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IPng Working Group                                         Matt Crawford
Internet Draft                                                  Fermilab
                                                         August 28, 2000

                       IPv6 Node Information Queries
                <draft-ietf-ipngwg-icmp-name-lookups-07.txt>



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
    http://www.ietf.org/shadow.html.


Abstract

    This document describes a 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 a DNS name are useful, and a direct query mechanism for other
    information has been requested.


1.  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 Query concerns a "Subject Address" which may
    differ from the Queried Address, or a "Subject Name".  The Responder
    sends a "Node Information Reply" to the Querier, containing
    information associated with the node at the Queries address.  A node
    receiving a NI Query will be termed a Responder even if it does not
    send a Reply.

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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    document are to be interpreted as described in [2119].

    Packet fields marked "unused" must be zero on transmission and,
    aside from inclusion in checksums or message integrity checks,
    ignored on reception.


2.  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.

      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                             +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     /                             Data                              /
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Fields:

    Type        139 - NI Query.
                140 - NI Reply.

    Code        For NI Query:

                0   Indicates that the Data field contains an IPv6
                    address which is the Subject of this Query.

                1   Indicates that the Data field contains a domain name
                    which is the Subject of this Query, or is empty, as
                    in the case of a NOOP or Supported Qtypes query.

                2   Indicates that the Data field contains an IPv4
                    address which is the Subject of this Query.

                For NI Reply:




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                0   Indicates a successful reply.  The Reply Data field
                    may or may not be empty.

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

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

    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.  Five values of Qtype are specified in
                this document.

    Flags       Qtype-specific flags which may be defined for certain
                Query types and their Replies.  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 and/or to
                aid in matching Replies with Queries.  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.

    Data        In a Query, the Subject Address or Name.  In a Reply,
                Qtype-specific data present only when the ICMPv6 Code
                field is zero.  The length of the Data may be inferred
                from the IPv6 header's Payload Length field [2460], the
                length of the fixed portion of the NI packet and the
                lengths of the ICMPv6 header and intervening extension
                headers.

    Note that the type of information present in the Data field of a
    Query is inferred from the ICMP Code, while the type of information,
    if any, in the Data field of a Reply is inferred from the Qtype.

    When the Subject of a Query is a name, the name MUST be in DNS wire
    format [1035].  The name may be either a fully-qualified domain
    name, including the terminating zero-length label, or a single DNS
    label followed by two zero-length labels.  Since a Query contains at
    most one DNS name, DNS compression will not be used.




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3.  Message Processing

    The Querier constructs an ICMP NI Query and sends it to the address
    from which information is wanted.  When the Subject of the Query is
    an IPv6 address, that address will normally be used as the IPv6
    destination address of the Query, but need not be if the Querier has
    useful a priori information about the addresses of the target node.
    An NI Query may also be sent to a multicast address of link-local
    scope [2373].

    When the Subject is a domain name, either fully-qualified or
    single-component, and the Querier does not have a unicast address
    for the target node, the query MUST be sent to a link-scope
    multicast address formed in the following way.  The Subject Name is
    converted to canonical form, as defined by DNS Security [2535],
    which is uncompressed with all alphabetic characters in lower case.
    (If additional DNS label types for host names are defined, the rules
    for canonicalizing those labels will be found in the defining
    specification.)  Compute the MD5 hash [1321] of the first label of
    the Subject Name -- the portion beginning with the first one-octet
    length field and up to, but excluding, any subsequent length field.
    Append the first 32 bits of that 128-bit hash to the prefix
    FF02:0:0:0:0:2::/96.  The resulting multicast address will be termed
    the "NI Group Address" for the name.

    The Nonce should be a random or good pseudo-random value to foil
    spoofed replies.  An implementation which allows multiple
    independent processes to send NI queries MAY use the Nonce value to
    deliver Replies to the correct process.  Nonetheless, such processes
    MUST check the received Nonce and ignore extraneous Replies.

    If true communication security is required, IPsec [2401] must be
    used.

    Upon receiving a NI Query, the Responder must check the Query's IPv6
    destination address and discard the Query without further processing
    unless it is one of the Responder's unicast or anycast addresses, or
    a link-local scope multicast address which the Responder has joined.
    Typically the latter will be a NI Group Address for a name belonging
    to the Responder or a NI Group Address for a name for which the
    Responder is providing proxy service.  A node MAY be configurable to
    discard NI Queries to multicast addresses other than its NI Group
    Address(es) but if so, the default configuration MUST be not to
    discard them.

    A Responder must also silently discard a Query whose Subject Address
    or Name (in the Data field) does not belong to that node, unless it
    is providing proxy service for that Subject.  A single-component



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    Subject Name matches any fully-qualified name whose first label
    matches the Subject.  All name matching is done in a case-
    independent manner consistent with DNSSEC name canonicalization
    [2535].

    Next, if Qtype is unknown to the Responder, it must return a NI
    Reply with ICMPv6 Code = 2 and no Reply Data.  The Responder should
    rate-limit such replies as it would ICMPv6 error replies [2463,
    2.4(f)].

    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 a NI Reply with ICMPv6 Code = 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 or a multicast address.
    If the Queried Address was anycast or multicast, the source address
    for the Reply SHOULD be one belonging to the interface on which the
    Query was received.

    If the Query was sent to an anycast or multicast address,
    transmission of the Reply MUST be delayed by a random interval
    between zero and MAX_ANYCAST_DELAY_TIME, as defined by IPv6 Neighbor
    Discovery [2461].


4.  Defined Qtypes

    The following five Qtypes are defined.  The first four (number 0 to
    3) MUST be supported by any implementation of this protocol.  The
    last one SHOULD be supported by any implementation on an IPv4/IPv6
    dual-stack node and MAY be supported on an IPv6-only node.


    0   NOOP.

    1   Supported Qtypes.

    2   DNS Name.

    3   Node Addresses.

    4   IPv4 Addresses.



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4.1.  NOOP

    This NI type has no defined flags and never has a Data field.  A
    Reply to a NI NOOP Query tells the Querier that a node with the
    Queried Address is up and reachable, implements the Node Information
    protocol, and incidentally happens to reveal whether the Queried
    Address was an anycast address.  On transmission, the ICMPv6 Code in
    a NOOP Query must be set to 1 and the Code in a NOOP Reply must be
    0.  On reception of a NOOP Query or Reply, the Code must be ignored.


4.2.  Supported Qtypes

    This Query contains no Data field.  The Reply Data is a bit-vector
    showing which Qtypes are supported by the Responder.  The Reply Data
    has two variant forms: uncompressed and compressed.  The
    uncompressed Data format is one or more complete 32-bit words, each
    word a bitmask with the low-order bit in each word corresponding to
    the lowest numbered Qtype in a group of 32.  The first word
    describes the Responder's support for Qtypes 0 to 31, the second
    word 32 to 63, and so on.

    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 mandatory Qtypes defined in this
    specification.  Thus the Data field of a NI Supported Qtypes Reply
    from a Responder implementing only the mandatory Qtypes will contain
    32 bits in the following form:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0                    . . .                    0 0 0 1 1 1 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    The compressed form of the Reply Data consists of a sequence of
    blocks, each block consisting of two 16-bit unsigned integers, nWord
    and nSkip, followed by nWord 32-bit bitmasks describing the
    Responder's support for 32 consecutive Qtypes.  nSkip is a count of
    32-bit words following the included words which would have been
    all-zero and have been suppressed.  The last block MUST have nSkip =
    0.  As an example, a Responder supporting Qtypes 0, 1, 2, 3, 60, and
    4097 could express that information with the following Reply Data
    (nWord and nSkip fields are written in decimal for easier reading):






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      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               2               |              126              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0                    . . .                    0 0 0 1 1 1 1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 1 0 0 0                    . . .                    0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               1               |               0               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0                      . . .                      0 0 0 1 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    One flag bit is defined.

      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=1            |          unused             |C|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    In a Query, a C-flag set to 1 indicates that the Querier will accept
    the compressed form of the Reply Data.  In a Reply, a C-flag set to
    1 indicates that the Reply Data is compressed.  The compressed form
    MAY be used in a Reply only if the Query had the C-flag set.
    Implementations of this specification SHOULD support the compressed
    form and if they do, SHOULD set the C-flag in all Supported Qtypes
    Queries and SHOULD use the compressed form in Supported Qtypes
    Replies (when allowed by the C-flag in the query) if doing so would
    avoid fragmentation or save significant space in the Reply.


4.3.  DNS Name

    The NI DNS Name Query requests the fully-qualified or single-
    component name corresponding to the Subject Address or Name.  The
    Reply Data has the following format.











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      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                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          DNS Names ...                        |
     +                                                               +
     /                                                               /
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    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.

    DNS Names   The fully-qualified or single-component name or names of
                the Responder which correspond(s) to the Subject Address
                or Name, in DNS wire format [1035].  Each name MUST be
                fully-qualified if the responder knows the domain
                suffix, and otherwise be a single DNS label followed by
                two zero-length labels.

                When multiple DNS names are returned, DNS name
                compression [1035] SHOULD be used, and the offsets are
                counted from the first octet of the Data field.  An
                offset of 4, for example, will point to the beginning of
                the first name.

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

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

        The remaining Valid Lifetime of a prefix from which the Subject
        Address was derived through Stateless Autoconfiguration [2461,
        2462];

        The TTL of an existing AAAA or A6 record which associates the
        Subject Address with the DNS Name being returned.

    If the Responder returns multiple names but considers one name to be
    official or canonical, that name MUST be placed immediately after
    the TTL.




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    Only one TTL is included in the reply.  If the Responder considers
    different names to be cacheable for different times, the TTL field
    must be set no larger than the minimum of those times.

    If the Responder does not know its name at all it MUST send a Reply
    with TTL=0 and no DNS Names.  The Querier will be able to determine
    from the packet length that the Data field contains only a TTL.

    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=2            |          unused             |T|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    A T-flag set to 1 in a NI DNS Name 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.

    If a name rather than an address was the Subject of the Query, the
    T-flag MUST be zero and the TTL SHOULD be zero.

    The information in a NI DNS Name 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 DNS Name 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 DNS Name
    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 DNS Name Query.


4.3.1.  Discussion

    Because a node can only answer a DNS Name 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.




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    IPsec can be applied to NI DNS Name 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 on (or contemplated) between the Querier and Responder.


4.4.  Node Addresses

    The NI Node Addresses Query requests some set of the Responder's
    IPv6 unicast addresses.  The Reply Data is a sequence of 128-bit
    IPv6 addresses, each address preceded by separate a 32-bit TTL
    value, with Preferred addresses listed before Deprecated addresses
    [2461], but otherwise in no special order.  Five flag bits are
    defined in the Query, and six 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=3            |       unused      |G|S|L|C|A|T|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    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.

    C   If set to 1, IPv4-compatible and IPv4-mapped addresses [2373]
        are requested.

    A   If set to 1, all the Responder's unicast addresses (of the
        specified scope(s)) are requested.  If 0, only those addresses
        are requested which belong to the interface (or any one
        interface) which has the Subject Address, or which are
        associated with the Subject Name.

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

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

    The TTL associated with each address are to be determined by the
    rules in section 4.3, applied to the returned address rather than
    the Subject.  If no meaningful caching time can be given for an
    address, the corresponding TTL field MUST be zero.




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    Each address with non-zero TTL in a NI Node Address Reply may be
    cached and used for the period indicated by that TTL.  If the TTL is
    zero, the corresponding address 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.

    IPv4-mapped addresses can only be returned by a Node Information
    proxy, since they represent addresses of IPv4-only nodes, which
    perforce do not implement this protocol.


4.5.  IPv4 Addresses

    The NI IPv4 Addresses Query requests some set of the Responder's
    IPv4 unicast addresses.  The Reply Data is a sequence of 32-bit IPv4
    addresses, each address preceded by a 32-bit TTL value.  One flag
    bit is defined in the Query, and two 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=4            |       unused              |A|T|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    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
        Subject Address.

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

    Flag A is copied from a Query to the corresponding Reply.

    The TTL associated with each address are to be determined by the
    rules in section 4.3, applied to the returned address rather than
    the Subject, excluding the autoconfiguration Valid Lifetime.  If no
    meaningful caching time can be given for an address, the
    corresponding TTL field MUST be zero.

    Each address with non-zero TTL in a NI IPv4 Address Reply may be
    cached and used for the period indicated by that TTL.  If the TTL is
    zero, the corresponding address 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.



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4.5.1.  Discussion

    It is possible that a node may treat IPv4 interfaces and IPv6
    interfaces as distinct, even though they are associated with the
    same hardware.  When such a node is responding to a NI Query having
    a Subject Address of one type requesting the other type, and the
    Query has the A flag set to 0, it SHOULD consider IP interfaces,
    other than tunnels, associated with the same hardware as being the
    same interface.


5.  IANA Considerations

    ICMPv6 type values 139 and 140 have been assigned by IANA for this
    protocol.  This document defines three values of the ICMPv6 Code
    field for each of these ICMPv6 Type values.  Additional Code values
    may be defined only by IETF Consensus [2434].

    This document defines five values of Qtype, numbers 0 through 4.
    Following the policies outlined in "Guidelines for Writing an IANA
    Considerations Section in RFCs" [2434], new values, and their
    associated Flags and Reply Data, may be defined as follows.

         Qtypes 5 through 255, by IETF Consensus.

         Qtypes 256 through 1023, Specification Required.

         Qtypes 1024 through 4095, First Come First Served.

         Qtypes 4096 through 65535, Private Use.

    Users of Private Use values should note that values above 8000 to
    9000 are likely to lead to fragmentation of "Supported Qtypes"
    Replies unless the compressed form of the Reply Data is used.

    Assignment of the multicast address prefix FF02:0:0:0:0:2::/96 used
    in section 3 as a destination for IPv6 Node Information Queries is
    requested.


6.  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 [2535] in the zones used for
    address-to-name translations will be no easier than the maintenance



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    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
    index.


7.  Acknowledgments

    Alain Durand contributed to this specification and valuable feedback
    and implementation experience was provided by Jun-Ichiro Hagino and
    Tatuya Jinmei.  This document is not the first proposal of a direct
    query mechanism for address-to-name translation.  The idea had been
    discussed briefly in the IPng working group and RFC 1788 [1788]
    describes such a mechanism for IPv4.


8.  References


    [1035] P. Mockapetris, "Domain Names - Implementation and
        Specification", RFC 1035, STD 13, November 1987.

    [1321] R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321,
        April 1992.

    [1788] W. Simpson, "ICMP Domain Name Messages", RFC 1788, April
        1995.

    [2119] S. Bradner, "Key words for use in RFCs to Indicate
        Requirement Levels," RFC 2119, March 1997.

    [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, November 1998.

    [2434] Narten, T. and H. T. Alvestrand, "Guidelines for Writing an
        IANA Considerations Section in RFCs", RFC 2434, October 1998.

    [2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
        (IPv6) Specification", RFC 2460, December 1998.

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




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    [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.

    [2535] D. Eastlake 3rd, "Domain Name System Security Extensions",
        RFC 2535, March 1999.

9.  Author's Address

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

    Phone: +1 630 840 3461

    Email: crawdad@fnal.gov






























Expires March 2, 2001           Crawford                       [Page 14]


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