IPng Working Group                                         Matt Crawford
Internet Draft                                                  Fermilab
                                                       February 26, 1999

                       IPv6 Node Information Queries

Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026. 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 and may be updated, replaced, or obsoleted by other documents
    at any time.  It is inappropriate to use Internet- Drafts as
    reference material or to cite them other than as "work in progress."

    To view the list Internet-Draft Shadow Directories, see

1.  Abstract

    This document describes an experimental protocol for asking an IPv6
    node to supply certain network information, such as its fully-
    qualified domain name.  IPv6 implementation experience has shown
    that direct queries for FQDN are useful, and a direct query
    mechanism for other information has been requested.

2.  Terminology

    A "Node Information (or NI) Query" message is sent by a "Querier"
    node to a "Responder" node in an ICMPv6 packet addressed to the
    "Queried Address."  The Responder sends a "Node Information Reply"
    to the Querier, containing information associated with the node at
    the Queries address.

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    document are to be interpreted as described in [2119].

    Packet fields marked "unused" must be zero on transmassion and

Expires September 3, 1999       Crawford                        [Page 1]

Internet Draft             ICMP Name Lookups           February 26, 1999

    ignored on reception.

3.  Node Information Messages

    Two types of Node Information messages, the NI Query and the NI
    Reply, are carried in ICMPv6 [2463] packets.  They have the same
    format, except that the Query lacks the Reply Data section.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |     Type      |     Code      |           Checksum            |
     |             Qtype             |             Flags             |
     |                                                               |
     +                             Nonce                             +
     |                                                               |
     |                                                               |
     /                          Reply Data                           /
     |                                                               |


    Type        TBA1 - NI Query.
                TBA2 - NI Reply.

    Code        For NI Query, always 0.
                For NI Reply:

                0   Indicates a successful reply.

                1   Indicates that the Responder refuses to supply the
                    answer.  The Reply Data field will be absent.

                2   Indicates that the Qtype of the Query is unknown to
                    the Responder.  The Reply Data field will be absent.

    Checksum    The ICMPv6 checksum.

    Qtype       A 16-bit field which designates the type if information
                requested in a Query or supplied in a Reply.  Its value
                in a Reply is always copied from the corresponding Query
                by the Responder.  Four values of Qtype are specified in
                this document.

Expires September 3, 1999       Crawford                        [Page 2]

Internet Draft             ICMP Name Lookups           February 26, 1999

    Flags       Qtype-specific flags which may be defined for certain
                Query types.  Flags not defined for a given Qtype must
                be zero on transmission and ignored on reception, and
                must not be copied from a Query to a Reply unless so
                specified in the definition of the Qtype.

    Nonce       An opaque 64-bit field to help avoid spoofing.  Its
                value in a Query is chosen by the Querier.  Its value in
                a Reply is always copied from the corresponding Request
                by the Responder.

    Reply Data  Qtype-specific data present only in an NI Reply message
                with ICMPv6 Type field equal to zero.  The length of the
                Reply Data may be inferred from the IPv6 header's
                Payload Length field [2460] and the length of the fixed
                portion of the NI Reply and the lengths of the ICMPv6
                header and intervening extension headers.

4.  Message Processing

    The Querier constructs an ICMP NI Query and sends it to the unicast
    address from which information is wanted.  The Nonce should be a
    random or good pseudo-random value to foil spoofed replies.  If true
    communication security is required, IPsec [2401] must be used.

    Upon receiving an NI Query, the Responder must check the Query's
    IPv6 destination address and discard the Query without further
    processing if it is not one of the Responder's unicast or anycast

    Next, if Qtype is unknown to the Responder, it must return an NI
    Reply with ICMPv6 Type = 2 and no Reply Data.  The Responder should
    rate-limit such replies as it would ICMPv6 error replies [2463,

    Next, the Responder should decide whether to refuse an answer, based
    on local policy not addressed in this document.  If an answer is
    refused, the Responder may send an NI Reply with ICMPv6 Type = 1 and
    no Reply Data.  Again, the Responder should rate-limit such replies
    as it would ICMPv6 error replies [2463, 2.4(f)].

    Finally, if the Qtype is known and the response is allowed by local
    policy, the Responder must fill in the Flags and Reply Data of the
    NI Reply in accordance with the definition of the Qtype and transmit
    the NI Reply with an ICMPv6 source address equal to the Queried
    Address, unless that address was an anycast address.  If the Queried

Expires September 3, 1999       Crawford                        [Page 3]

Internet Draft             ICMP Name Lookups           February 26, 1999

    Address was anycast, the source adderss for the Reply should be one
    belonging to the interface on which the Query was received.

    The Querier should silently discard any Reply whose Destination
    Address and Nonce do not match the Source Address and Nonce of an
    outstanding Query.

    An NI message of either sort must never be sent to a multicast

5.  Defined Qtypes

    The following four Qtypes are defined and must be supported by any
    implementation of this protocol.

    0   NOOP.

    1   Supported Qtypes.

    2   FQDN.

    2   Node Addresses.

5.1.  NOOP

    This Qtype has no defined flags and never has a Reply Data field.  A
    Reply to an NI NOOP Query tells the Querier that a node with the
    Queried Address was up and reachable, implments the Node Information
    protocol, and secondarily reveals whether the Queried Address was an
    anycast address.

5.2.  Supported Qtypes

    The Reply Data in an NI Supported Qtypes Reply is a bit-vector
    showing which Qtypes are supported by the Responder.  The Reply Data
    is grouped in complete 32-bit words, with the low-order bit in each
    word corresponding to the lowest numbered Qtype in a group of 32.  A
    1-valued bit indicates support for the corresponding Qtype.  The
    lowest-order four bits in the first 32-bit word must be set to 1,
    showing support for the four Qtypes defined in this specification.

    One flag bit is defined.

Expires September 3, 1999       Crawford                        [Page 4]

Internet Draft             ICMP Name Lookups           February 26, 1999

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |             Qtype             |          unused             |C|

    In a Query, a C-flag set to 1 indicates that the Querier will accept
    a compressed form of the Reply Data.  In a Reply, a C-flag set to 1
    indicates that the Reply Data is compressed.  The compression is not
    yet defined and may only be used in a Reply if the Query had the C-
    flag set.

5.3.  FQDN

    The NI FQDN Query requests the fully-qualified domain name
    corresponding to the Queried Address.  The Reply Data has the
    following format.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |                              TTL                              |
     |    NameLen    |                   FQDN ...                    |
     +-+-+-+-+-+-+-+-+                                               +
     /                                                               /
     +                                                               +
     |                                                               |

    TTL         The number of seconds that the name may be cached.  For
                compatibility with DNS [1035], this is a 32-bit signed,
                2's-complement number, which must not be negative.

    NameLen     The length in octets of the FQDN, as an 8-bit unsigned

    FQDN        The fully-qualified domain name of the Responder which
                corresponds to the Queried Address, as a sequence of
                NameLen US-ASCII octets, with periods between the
                labels, and no period after the last label.

    The Responder must fill in the TTL field of the Reply with a
    meaningful value if possible.  That value should be one of the

Expires September 3, 1999       Crawford                        [Page 5]

Internet Draft             ICMP Name Lookups           February 26, 1999

        The remaining lifetime of a DHCP lease on the Queried Address;

        The remaining Valid Lifetime of a prefix from which the Queried
        Address was derived through Stateless Autoconfiguration [2461,

        The TTL of an existing AAAA or A6 record which associates the
        Queried Address with the FQDN being returned.

    One Flag bit is defined, in the Reply only.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |             Qtype             |          unused             |T|

    A T-flag set to 1 in an NI FQDN Reply indicates that the TTL field
    contains a meaningful value.  If the T-flag is 0, the TTL should be
    set to zero by the Responder and must be ignored by the Querier.

    The information in an NI FQDN Reply with T-flag 1 may be cached and
    used for the period indicated by that TTL.  If a Reply has no TTL
    (T-flag 0), the information in that Reply must not be used more than
    once.  If the Query was sent by a DNS server on behalf of a DNS
    client, the result may be returned to that client as a DNS response
    with TTL zero.  However, if the server has the matching AAAA record,
    either in cache or in an authoritative zone, then the TTL of that
    record may be used as the missing TTL of the NI FQDN Reply and the
    information in the reply may be cached and used for that period.

    It would be an implementation choice for a server to perform a DNS
    query for the AAAA or A6 record that matches a received NI FQDN
    Reply.  This might be done to obtain a TTL to make the Reply
    cacheable or in anticipation of such a AAAA query from the client
    that caused the FQDN Query.

5.3.1.  Discussion

    Because a node can only answer a FQDN Request when it is up and
    reachable, it may be useful to create a proxy responder for a group
    of nodes, for example a subnet or a site.  Such a mechanism is not
    addressed here.

    IPsec can be applied to NI FQDN messages to achieve greater trust in
    the information obtained, but such a need may be obviated by
    applying IPsec directly to some other communication which is going

Expires September 3, 1999       Crawford                        [Page 6]

Internet Draft             ICMP Name Lookups           February 26, 1999

    on (or contemplated) between the Querier and Responder.  Node Addresses

    The NI Node Addresses Query requests some set of the Responder's
    unicast addresses.  The Reply Data is a sequence of 128-bit IPv6
    addresses, with Preferred addresses listed before Deprecated
    addresses [2461], but otherwise in no special order.  Four flag bits
    are defined in the Query, and five in the Reply.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |             Qtype             |       unused        |T|A|G|S|L|

    T   Defined in a Reply only, indicates that the set of addresses is
        inclomplete for space reasons.

    A   If set to 1, all the Responder's unicast addresses are
        requested.  If 0, only those addresses are requested which
        belong to the interface (or any one interface) which has the
        Queried Address.

    G   If set to 1, Global-scope addresses [2374] are requested.

    S   If set to 1, Site-local addresses [2374] are requested.

    L   If set to 1, Link-local addresses [2374] are requested.

    Flags A, G, S and L are copied from a Query to the corresponding

6.  IANA Considerations

    This document defines four values of Qtype, numbers 0 through 3.
    Following the policies outlined in [2434], new values, and their
    associated Flags and Reply Data, may be defined as follows.

         Qtypes 4 through 255, by IETF Consensus.

         Qtypes 256 through 1023, Specification Required.

         Qtypes 1024 through 4095, First Come First Served.

Expires September 3, 1999       Crawford                        [Page 7]

Internet Draft             ICMP Name Lookups           February 26, 1999

         Qtypes 4096 through 65535, Private Use.

    User of Private Use values should note that values above 8000 to
    9000 are likely to lead to fragmentation of "Supported Qtypes"

7.  Security Considerations

    The anti-spoofing Nonce does not give any protection from spoofers
    who can snoop the Query or the Reply.

    In a large Internet with relatively frequent renumbering, the
    maintenance of of KEY and SIG records [2065] in the zones used for
    address-to-name translations will be no easier than the maintenance
    of the NS, SOA and PTR records themselves, which already appears to
    be difficult in many cases.  The author expects, therefore, that
    address-to-name mappings, either through the original DNS mechanism
    or through this new mechanism, will generally be used as only a hint
    to find more trustworthy information using the returned name as an

8.  Acknowledgments

    This document is not the first proposal of a direct query mechanism
    for address-to-name translation.  The idea was discussed and
    deferred in the IPng working group and an experimental RFC [1788]
    describes such a mechanism for IPv4.

9.  References

    [1035] P. Mockapetris, "Domain Names - Implementation and
        Specification", RFC 1035, STD 13.

    [1788] W. Simpson, "ICMP Domain Name Messages", RFC 1788.

        Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels," RFC 2119.

    [2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
        Architecture", RFC 2373, July 1998.

    [2401] Kent, S. and R. Atkinson, "Security Architecture for the
        Internet Protocol", RFC 2401.

Expires September 3, 1999       Crawford                        [Page 8]

Internet Draft             ICMP Name Lookups           February 26, 1999

    [2434] Narten, T. and H. T. Alvestrand, "Guidelines for Writing an
        IANA Considerations Section in RFCs", RFC 2434.

    [2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
        for IP Version 6 (IPv6)", RFC 2461, December 1998.

    [2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
        Autoconfiguration", RFC 2462, December 1998.

    [2463] Conta, A. and S. Deering, "Internet Control Message Protocol
        (ICMPv6) for the Internet Protocol Version 6 (IPv6)
        Specification", RFC 2463, December 1998.

10.  Author's Address

    Matt Crawford
    Fermilab MS 368
    PO Box 500
    Batavia, IL 60510

    Phone: +1 630 840 3461

    Email: crawdad@fnal.gov

Expires September 3, 1999       Crawford                        [Page 9]