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Versions: (draft-nikander-hip-dns) 00 01 02 03 04 05 06 07 08 09 RFC 5205

Network Working Group                                        P. Nikander
Internet-Draft                             Ericsson Research Nomadic Lab
Expires: April 13, 2006                                      J. Laganier
                                                        DoCoMo Euro-Labs
                                                        October 10, 2005


    Host Identity Protocol (HIP) Domain Name System (DNS) Extensions
                         draft-ietf-hip-dns-03

Status of this Memo

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   This Internet-Draft will expire on April 13, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies two new resource records (RRs) for the Domain
   Name System (DNS), and how to use them with the Host Identity
   Protocol (HIP).  These RRs allow a HIP node to store in the DNS its
   Host Identity (HI, the public component of the node public-private
   key pair), Host Identity Tag (HIT, a truncated hash of its public
   key), and the Domain Name or IP addresses of its rendezvous servers
   (RVS).



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  6
   3.  Usage Scenarios  . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Simple static singly homed end-host  . . . . . . . . . . .  8
     3.2.  Mobile end-host  . . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Mixed Scenario . . . . . . . . . . . . . . . . . . . . . . 10
   4.  Overview of using the DNS with HIP . . . . . . . . . . . . . . 12
     4.1.  Storing HI and HIT in DNS  . . . . . . . . . . . . . . . . 12
       4.1.1.  HI and HIT Verification  . . . . . . . . . . . . . . . 12
     4.2.  Storing Rendezvous Servers in the DNS  . . . . . . . . . . 12
     4.3.  Initiating connections based on DNS names  . . . . . . . . 12
   5.  Storage Format . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.1.  HIPHI RDATA format . . . . . . . . . . . . . . . . . . . . 13
       5.1.1.  PK algorithm format  . . . . . . . . . . . . . . . . . 13
       5.1.2.  HIT length format  . . . . . . . . . . . . . . . . . . 13
       5.1.3.  HIT format . . . . . . . . . . . . . . . . . . . . . . 13
       5.1.4.  Public key format  . . . . . . . . . . . . . . . . . . 13
     5.2.  HIPRVS RDATA format  . . . . . . . . . . . . . . . . . . . 14
       5.2.1.  Preference format  . . . . . . . . . . . . . . . . . . 14
       5.2.2.  Rendezvous server type format  . . . . . . . . . . . . 14
       5.2.3.  Rendezvous server format . . . . . . . . . . . . . . . 15
   6.  Presentation Format  . . . . . . . . . . . . . . . . . . . . . 16
     6.1.  HIPHI Representation . . . . . . . . . . . . . . . . . . . 16
     6.2.  HIPRVS Representation  . . . . . . . . . . . . . . . . . . 16
     6.3.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  Retrieving Multiple HITs and IPs from the DNS  . . . . . . . . 18
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
     8.1.  Attacker tampering with an insecure HIPHI RR . . . . . . . 19
     8.2.  Attacker tampering with an insecure HIPRVS RR  . . . . . . 19
     8.3.  Opportunistic HIP  . . . . . . . . . . . . . . . . . . . . 20
     8.4.  Unpublished Initiator HI . . . . . . . . . . . . . . . . . 20
     8.5.  Hash and HITs Collisions . . . . . . . . . . . . . . . . . 20
     8.6.  DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 22
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     11.1. Normative references . . . . . . . . . . . . . . . . . . . 23
     11.2. Informative references . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
   Intellectual Property and Copyright Statements . . . . . . . . . . 26









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1.  Introduction

   This document specifies two new resource records (RRs) for the Domain
   Name System (DNS) [RFC1034], and how to use them with the Host
   Identity Protocol (HIP) [I-D.ietf-hip-base].  These RRs allow a HIP
   node to store in the DNS its Host Identity (HI, the public component
   of the node public-private key pair), Host Identity Tag (HIT, a
   truncated hash of its HI), and the Domain Name or IP addresses of its
   rendezvous servers (RVS) [I-D.ietf-hip-rvs].

   The current Internet architecture defines two global namespaces: IP
   addresses and domain names.  The Domain Name System provides a two
   way lookup between these two namespaces.  The HIP architecture
   [I-D.ietf-hip-arch] defines a new third namespace, called the Host
   Identity Namespace.  This namespace is composed of Host Identifiers
   (HI) of HIP nodes.  The Host Identity Tag (HIT) is one representation
   of an HI.  This representation is obtained by taking the output of a
   secure hash function applied to the HI, truncated to the IPv6 address
   size.  HITs are supposed to be used in the place of IP addresses
   within most ULPs and applications.

   The Host Identity Protocol [I-D.ietf-hip-base] allows two HIP nodes
   to establish together a HIP Association.  A HIP association is bound
   to the nodes HIs rather than to their IP address(es).

   A HIP node establish a HIP association by initiating a 4 way
   handshake where two parties, the initiator and responder, exchange
   the I1, I2, R1 and R2 HIP packets (see section 5.3 of [I-D.ietf-hip-
   base])


        +-----+                +-----+
        |     |-------I1------>|     |
        |  I  |<------R1-------|  R  |
        |     |-------I2------>|     |
        |     |<------R2-------|     |
        +-----+                +-----+

   Although a HIP node can initiate HIP communication
   "opportunistically", i.e., without prior knowledge of its peer's HI,
   doing so exposes both endpoints to Man-in-the-Middle attacks on the
   HIP handshake and its cryptographic protocol.  Hence, there is a
   desire to gain knowledge of peers' HI before applications and ULPs
   initiate communication.  Because many applications use the Domain
   Name System [RFC1034] to name nodes, DNS is a straightforward way to
   provision nodes with the HIP information (i.e.  HI, HIT and possibly
   RVS) of nodes named in the DNS tree, without introducing or relying
   on an additional piece of infrastructure.  Note that in the absence



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   of DNSSEC [RFC2065], the DNS name resolution is vulnerable to Man-in-
   the-Middle attack (See Section 8), and hence the HIP handshake is
   also vulnerable to a Man-in-the-Middle attack.

   The proposed HIP multi-homing mechanisms [I-D.ietf-hip-mm] allow a
   node to dynamically change its set of underlying IP addresses while
   maintaining IPsec SA and transport layer session survivability.  The
   HIP rendezvous extensions [I-D.ietf-hip-rvs] proposal allows a HIP
   node to maintain HIP reachability while it is changing its current
   location (the node IP address(es)).  This rendezvous service is
   provided by a third party, the node's rendezvous server (RVS).


                    +-----+
           +--I1--->| RVS |---I1--+
           |        +-----+       |
           |                      v
        +-----+                +-----+
        |     |<------R1-------|     |
        |  I  |-------I2------>|  R  |
        |     |<------R2-------|     |
        +-----+                +-----+

   An initiator (I) willing to establish a HIP association with a
   responder (R) would typically initiate a HIP exchange by sending an
   I1 towards the RVS IP address rather than towards the responder IP
   address.  Then, the RVS, noticing that the receiver HIT is not its
   own, but the HIT of a HIP node registered for the rendezvous service,
   would relay the I1 to the responder.  Typically the responder would
   then complete the exchange without further assistance from the RVS by
   sending an R1 directly to the initiator IP address.

   Currently, most of the Internet applications that need to communicate
   with a remote host first translate a domain name (often obtained via
   user input) into one or more IP address(es).  This step occurs prior
   to communication with the remote host, and relies on a DNS lookup.

   With HIP, IP addresses are expected to be used mostly for on-the-wire
   communication between end hosts, while most ULPs and applications use
   HIs or HITs instead (ICMP might be an example of an ULP not using
   them).  Consequently, we need a means to translate a domain name into
   an HI.  Using the DNS for this translation is pretty straightforward:
   We define a new HIPHI (HIP HI) resource record.  Upon query by an
   application or ULP for a FQDN -> IP lookup, the resolver would then
   additionally perform an FQDN -> HI lookup, and use it to construct
   the resulting HI -> IP mapping (which is internal to the HIP layer).
   The HIP layer uses the HI -> IP mapping to translate HIs and their
   local representations (HITs, IPv4 and IPv6-compatible LSIs) into IP



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   addresses and vice versa.

   This draft introduces the following new DNS Resource Records:

      - HIPHI, for storing Host Identifiers and Host Identity Tags

      - HIPRVS, for storing rendezvous server information












































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2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [RFC2119].














































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3.  Usage Scenarios

   In this section, we briefly introduce a number of usage scenarios
   where the DNS is useful with the Host Identity Protocol.

   With HIP, most application and ULPs are unaware of the IP addresses
   used to carry packets on the wire.  Consequently, a HIP node could
   take advantage of having multiple IP addresses for fail-over,
   redundancy, mobility, or renumbering, in a manner which is
   transparent to most ULPs and applications (because they are bound to
   HIs, hence they are agnostic to these IP address changes).

   In these situations, a node wishing to be reachable by reference to
   its FQDN should store the following information in the DNS:

   o  A set of IP address(es) through A and AAAA RRs.

   o  A Host Identity (HI) and/or Host Identity Tag (HIT) through HIPHI
      RRs.

   o  An IP address or DNS name of its rendezvous server(s) (RVS)
      through HIPRVS RRs.

   When a HIP node wants to initiate a communication with another HIP
   node, it first needs to perform a HIP base exchange to set-up a HIP
   association towards its peer.  Although such an exchange can be
   initiated opportunistically, i.e., without prior knowledge of the
   responder's HI, by doing so both nodes knowingly risk man-in-the-
   middle attacks on the HIP exchange.  To prevent these attacks, it is
   recommended that the initiator first obtain the HI of the responder,
   and then initiate the exchange.  This can be done, for example,
   through manual configuration or DNS lookups.  Hence, a new HIPHI RR
   is introduced.

   When a HIP node is frequently changing its IP address(es), the
   dynamic DNS update latency may prevent it from publishing its new IP
   address(es) in the DNS.  For solving this problem, the HIP
   architecture introduces rendezvous servers (RVS).  A HIP host uses a
   rendezvous server as a rendezvous point, to maintain reachability
   with possible HIP initiators.  Such a HIP node would publish in the
   DNS its RVS IP address or DNS name in a HIPRVS RR, while keeping its
   RVS up-to-date with its current set of IP addresses.

   When a HIP node wants to initiate a HIP exchange with a responder it
   will perform a number of DNS lookups.  Depending on the type of the
   implementation, the order in which those lookups will be issued may
   vary.  For instance, implementations using IP address in APIs may
   typically first query for A and/or AAAA records at the responder



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   FQDN, while those using HIT in APIS may typically first query for
   HIPHI records.

   In the following we assume that the initiator first queries for A
   and/or AAAA records at the responder FQDN.

   If the query for the A and/or AAAA was responded to with a DNS answer
   with RCODE=3 (Name Error), then the responder's information is not
   present in the DNS and further queries SHOULD NOT be made.

   In case the query for the address records returned a DNS answer with
   RCODE=0 (No Error), then the initiator sends out two queries: One for
   the HIPHI type and one for the HIPRVS type at the responder's FQDN.

   Depending on the combinations of answer the situations described in
   Section 3.1, Section 3.2 and Section 3.3 can occur.

   Note that storing HIP RR information in the DNS at a FQDN which is
   assigned to a non-HIP node might have ill effects on its reachability
   by HIP nodes.

3.1.  Simple static singly homed end-host

   A HIP node (R) with a single static network attachment, wishing to be
   reachable by reference to its FQDN (www.example.com), would store in
   the DNS, in addition to its IP address(es) (IP-R), its Host Identity
   (HI-R) in a HIPHI resource record.

   An initiator willing to associate with a node would typically issue
   the following queries:

      QNAME=www.example.com, QTYPE=A

      (QCLASS=IN is assumed and omitted from the examples)

   Which returns a DNS packet with RCODE=0 and one or more A RRs A with
   the address of the responder (e.g.  IP-R) in the answer section.

      QNAME=www.example.com, QTYPE=HIPHI

   Which returns a DNS packet with RCODE=0 and one or more HIPHI RRs
   with the HIT and HI (e.g.  HIT-R and HI-R) of the responder in the
   answer section.

      QNAME=www.example.com, QTYPE=HIPRVS

   Which returns a DNS packet with RCODE=0 and an empty answer section.




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   Caption: In the remainder of this document, for the sake of keeping
            diagrams simple and concise, several DNS queries and answers
            are represented as one single transaction, while in fact
            there are several queries and answers flowing back and
            forth, as described in the textual examples.


               [A? HIPRVS? HIPHI?]
               [www.example.com  ]          +-----+
          +-------------------------------->|     |
          |                                 | DNS |
          | +-------------------------------|     |
          | |  [A? HIPRVS? HIPHI?      ]    +-----+
          | |  [www.example.com        ]
          | |  [A IP-R                 ]
          | |  [HIPHI 10 3 2 HIT-R HI-R]
          | v
        +-----+                              +-----+
        |     |--------------I1------------->|     |
        |  I  |<-------------R1--------------|  R  |
        |     |--------------I2------------->|     |
        |     |<-------------R2--------------|     |
        +-----+                              +-----+

3.2.  Mobile end-host

   A mobile HIP node (R) wishing to be reachable by reference to its
   FQDN (www.example.com) would store in the DNS, possibly in addition
   to its IP address(es) (IP-R), its HI (HI-R) in a HIPHI RR, and the IP
   address(es) of its rendezvous server(s) (IP-RVS) in HIPRVS resource
   record(s).  The mobile HIP node also needs to notify its rendezvous
   servers of any change in its set of IP address(es).

   An initiator willing to associate with such mobile node would
   typically issue the following queries:

      QNAME=www.example.com, QTYPE=A

   Which returns a DNS packet with RCODE=0 and an empty answer section.

      QNAME=www.example.com, QTYPE=HIPHI

   Which returns a DNS packet with RCODE=0 and one or more HIPHI RRs
   with the HIT and HI (e.g.  HIT-R and HI-R) of the responder in the
   answer section.

      QNAME=www.example.com, QTYPE=HIPRVS




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   Which returns a DNS packet with RCODE=0 and one or more HIPRVS RRs
   containing IP address(es) (e.g.  IP-RVS) or FQDN(s) of RVS(s).

               [A? HIPRVS? HIPHI?]
               [www.example.com  ]          +-----+
         +--------------------------------->|     |
         |                                  | DNS |
         | +--------------------------------|     |
         | |   [A? HIPRVS? HIPHI?      ]    +-----+
         | |   [www.example.com        ]
         | |   [HIPRVS 1 2 IP-RVS      ]
         | |   [HIPHI 10 3 2 HIT-R HI-R]
         | |
         | |                +-----+
         | | +------I1----->| RVS |-----I1------+
         | | |              +-----+             |
         | | |                                  |
         | | |                                  |
         | v |                                  v
        +-----+                              +-----+
        |     |<---------------R1------------|     |
        |  I  |----------------I2----------->|  R  |
        |     |<---------------R2------------|     |
        +-----+                              +-----+


   The initiator would then send an I1 to one of its RVS.  Following,
   the RVS will relay the I1 up to the mobile node, which will complete
   the HIP exchange.

3.3.  Mixed Scenario

   A HIP node might be configured with more than one IP address (multi-
   homed), or rendezvous server (multi-reachable).  In these cases, it
   is possible that the DNS returns multiple A or AAAA RRs, as well as
   HIPRVS containing one or multiple rendezvous servers.  In addition to
   its set of IP address(es) (IP-R1, IP-R2), a multi-homed end-host
   would store in the DNS its HI (HI-R) in a HIPHI RR, and possibly the
   IP address(es) of its RVS(s) (IP-RVS1, IP-RVS2) in HIPRVS RRs.

   An initiator willing to associate with such a node would typically
   issue the following queries:

      QNAME=www.example.com, QTYPE=A

   Which returns a DNS packet with RCODE=0 and one or more A or AAAA RRs
   containing IP address(es) (e.g.  IP-R1 and IP-R2) in the answer
   section.



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      QNAME=www.example.com, QTYPE=HIPHI

   Which returns a DNS packet with RCODE=0 and one or more HIPHI RRs
   with the HIT and HI (e.g.  HIT-R and HI-R) of the responder in the
   answer section.

      QNAME=www.example.com, QTYPE=HIPRVS

   Which returns a DNS packet with RCODE=0 and one or more HIPRVS RRs
   containing IP address(es) (e.g.  IP-RVS1, IP-RVS2) or FQDN(s) of
   RVS(s).

               [A? HIPRVS? HIPHI?]
               [www.example.com  ]          +-----+
         +--------------------------------->|     |
         |                                  | DNS |
         | +--------------------------------|     |
         | |   [A? HIPRVS? HIPHI?      ]    +-----+
         | |   [www.example.com        ]
         | |   [A IP-R1                ]
         | |   [A IP-R2                ]
         | |   [HIPRVS 1 2 IP-RVS1     ]
         | |   [HIPRVS 1 2 IP-RVS2     ]
         | |   [HIPHI 10 3 2 HIT-R HI-R]
         | |
         | |               +------+
         | | +-----I1----->| RVS1 |------I1------+
         | | |             +------+              |
         | v |                                   v
        +-----+                               +-----+
        |     |---------------I1------------->|     |
        |     |                               |     |
        |  I  |<--------------R1--------------|  R  |
        |     |---------------I2------------->|     |
        |     |<--------------R2--------------|     |
        +-----+                               +-----+
             |                                   ^
             |             +------+              |
             +-----I1----->| RVS2 |------I1------+
                           +------+











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4.  Overview of using the DNS with HIP

4.1.  Storing HI and HIT in DNS

   Any conforming implementation may store a Host Identity (HI) and its
   associated Host Identity Tag (HIT) in a DNS HIPHI RDATA format.  If a
   particular form of an HI does not already have a specified RDATA
   format, a new RDATA-like format SHOULD be defined for the HI.  HI and
   HIT are defined in Section 3 of [I-D.ietf-hip-base].

4.1.1.  HI and HIT Verification

   Upon return of a HIPHI RR, a host MUST always calculate the HI-
   derivative HIT to be used in the HIP exchange, as specified in
   Section 3 of the HIP base specification [I-D.ietf-hip-base], while
   the HIT possibly embedded along SHOULD only be used as an
   optimization (e.g. table lookup).

4.2.  Storing Rendezvous Servers in the DNS

   The HIP rendezvous server (HIPRVS) resource record indicates an
   address or a domain name of a rendezvous Server, towards which a HIP
   I1 packet might be sent to trigger the establishment of an
   association with the entity named by this resource record [I-D.ietf-
   hip-rvs].

   An RVS receiving such an I1 would then relay it to the appropriate
   responder (the owner of the I1 receiver HIT).  The responder will
   then complete the exchange with the initiator, typically without
   ongoing help from the RVS.

   Any conforming implementation may store rendezvous server's IP
   address(es) or DNS name in a DNS HIPRVS RDATA format.  If a
   particular form of a RVS reference does not already have a specified
   RDATA format, a new RDATA-like format SHOULD be defined for the RVS.

4.3.  Initiating connections based on DNS names

   On a HIP node, a Host Identity Protocol exchange SHOULD be initiated
   whenever an Upper Layer Protocol attempt to communicate with an
   entity and the DNS lookup returns HIPHI and/or HIPRVS resource
   records.  If a DNS lookup returns one or more HIPRVS RRs and no A nor
   AAAA RRs, the afore mentioned HIP exchange SHOULD be initiated
   towards one of these RVS [I-D.ietf-hip-base].  Since some hosts may
   choose not to have HIPHI information in DNS, hosts MAY implement
   support for opportunistic HIP.





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5.  Storage Format

5.1.  HIPHI RDATA format

   The RDATA for a HIPHI RR consists of a public key algorithm type, the
   HIT length, a HIT, and a public key.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | PK algorithm  |   HIT length  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+             HIT               |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               /
   /                          Public Key                           /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|


   The PK algorithm, HIT length, HIT and Public Key field are REQUIRED.

5.1.1.  PK algorithm format

   The PK algorithm field indicates the public key cryptographic
   algorithm and the implied public key field format.  This document
   reuse the values defined for the 'algorithm type' of the IPSECKEY RR
   [RFC4025] 'gateway type' field.

   The presently defined values are given only informally:

      1 A DSA key is present, in the format defined in RFC2536
      [RFC2536].

      2 A RSA key is present, in the format defined in RFC3110
      [RFC3110].

5.1.2.  HIT length format

   The HIT length indicates the length in bytes of the HIT field.

5.1.3.  HIT format

   The HIT is stored, as a binary value, in network byte order.

5.1.4.  Public key format

   Both of the public key types defined in this document (RSA and DSA)



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   reuse the public key formats defined for the IPSECKEY RR [RFC4025]
   (which in turns contains the algorithm-specific portion of the KEY RR
   RDATA, all of the KEY RR DATA after the first four octets,
   corresponding to the same portion of the KEY RR that must be
   specified by documents that define a DNSSEC algorithm).

   In the future, if a new algorithm is to be used both by IPSECKEY RR
   and HIPHI RR, it would probably use the same public key encoding for
   both RRs.  Unless specified otherwise, the HIPHI public key field
   would use the same public key format as the IPSECKEY RR RDATA for the
   corresponding algorithm.

   The DSA key format is defined in RFC2536 [RFC2536].

   The RSA key format is defined in RFC3110 [RFC3110] and the RSA key
   size limit (4096 bits) is relaxed in the IPSECKEY RR [RFC4025]
   specification.

5.2.  HIPRVS RDATA format

   The RDATA for a HIPRVS RR consists of a preference value, a
   rendezvous server type and either one or more rendezvous server
   address, or one rendezvous server domain name.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  preference   |     type      |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      rendezvous server        |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Preference and RVS Type fields are REQUIRED.  At least one RVS
   field MUST be present.

5.2.1.  Preference format

   This is an unsigned 8-bit value, used to specify the preference given
   to the RVS in the HIPRVS RR amongst others at the same owner.  RVSs
   with lower values are preferred.  If there is a tie within some RR
   subset, the initiating HIP host should pick one of the RVS randomly
   from the set of RRs, such that the requester load is fairly balanced
   amongst all RVSs of the set.

5.2.2.  Rendezvous server type format

   The rendezvous server type indicates the format of the information
   stored in the rendezvous server field.



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   This document reuses the type values for the 'gateway type' field of
   the IPSECKEY RR [RFC4025].  The presently defined values are given
   only informally:

   1.  One or more 4-byte IPv4 address(es) in network byte order are
       present.

   2.  One or more 16-byte IPv6 address(es) in network byte order are
       present.

   3.  One or more variable length wire-encoded domain names as
       described in section 3.3 of RFC1035 [RFC1035].  The wire-encoded
       format is self-describing, so the length is implicit.  The domain
       names MUST NOT be compressed.

5.2.3.  Rendezvous server format

   The rendezvous server field indicates one or more rendezvous
   server(s) IP address(es), or domain name(s).  A HIP I1 packet sent to
   any of these RVS would reach the entity named by this resource
   record.

   This document reuses the format used for the 'gateway' field of the
   IPSECKEY RR [RFC4025], but allows to concatenate several IP (v4 or
   v6) addresses.  The presently defined formats for the data portion of
   the rendezvous server field are given only informally:

   o  One or more 32-bit IPv4 address(es) in network byte order.

   o  One or more 128-bit IPv6 address(es) in network byte order.

   o  One or more variable length wire-encoded domain names as described
      in Section 3.3 of RFC1035 [RFC1035].  The wire-encoded format is
      self-describing, so the length is implicit.  The domain names MUST
      NOT be compressed.
















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6.  Presentation Format

   This section specifies the representation of the HIPHI and HIPRVS RR
   in a zone data master file.

6.1.  HIPHI Representation

   The PK algorithm field is represented as unsigned integers.

   The HIT length field is not represented as it is implicitly known
   thanks to the HIT field representation.

   The HIT field is represented as the Base16 encoding [RFC3548] (a.k.a.
   hex or hexadecimal) of the HIT.  The encoding MUST NOT contains
   whitespace(s).

   The Public Key field is represented as the Base64 encoding [RFC3548]
   of the public key.  The encoding MAY contains whitespace(s), and such
   whitespace(s) MUST be ignored.

   The complete representation of the HPIHI record is:

   IN  HIPHI ( pk-algorithm
               base16-encoded-hit
               base64-encoded-public-key )

6.2.  HIPRVS Representation

   The RVS field is represented by one or more:

   o  IPv4 dotted decimal address(es)

   o  IPv6 colon hex address(es)

   o  uncompressed domain name(s)

   The complete representation of the HPIRVS record is:


   IN  HIPRVS  ( preference rendezvous-server-type
                 rendezvous-server[1]
                         ...
                 rendezvous-server[n] )

6.3.  Examples

   Example of a node with a HI and a HIT:




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   www.example.com  IN  HIPHI ( 2 2A20E0FF0FE8A52422D059FFFEA938A1
                                AB3NzaC1kc3MAAACBAOBhKn
                                TCPOuFBzZQX/N3O9dm9P9iv
                                UIMoId== )

   Example of a node with an IPv6 RVS:

   www.example.com  IN  HIPRVS (10 2 2001:db8:200:1:20c:f1ff:feb:a533 )

   Example of a node with three IPv4 RVS:

   www.example.com  IN  HIPRVS ( 10 1 192.0.1.2 192.0.2.2 192.0.3.2 )

   Example of a node with two named RVS:

   www.example.com  IN  HIPRVS ( 10 3 rvs.uk.example.com
                                      rvs.us.example.com )


































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7.  Retrieving Multiple HITs and IPs from the DNS

   If a host receives multiple HITs in a response to a DNS query, those
   HITs MUST be considered to denote a single service, and be
   semantically equivalent from that point of view.  When initiating a
   base exchange with the denoted service, the host SHOULD be prepared
   to accept any of HITs as the peer's identity.  A host MAY implement
   this by using the opportunistic mode (destination HIT null in I1), or
   by sending multiple I1s, if needed.

   In particular, if a host receives multiple HITs and multiple IP
   addresses in response to a DNS query, the host cannot know how the
   HITs are reachable at the listed IP addresses.  The mapping may be
   any, i.e., all HITs may be reachable at all of the listed IP
   addresses, some of the HITs may be reachable at some of the IP
   addresses, or there may even be one-to-one mapping between the HITs
   and IP addresses.  In general, the host cannot know the mapping and
   MUST NOT expect any particular mapping.

   It is RECOMMENDED that if a host receives multiple HITs, the host
   SHOULD first try to initiate the base exchange by using the
   opportunistic mode.  If the returned HIT does not match with any of
   the expected HITs, the host SHOULD retry by sending further I1s, one
   at time, trying out all of the listed HITs.  If the host receives an
   R1 for any of the I1s, the host SHOULD continue to use the successful
   IP address until an R1 with a listed HIT is received, or the host has
   tried all HITs, and try the other IP addresses only after that.  A
   host MAY also send multiple I1s in parallel, but sending such I1s
   MUST be rate limited to avoid flooding (as per Section 8.4.1 of
   [I-D.ietf-hip-base]).





















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8.  Security Considerations

   Though the security considerations of the HIP DNS extensions still
   need to be more investigated and documented, this section contains a
   description of the known threats involved with the usage of the HIP
   DNS extensions.

   In a manner similar to the IPSECKEY RR [RFC4025], the HIP DNS
   Extensions allows to provision two HIP nodes with the public keying
   material (HI) of their peer.  These HIs will be subsequently used in
   a key exchange between the peers.  Hence, the HIP DNS Extensions
   introduce the same kind of threats that IPSECKEY does, plus threats
   caused by the possibility given to a HIP node to initiate or accept a
   HIP exchange using "opportunistic" or "unpublished initiator HI"
   modes.

   A HIP node SHOULD obtain both the HIPHI and HIPRVS RRs from a trusted
   party trough a secure channel insuring proper data integrity of the
   RRs.  DNSSEC [RFC2065] provides such a secure channel.

   In the absence of a proper secure channel, both parties are
   vulnerable to MitM and DoS attacks, and unrelated parties might be
   subject to DoS attacks as well.  These threats are described in the
   following sections.

8.1.  Attacker tampering with an insecure HIPHI RR

   The HIPHI RR contains public keying material in the form of the named
   peer's public key (the HI) and its secure hash (the HIT).  Both of
   these are not sensitive to attacks where an adversary gains knowledge
   of them.  However, an attacker that is able to mount an active attack
   on the DNS, i.e., tampers with this HIPHI RR (e.g. using DNS
   spoofing) is able to mount Man-in-the-Middle attacks on the
   cryptographic core of the eventual HIP exchange (responder's HIPHI
   and HIPRVS rewritten by the attacker).

8.2.  Attacker tampering with an insecure HIPRVS RR

   The HIPRVS RR contains a destination IP address where the named peer
   is reachable by an I1 (HIP Rendezvous Extensions IPSECKEY RR
   [I-D.ietf-hip-rvs] ).  Thus, an attacker able to tamper with this RR
   is able to redirect I1 packets sent to the named peer to a chosen IP
   address, for DoS or MitM attacks.  Note that this kind of attacks is
   not specific to HIP and exists independently to whether or not HIP
   and the HIPRVS RR are used.  Such an attacker might tamper with A and
   AAAA RRs as well.

   An attacker might obviously use these two attacks in conjunction: It



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   will replace the responder's HI and RVS IP address by its owns in a
   spoofed DNS packet sent to the initiator HI, then redirect all
   exchanged packets to him and mount a MitM on HIP.  In this case HIP
   won't provide confidentiality nor initiator HI protection from
   eavesdroppers.

8.3.  Opportunistic HIP

   A HIP initiator may not be aware of its peer's HI, and/or its HIT
   (e.g. because the DNS does not contains HIP material, or the resolver
   isn't HIP-enabled), and attempt an opportunistic HIP exchange towards
   its known IP address, filling the responder HIT field with zeros in
   the I1 header.  Such an initiator is vulnerable to a MitM attack
   because it can't validate the HI and HIT contained in a replied R1.
   Hence, an implementation MAY choose not to use opportunistic mode.

8.4.  Unpublished Initiator HI

   A HIP initiator may choose to use an unpublished HI, which is not
   stored in the DNS by means of a HIPHI RR.  A responder associating
   with such an initiator knowingly risks a MitM attack because it
   cannot validate the initiator's HI.  Hence, an implementation MAY
   choose not to use unpublished mode.

8.5.  Hash and HITs Collisions

   As many cryptographic algorithm, some secure hashes (e.g.  SHA1, used
   by HIP to generate a HIT from an HI) eventually become insecure,
   because an exploit has been found in which an attacker with a
   reasonable computation power breaks one of the security features of
   the hash (e.g. its supposed collision resistance).  This is why a HIP
   end-node implementation SHOULD NOT authenticate its HIP peers based
   solely on a HIT retrieved from DNS, but SHOULD rather use HI-based
   authentication.

8.6.  DNSSEC

   In the absence of DNSSEC, the HIPHI and HIPRVS RRs are subject to the
   threats described in RFC 3833 [RFC3833].












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9.  IANA Considerations

   IANA needs to allocate two new RR type code for HIPHI and HIPRVS from
   the standard RR type space.

   IANA does not need to open a new registry for the HIPHI RR type for
   public key algorithms because the HIPHI RR reuse 'algorithms types'
   defined for the IPSECKEY RR [RFC4025].  The presently defined numbers
   are given here only informally:

      0 is reserved

      1 is RSA

      2 is DSA

   IANA does not need to open a new registry for the HIPRVS RR
   rendezvous server type because the HIPHI RR reuse the 'gateway types'
   defined for the IPSECKEY RR [RFC4025].  The presently defined numbers
   are given here only informally:

      0 is reserved

      1 is IPv4

      2 is IPv6

      3 is a wire-encoded uncompressed domain name























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10.  Acknowledgments

   As usual in the IETF, this document is the result of a collaboration
   between many people.  The authors would like to thanks the author
   (Michael Richardson), contributors and reviewers of the IPSECKEY RR
   [RFC4025] specification, which this document was framed after.  The
   authors would also like to thanks the following people, who have
   provided thoughtful and helpful discussions and/or suggestions, that
   have helped improving this document: Rob Austein, Hannu Flinck, Tom
   Henderson, Olaf Kolkman, Miika Komu, Andrew McGregor, Erik Nordmark,
   and Gabriel Montenegro.  Some parts of this draft stem from
   [I-D.ietf-hip-base].

   Julien Laganier is partly funded by Ambient Networks, a research
   project supported by the European Commission under its Sixth
   Framework Program.  The views and conclusions contained herein are
   those of the authors and should not be interpreted as necessarily
   representing the official policies or endorsements, either expressed
   or implied, of the Ambient Networks project or the European
   Commission.































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11.  References

11.1.  Normative references

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2065]  Eastlake, D. and C. Kaufman, "Domain Name System Security
              Extensions", RFC 2065, January 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2536]  Eastlake, D., "DSA KEYs and SIGs in the Domain Name System
              (DNS)", RFC 2536, March 1999.

   [RFC3110]  Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain
              Name System (DNS)", RFC 3110, May 2001.

   [RFC3363]  Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
              Hain, "Representing Internet Protocol version 6 (IPv6)
              Addresses in the Domain Name System (DNS)", RFC 3363,
              August 2002.

   [RFC3548]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 3548, July 2003.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              October 2003.

   [RFC4025]  Richardson, M., "A Method for Storing IPsec Keying
              Material in DNS", RFC 4025, March 2005.

   [I-D.ietf-hip-base]
              Moskowitz, R., "Host Identity Protocol",
              draft-ietf-hip-base-03 (work in progress), June 2005.

   [I-D.ietf-hip-rvs]
              Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
              Rendezvous Extension", draft-ietf-hip-rvs-04 (work in
              progress), October 2005.






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11.2.  Informative references

   [I-D.ietf-hip-arch]
              Moskowitz, R. and P. Nikander, "Host Identity Protocol
              Architecture", draft-ietf-hip-arch-03 (work in progress),
              August 2005.

   [I-D.ietf-hip-mm]
              Nikander, P., "End-Host Mobility and Multihoming with the
              Host Identity Protocol", draft-ietf-hip-mm-02 (work in
              progress), July 2005.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC3833]  Atkins, D. and R. Austein, "Threat Analysis of the Domain
              Name System (DNS)", RFC 3833, August 2004.

































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Authors' Addresses

   Pekka Nikander
   Ericsson Research Nomadic Lab
   JORVAS  FIN-02420
   FINLAND

   Phone: +358 9 299 1
   Email: pekka.nikander@nomadiclab.com


   Julien Laganier
   DoCoMo Communications Laboratories Europe GmbH
   Landsberger Strasse 312
   Munich  80687
   Germany

   Phone: +49 89 56824 231
   Email: julien.ietf@laposte.net
   URI:   http://www.docomolab-euro.com/































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Acknowledgment

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