security can be used to distribute their public keys.

   [Changes from previous version are to accommodate AS numbers larger
   than 16 bits and to delegate on decimal boundaries rather than binary


   The contributions of the following persons, listed in alphabetic
   order, to this draft are gratefully acknowledged:

        Ran Atkinson

        Christian Huitema

        Tony Li

        Michael A. Patton.

Donald E. Eastlake 3rd                                          [Page 2]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

Table of Contents

      Status of This Document....................................1


      Table of Contents..........................................3

      1. Introduction............................................4

      2. Autonomous System Number Mapping........................5

      3. Meaning of RRs..........................................6

      4. Security Considerations.................................8
      Author's Address...........................................8
      Expiration and File Name...................................9

Donald E. Eastlake 3rd                                          [Page 3]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

1. Introduction

   There are a number of elements required to secure routing in the
   Internet.  One of these is a way that independently operated routing
   domains be able to authenticate messages to each other.

   Sharing a private symmetric key between each pair of such domains is
   impractical.  Assuming 2**16 Autonomous System routing entities,
   which is what is allowed in current versions of BGP, [RFC 1771], this
   would imply approximately 2**31 pairs, an impractical number of keys
   to securely generate, install, and periodically replace.

   The solution is to use public key technology whereby each routing
   domain has a private key it can use to sign messages.  Other domains
   that know the corresponding public key can then authenticate these
   messages.  Such authenticated messages can be used to set up and
   maintain efficient symmetric keys on an as needed basis.

   But how do the domains securely obtain the Autonomous System number
   to public key mapping?

   Extensions have been developed for the Domain Name System that enable
   it to be conveniently used for authenticated public key distribution
   [RFC 2065]. A variety of key types can be supported.  All that is
   required is a mapping of Autonomous System numbers into domain names,
   which is provided by this draft.

   It should be noted that the public keys retrieved from DNS will
   likely be used primarily to authenticate initial connection set up
   messages.  Autonomous Systems that need to converse with any
   frequency will probably negotiate more efficient symmetric session

Donald E. Eastlake 3rd                                          [Page 4]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

2. Autonomous System Number Mapping

   Autonomous System (AS) numbers are usually written as decimal number
   and when blocks of AS numbers are delegated to a registry, it is
   normally on decimal boundaries.  Their current use in BGP is limited
   to 16 bits providing a maximum value of 65,535.  For example, ANS is
   autonomous system 690.  However, there is no inherent size limit in
   the AS concept.  AS numbers are mapped into a domain name as
   described below.

   Write the AS number, as usual, as a decimal number without any
   "thousands" punctuation.  If it is less than 5 digits, add leading
   zeros to bring it up to five digits.  Then simply reverse the order
   of the digits, put a period between them, and append "" where "length" is the number of AS digits.  This mapping is
   analogous to the IPv4 address mapping into the DNS

   Thus the domain name correspond to Autonomous System 690 (decimal) is

   the domain corresponding to the largest possible AS number in BGP is

   the domain corresponding to AS number 65,000 is

   and the domain correspond to a hypothetical future greater than 16
   bit AS number 1,234,567 is

Donald E. Eastlake 3rd                                          [Page 5]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

3. Meaning of RRs

   The following guidance is given for some resource record (RR) types
   that could be stored under the names mapped from AS numbers.  The KEY
   RR is given first, followed by the SIG RR, the NXT RR, and then some
   additional RR types in alphabetic order.

        KEY: This type of RR associates a public key with the owner name
   which, in this case, corresponds to an Autonomous System (AS). Under
   DNS security as proposed in RFC 2065 the KEY RR can be used to store
   a variety of digital keys.  A KEY for use in securing routing
   communications between ASs will have the end entity flag bit on, the
   authentication use prohibited flag bit off, and a protocol byte or
   flag bit indicating routing communications use. Such a public key can
   be used to authenticate communications with or between ASs. The
   existence of such KEY RRs in the primary reason for mapping AS names
   into the DNS.

        SIG: The SIG signature resource record authenticates the RRs
   that it signs as described in RFC 2065.  Assuming the signer who
   generated the SIG is trustworthy, such as the zone owner,
   then the signed RRs can be trusted.

        NXT: An NXT RR is used in DNS security to provide authenticated
   denial of the existence of types and names as described in RFC 2065.

        A, AAAA: Type A or AAAA RRs SHOULD NOT be placed at AS nodes.
   AS domain names are reserved for Autonomous Systems only and should
   NOT be used for a host or any type of end entity other than an
   Autonomous System.

        CNAME: This type of RR is an alias pointing to another domain
   name.  An AS could have a CNAME pointing to a different AS but this
   is not likely to be very useful as AS RRs will normally be looked up
   when the AS number is actually encountered in use.

        MX: There is no special use for an MX RR for an AS name.  It
   could point to a host that would accept mail related to that AS.

        NS: The presence of NS records under an AS name means that it
   has been carved out as a subzone.  This gives the AS complete control
   over the zone refresh parameters and control over the creation of
   inferior names.  No special meaning is currently assigned to such
   inferior names so, although this is not advised, they could be used
   for hosts or whatever.  In this case, the will also be a zone KEY at
   the AS name, indicated by having the zone flag bit on.

        PTR: The part of the forward domain tree that administratively
   corresponds to the AS SHOULD be indicated by a PTR RR.  If some
   entity, say example.xx, has several ASs, there would be PTRs to

Donald E. Eastlake 3rd                                          [Page 6]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

   example.xx from several names in the hierarchy.

        RP: A Responsible Person RR SHOULD appear under each AS name
   telling you who you should contact in the case of problems with that

        TXT: Text RRs can be used for comments, postal address, or
   similar notes under an AS name.

Donald E. Eastlake 3rd                                          [Page 7]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

4. Security Considerations

   This document concerns a means to map Internet Autonomous System
   numbers into the Domain Name System (DNS) so that DNS can be used to
   provide secure distribution of Autonomous System's public keys.  The
   security of the resulting AS to key mapping is dependent on the
   security of the DNS security extensions and of the DNS zone where the
   key is stored.

   The most obvious way of using the AS keys retrieved from DNS is to
   authenticate communications with a directly connected AS.  However,
   this does not prove that any routing information exchanged is
   actually correct and note that routing information communicated over
   this secured path may be indirectly forwarded from or to yet other


   [RFC 1034] - Domain Names - Concepts and Facilities, P. Mockapetris,
   November 1987

   [RFC 1035] - Domain Names - Implementation and Specifications, P.
   Mockapetris, November 1987.

   [RFC 1771] - Y. Rekhter, T. Li, "A Border Gateway Protocol 4 (BGP-
   4)", 03/21/1995.

   [RFC 2065] - Domain Name System Security Extensions, D. Eastlake, C.
   Kaufman, January 1997.

Author's Address

   Donald E. Eastlake 3rd
   CyberCash, Inc.
   318 Acton Street
   Carlisle, MA 01741 USA

   Telephone:   +1 508 287 4877
                +1 703 620-4200 (main office, Reston, VA)
   FAX:         +1 508 371 7148

Donald E. Eastlake 3rd                                          [Page 8]

INTERNET-DRAFT                           Mapping AS Numbers into the DNS

Expiration and File Name

   This draft expires January 1998.

   Its file name is draft-ietf-dnssec-as-map-05.txt.

Donald E. Eastlake 3rd                                          [Page 9]