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rfc:rfc1788

Network Working Group W. Simpson Request for Comments: 1788 Daydreamer Category: Experimental April 1995

                     ICMP Domain Name Messages

Status of this Memo

 This document defines an Experimental Protocol for the Internet
 community.  This does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

IESG Note:

 An Internet Engineering Steering Group comment from the co-Area
 Director for IPng:  Please note well that this memo is an individual
 product of the author.  It presents one view of the IN-ADDR
 mechanism, motivated by discussion in the IPNG WG of the difficulty
 of secure, dynamic update of the reverse tree.  Other IETF discussion
 and ongoing standards work on this area will be found in the IP Next
 Generation (ipngwg), DNS IXFR, Notification, and Dynamic Update
 (dnsind), DNS Security (dnssec) working groups.

Abstract

 This document specifies ICMP messages for learning the Fully
 Qualified Domain Name associated with an IP address.

Simpson [Page 1] RFC 1788 ICMP Domain Name April 1995

Table of Contents

   1.     Introduction ..........................................    2
      1.1       Direct Query ....................................    3
      1.2       Multicast .......................................    3
      1.3       Domain Names ....................................    3
      1.4       Messages ........................................    4
   2.     Domain Name Request ...................................    4
   3.     Domain Name Reply .....................................    5
   SECURITY CONSIDERATIONS ......................................    6
   REFERENCES ...................................................    6
   ACKNOWLEDGEMENTS .............................................    7
   AUTHOR'S ADDRESS .............................................    7

1. Introduction

 The Domain Name System (DNS) is described in [RFC-1034].  The IN-ADDR
 domain of the DNS is specified [RFC-1035] to perform address to
 domain name resolution, and to facilitate queries to locate all
 gateways (routers) on a particular network in the Internet.
 Neither function has been remarkably successful.  The IN-ADDR domain
 is not reliably populated.
 As multiple routers were used at boundaries and within networks, the
 IN-ADDR mechanism was found to be inadequate.  The location of
 routers by hosts is now performed using "ICMP Router Discovery
 Messages" [RFC-1256].
 As network numbers migrated to "classless" routing and aggregation,
 the IN-ADDR delegation granularity has fragmented, and requires
 overlapping administration.  The "reverse" IN-ADDR administration
 frequently does not follow the same delegation as the "forward"
 domain name tree.  This structure is not amenable to cooperative
 secure updating of the DNS.
 As application servers have appeared which require the Domain Name
 for user interaction and security logging, the IN-ADDR servers have
 been inundated with queries.  This produces long user visible pauses
 at the initiation of sessions.

Simpson [Page 2] RFC 1788 ICMP Domain Name April 1995

1.1. Direct Query

 This document proposes that each unicast address be queried directly
 for its corresponding Domain Name.  This has the advantages that the
 naming is under the same administration as the address assignment,
 and the queries are distributed in the same fashion as IP routing.
 In effect, the routing is used to index the database.

1.2. Multicast

 Only a few well-known multicast addresses are populated in the IN-
 ADDR domain.  The ephemeral nature of most multicast addresses is not
 conducive to cooperative secure updating of the DNS.
 However, the technique described here is not useful for multicast
 addresses.  A query to a multicast address could result in a storm of
 replies.  Most multicast groups are not named, or the member nodes
 are not configured with the name.
 The IN-ADDR method SHOULD continue to be used for reverse lookup of
 well-known multicast addresses in the range 224.0.0.0 to
 224.0.255.255.  Other multicast addresses are an issue for futher
 study.

1.3. Domain Names

 Each Domain Name is expressed as a sequence of labels.  Each label is
 represented as a one octet length field, followed by that number of
 octets.  Since every Domain Name ends with the null label of the
 root, a Domain Name is terminated by a length byte of zero.  The most
 significant two bits of every length octet must be '00', and the
 remaining six bits of the length field limit the label to 63 octets
 or less.
 When the most significant two bits of the length octet are '11', the
 length is interpreted as a 2 octet sequence, indicating an offset
 from the beginning of the message (Type field).  Further details are
 described in [RFC-1035] "Message Compression".
 To simplify implementations, the total length of a Domain Name
 (including label octets and label length octets) is restricted to 255
 octets or less.

Simpson [Page 3] RFC 1788 ICMP Domain Name April 1995

1.4. Messages

 The datagram format and basic facilities are already defined for ICMP
 [RFC-792].
 Up-to-date values of the ICMP Type field are specified in the most
 recent "Assigned Numbers" [RFC-1700].  This document concerns the
 following values:
     37  Domain Name Request
     38  Domain Name Reply

2. Domain Name Request

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |     Code      |          Checksum             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Identifier          |        Sequence Number        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type             37
 Code             0
 Checksum         The ICMP Checksum.
 Identifier       If Code is zero, a value to aid in matching requests
                  and replies.  For example, it might be used like a
                  port in TCP or UDP to identify a session.  May be
                  zero.
 Sequence Number  If Code is zero, a value to aid in matching requests
                  and replies.  For example, the number might be
                  incremented on each request sent.  May be zero.
 A separate Domain Name Request is used for each IP Destination
 queried.
 An ICMP Domain Name Request received with a broadcast or multicast
 Destination MUST be silently discarded.
 On receipt of an ICMP error message, the implementations MAY attempt
 to resolve the Domain Name using the IN-ADDR method.

Simpson [Page 4] RFC 1788 ICMP Domain Name April 1995

3. Domain Name Reply

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |     Code      |          Checksum             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Identifier          |        Sequence Number        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Time-To-Live                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Names ...
 +-+-+-+-+-+-+-+-
 Type             38
 Code             0
 Checksum         The ICMP Checksum.
 Identifier       Copied from the request.
 Sequence Number  Copied from the request.
 Time-To-Live     The number of seconds that the name may be cached.
                  For historic reasons, this value is a signed 2s-
                  complement number.
 Names            zero or more Fully Qualified Domain Names.  The
                  length of this field is determined from the total
                  length of the datagram.
                  When no names are known, the field is eliminated
                  (zero length), but the Reply is sent as an
                  authoritative indication that no name is known.
                  When more than one name is known, all such names
                  SHOULD be listed.
                  Any name which cannot entirely fit within the Reply
                  MTU is not sent.
 The IP Source in a Reply MUST be the same as the IP Destination of
 the corresponding Request message.
 Every host and router MUST implement an ICMP Domain Name server
 function that receives Domain Name Requests and sends corresponding
 Domain Name Replies.

Simpson [Page 5] RFC 1788 ICMP Domain Name April 1995

 A host SHOULD also implement an application- layer interface for
 sending a Domain Name Request and receiving a Domain Name Reply, for
 diagnostic purposes.

Security Considerations

 A primary purpose of this specification is to provide a mechanism for
 address to name resolution which is more secure than the IN-ADDR
 reverse tree.  This mechanism is amenable to use of the IP Security
 Protocols for authentication and privacy.
 Although the routing infrastructure to the Destination does not
 provide security in and of itself, it is as least as reliable as
 delivery of correspondence for the other sessions with the same peer.
 A DNS cryptographic signature, located by using the reply in the
 forward DNS direction, can be used to verify the reply itself.

References

 [RFC-792]
          Postel, J., "Internet Control Message Protocol", STD 5,
          RFC 792, USC/Information Sciences Institute, September
          1981.
 [RFC-1034]
          Mockapetris, P., "Domain Names - Concepts and Facilities",
          STD 13, RFC 1034, USC/Information Sciences Institute,
          November 1987.
 [RFC-1035]
          Mockapetris, P., "Domain Names - Implementation and
          Specification", STD 13, RFC 1035, USC/Information
          Sciences Institute, November 1987.
 [RFC-1256]
          Deering, S., Editor, "ICMP Router Discovery Messages",
          RFC 1256, Xerox PARC, September 1991.
 [RFC-1700]
          Reynolds, J., and J. Postel, "ASSIGNED NUMBERS", STD 2,
          RFC 1700, USC/Information Sciences Institute, October 1994.

Simpson [Page 6] RFC 1788 ICMP Domain Name April 1995

Acknowledgements

 The DNSIND and IPng Working Groups contributed substantial amounts of
 discussion.
 Additional comments should be submitted to the
 namedroppers@internic.net mailing list.

Author's Address

 Questions about this memo can also be directed to:
    William Allen Simpson
    Daydreamer
    Computer Systems Consulting Services
    1384 Fontaine
    Madison Heights, Michigan  48071
    Bill.Simpson@um.cc.umich.edu
        bsimpson@MorningStar.com

Simpson [Page 7]

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