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Versions: (draft-eggert-hip-rvs) 00 01 02 03 04 05 RFC 5204

HIP Working Group                                            J. Laganier
Internet-Draft                                    LIP / Sun Microsystems
Expires: April 18, 2005                                        L. Eggert
                                                                     NEC
                                                        October 18, 2004


           Host Identity Protocol (HIP) Rendezvous Extensions
                         draft-ietf-hip-rvs-00

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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   This Internet-Draft will expire on April 18, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document discusses rendezvous extensions for the Host Identity
   Protocol (HIP).  Rendezvous mechanisms extend HIP for communication
   with HIP Rendezvous Servers.  Rendezvous Servers improve operation
   when HIP nodes are multi-homed or mobile.  The first part of his
   document motivates the need for rendezvous mechanisms; the second
   part describes the protocol extensions in detail.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Communication Between HIP Nodes  . . . . . . . . . . . . . . .  4
   4.  Communication Between Mobile or Multi-Homed HIP Nodes  . . . .  6
     4.1   Mobility and Multi-Homing with DNS Updates . . . . . . . .  6
     4.2   Mobility and Multi-Homing with Rendezvous Servers  . . . .  8
   5.  HIP Extensions for Rendezvous Servers  . . . . . . . . . . . . 10
     5.1   Additional RVS_CAPABLE Control Field . . . . . . . . . . . 10
     5.2   Additional HIP Parameters  . . . . . . . . . . . . . . . . 10
       5.2.1   RVA_REQUEST Parameter Format and Processing  . . . . . 10
       5.2.2   RVA_REPLY Parameter Format and Processing  . . . . . . 12
       5.2.3   RVA_HMAC Parameter Format and Processing . . . . . . . 12
       5.2.4   FROM Parameter Format and Processing . . . . . . . . . 13
       5.2.5   TO Parameter Format and Processing . . . . . . . . . . 14
       5.2.6   VIA_RVS Parameter Format and Processing  . . . . . . . 15
     5.3   Use of Existing HIP Messages and Parameters  . . . . . . . 16
       5.3.1   ECHO_REQUEST and ECHO_REPLY Parameters . . . . . . . . 16
       5.3.2   REA Parameter  . . . . . . . . . . . . . . . . . . . . 16
   6.  Diagram Notation . . . . . . . . . . . . . . . . . . . . . . . 17
   7.  Establishing Rendezvous Associations . . . . . . . . . . . . . 17
   8.  Establishing HIP Associations via Rendezvous Servers . . . . . 20
     8.1   Sending a Redirect in Reply to I1  . . . . . . . . . . . . 20
     8.2   Passing I1 onto an ESP SA  . . . . . . . . . . . . . . . . 21
     8.3   Rewriting I1 Destination IP Address  . . . . . . . . . . . 22
     8.4   Rewriting I1 Source and Destination IP Addresses . . . . . 23
     8.5   Rewriting I1 and R1 Source and Destination IP Addresses  . 24
     8.6   Cascading Rendezvous Servers . . . . . . . . . . . . . . . 26
     8.7   Implication on the HIP integrity checks  . . . . . . . . . 27
       8.7.1   Checksum . . . . . . . . . . . . . . . . . . . . . . . 27
       8.7.2   HMAC and SIGNATURE . . . . . . . . . . . . . . . . . . 27
       8.7.3   Example  . . . . . . . . . . . . . . . . . . . . . . . 28
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28
   10.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 29
   11.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 29
   12.   References . . . . . . . . . . . . . . . . . . . . . . . . . 30
   12.1  Normative References . . . . . . . . . . . . . . . . . . . . 30
   12.2  Informative References . . . . . . . . . . . . . . . . . . . 31
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 31
   A.  Document Revision History  . . . . . . . . . . . . . . . . . . 32
       Intellectual Property and Copyright Statements . . . . . . . . 33









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1.  Introduction

   The current Internet uses two global namespaces: domain names and IP
   addresses.  The Domain Name System (DNS) provides a two-way lookup
   service between the two [1].  Domain names are symbolic identifiers
   for sets of IP addresses.

   IP addresses have two uses.  First, they are topological locators for
   network attachment points.  Second, they act as names for the
   attached network interfaces.  Saltzer [11] discusses these naming
   concepts in detail.

   Routing and other network-layer mechanisms are based on the locator
   aspects of IP addresses.  Transport-layer protocols and mechanisms
   typically use IP addresses in their role as names for communication
   endpoints.

   This dual use of IP addresses limits the flexibility of the Internet
   architecture.  The need to avoid readdressing in order to maintain
   existing transport-layer connections complicates advanced
   functionality, such as mobility, multi-homing, or network
   composition.

   The Host Identity Protocol (HIP) architecture [2] defines a new third
   namespace.  The Host Identity namespace decouples the name and
   locator roles currently filled by IP addresses.  Instead of mapping
   domain names directly into IP addresses, HIP maps domain names into
   Host Identities, and Host Identities into IP addresses.
   Transport-layer mechanisms operate on Host Identities instead of
   using IP addresses as endpoint names.  Network-layer mechanisms
   continue to use IP addresses as pure locators.

   Without HIP, nodes establish transport-layer connections by first
   looking up the fully-qualified domain name (FQDN) of a peer in the
   DNS.  A successful DNS lookup returns the peer's IP addresses.  A
   node uses one of the returned IP addresses to initiate
   transport-layer communication with a peer node.

   HIP nodes will also look up the domain name of desired peers in the
   DNS, as specified in the HIP DNS Extensions[3].  When a successful
   lookup includes a peer's Host Identities, HIP nodes perform a HIP
   Base Exchange before establishing transport-layer connections.  The
   HIP Base Exchange authenticates the end hosts and can bootstrap
   encryption of the subsequent communication with IPsec [12].  The HIP
   specification [4] discusses the details of the Base Exchange and the
   related protocol exchanges.

   After the Base Exchange, HIP nodes use Host Identities instead of IP



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   addresses for transport-layer connections with a peer.  The HIP layer
   in the network stack internally translates Host Identities (HI) into
   network-layer IP addresses.  This additional mapping between Host
   Identities and IP addresses (HI->IP) is logically separate from the
   first mapping between fully-qualified domain names and Host
   Identities (FQDN->HI).

   For application and transport-layer compatibility, the FQDN->HI
   mapping must remain in the DNS.  However, the HI->IP mapping is
   internal to the HIP layer and may be performed in a number of ways.
   Different lookup mechanism may support communication between two
   mobile or multi-homed HIP nodes better [5].

2.  Terminology

   Rendezvous Server (RVS): A HIP enabled node which relays incoming HIP
   I1 packets to the owner of the receiver HIT contained in the I1
   header.  A RVS may also relay back an R1 to an opportunistic
   Initiator.

   Rendezvous Association (RVA): A lightweight HIP association
   established between a HIP node and its RVS.  The associated state
   doesn't require communication to be maintained and contains the
   peer's HIT, two symmetric integrity keys, and the IP addresses of
   both nodes.

   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 RFC 2119 [6].

3.  Communication Between HIP Nodes

   In the current Internet, the DNS provides a FQDN->IP mapping.  With
   HIP, it must continue to provide a mapping based on domain names.
   This allows transport-layer connections to bind to Host Identities
   instead of IP addresses transparently.

   Instead of mapping domain names directly into IP addresses
   (FQDN->IP), with HIP the DNS maps them to Host Identities (FQDN->HI).
   In a second step, another lookup that is internal to the HIP-layer
   translates the Host Identities into IP addresses for network-layer
   delivery (HI->IP).

   Several alternative approaches are possible for maintaining the
   HI->IP information.  The DNS can maintain this mapping along with the
   FQDN->HI mapping.  Alternatively, a database separate from the DNS
   can manage this information.  This section discusses the different
   approaches and their implications on communication between two HIP



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   nodes.

   The HIP architecture, protocol and DNS extensions specifications
   suggest storing Host Identities along with a node's IP addresses in
   the DNS [3][2][4].  The index for both tables will be domain names.
   Logically, the DNS will thus contain two separate mappings: FQDN->HI
   and FQDN->IP.

   Figure 1 shows the lookup steps and HIP Base Exchange when a node's
   Host Identities are stored alongside its IP addresses.  In step #1,
   the Initiator I performs a DNS lookup on R's domain name FQDN(R).
   The DNS server responds with both R's Host Identities HI(R) and its
   IP addresses IP(R) in step #2 (Details can be found in  [4]).

   The Initiator I uses both pieces of information to perform the HIP
   Base Exchange with R in step #3.  (The details of the Base Exchange,
   specified in [4], are not relevant to this discussion and will thus
   be omitted.)

                       #1 FQDN(R)      +----------+
                 +-------------------->|   DNS    |
                 | +-------------------|          |
                 | |  #2 HI(R), IP(R)  | FQDN->HI |
                 | |                   | FQDN->IP |
                 | |                   +----------+
                 | V
               +-----+       #3 HIP Base Exchange      +-----+
               |     |-------------------------------->|     |
               |  I  |<--------------------------------|  R  |
               |     |-------------------------------->|     |
               |     |<--------------------------------|     |
               +-----+                                 +-----+

                 Figure 1: HIP Lookup and Base Exchange

   Note that the DNS does not currently store the HI->IP mapping
   directly.  Instead, a DNS lookup on a domain name returns both its
   FQDN->HI and FQDN->IP entries.  The HIP stack then implicitly
   constructs the HI->IP mapping based on the HI and IP information
   returned by the DNS lookup.  In the example in Figure 1, the FQDN(R)
   lookup in step #1 returns both HI(R) and IP(R) in step #2.  HIP
   implicitly constructs the HI(R)->IP(R) mapping based on the
   assumption that HI(R) is reachable at IP(R).

   One disadvantage of this approach is that a node's domain name is
   required to obtain both its Host Identities and its IP addresses.
   Even if a HIP node already knows the Host Identity of a HIP peer
   through other means, it cannot currently obtain the peer's IP



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   addresses through the DNS.  The DNS does not maintain an explicit
   HI->IP table, but instead indexes Host Identities only by domain
   names.

   A reverse HI->FQDN DNS mapping could address this limitation.  HIP
   nodes would then look up a HIP peer's domain name through its Host
   Identity.  They would then use the returned domain name to find the
   peer's IP addresses in a second lookup.  However, the DNS may not be
   structurally suited to maintain the reverse HIP->FQDN mapping.  As
   the main Internet-wide database, the DNS is already being overloaded
   with functionality that might be better handled with new mechanisms
   [13].  Finally, the additional reverse lookup would increase the
   latency of the HIP Base Exchange.

4.  Communication Between Mobile or Multi-Homed HIP Nodes

   HIP decouples domain names from IP addresses.  Because transport
   protocols bind to Host Identities, they remain unaware if the set of
   IP addresses associated with a Host Identity changes.  This change
   can have various reasons, including, but not limited to, mobility and
   multi-homing.

   Proposed extensions for mobility and multi-homing [5] allow a HIP
   node to notify its peers about changes in its set of IP addresses.
   These extensions require an established HIP association between two
   nodes, i.e., a completed HIP Base Exchange.

   In addition to notifying its current peers about changes in its IP
   addresses, a HIP node must also update its HI->IP mapping in response
   to IP address changes.  Otherwise, HIP Base Exchanges from new peers
   could fail because they try to contact the node at an IP address it
   is no longer reachable at.

4.1  Mobility and Multi-Homing with DNS Updates

   If the DNS indirectly maintains the HI->IP mapping in a FQDN->IP
   table, nodes can dynamically update their DNS entry in a secure
   fashion [7][8].  The DNS server maintaining the information will then
   sign and distribute the updated zone.












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              #2 FQDN(R)     +----------+
       +-------------------->|   DNS    |
       | +-------------------|          |<------+
       | |  #3 HI(R), IP(R)  | FQDN->HI |       | #1 Update
       | |                   | FQDN->IP |       |    FQDN(R)->IP(R)
       | |                   +----------+       |    whenever IP(R)
       | V                                      |    changes.
     +-----+       #4 HIP Base Exchange      +-----+
     |     |-------------------------------->|     |
     |  I  |<--------------------------------|  R  |
     |     |-------------------------------->|     |
     |     |<--------------------------------|     |
     +-----+                                 +-----+

        Figure 2: HIP Lookup and Base Exchange with DNS Updates

   Figure 2 shows an example of this scenario.  In step #1, R registers
   its FQDN(R)->IP(R) entry in the DNS.  It will dynamically update the
   DNS entry whenever its IP addresses IP(R) change.  Because the DNS
   always contains R's current IP addresses, node I can perform a HIP
   Base Exchange with R at its new IP address (steps #2-4).

   One drawback of using dynamic DNS updates in this way is the cost of
   updating secure zones.  Re-signing an entire zone whenever the IP
   addresses of one entry change places a high cost on the DNS server.
   Using dynamic DNS to update HI->IP mappings may thus not be
   appropriate when changes of IP addresses are frequent.

   A simple, operational change could help limit the costs of frequent
   DNS updates.  Instead of recomputing a zone after each dynamic
   update, a DNS server could aggregate the modifications and only
   perform zone updates periodically.  The disadvantage of this approach
   is that HIP nodes may be unreachable until the DNS server distributes
   the updated zone.

   Another concern with using the DNS to support HIP node mobility is
   the propagation time of updated DNS entries.  DNS servers frequently
   cache DNS responses to reduce the load on the primary servers.
   During the time-to-live associated with a DNS response, DNS servers
   may answer additional requests for the same DNS entry from their
   local caches instead of contacting the primary servers.  Thus, even
   after a HIP node updates its DNS entry, the DNS can still serve the
   old entry until the cached responses expire.  This can lead to
   communication problems, because peers may try to contact a HIP node
   at an IP address it is no longer reachable at.






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4.2  Mobility and Multi-Homing with Rendezvous Servers

   The HIP architecture tries to greatly reduce the frequency of Dynamic
   DNS updates by introducing Rendezvous Servers [2].  Instead of
   registering its current set of IP addresses in its HI->IP entry in
   the DNS, a HIP node may instead register the IP addresses of its
   Rendezvous Servers.  Because the IP addresses of Rendezvous Servers
   are assumed to change only infrequently, this approach can
   significantly reduce the load on DNS servers.

   Rendezvous Servers maintain a mapping between the Host Identities of
   HIP nodes for which they provide service and the node's current IP
   addresses.  HIP nodes must notify their Rendezvous Servers about any
   changes in their IP addresses.  This approach effectively relocates
   the HI->IP information - and the burden of keeping it current - from
   the DNS to the Rendezvous Servers.  This can reduce update costs
   under the assumption that Rendezvous Servers provide more efficient
   ways of maintaining HI->IP tables.

   When a packet destined for one of its HIP nodes arrives at a
   Rendezvous Server, it relays the packet to one of the HIP node's
   current IP addresses.  Due to the specifics of the HIP, only the
   first packet of a HIP Base Exchange will require such relaying [2].
   Subsequent packet of the HIP Base Exchange and all further data
   packets will directly flow between the HIP nodes, bypassing the
   Rendezvous Server.

























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               #3 FQDN(R)      +----------+ #2 Register IP(RVS) in
        +--------------------->|   DNS    |    FQDN(R)->IP(RVS).
        | +--------------------|          |<------------------+
        | |  #4 HI(R), IP(RVS) | FQDN->HI |                   |
        | |                    | FQDN->IP |                   |
        | |                    +----------+                   |
        | |                                                   |
        | |                   #1 Update IP(R) in HI(R)->IP(R) |
        | |        +--------+    whenever IP(R) changes.      |
        | |        |  RVS   |<------------------------------+ |
        | |        |        |                               | |
        | V     +->| HI->IP |--+                            | |
      +-----+   |  +--------+  |                          +-----+
      |     |---+              +------------------------->|     |
      |  I  |    #5 First Message of HIP Base Exchange    |  R  |
      |     |                                             |     |
      |     |<--------------------------------------------|     |
      |     |-------------------------------------------->|     |
      |     |<--------------------------------------------|     |
      +-----+       #6 Remainder of HIP Base Exchange     +-----+

     Figure 3: HIP Lookup and Base Exchange with Rendezvous Server

   Figure 3 shows a HIP lookup and Base Exchange involving a Rendezvous
   Server.  Here, HIP node R is using Rendezvous Server RVS.  In step
   #1, it updates RVS with its current IP addresses IP(R).  Then, in
   step #2, R registers the Rendezvous Server's IP addresses IP(RVS) in
   its FQDN(R)->IP(RVS) DNS entry.

   In step #3, a second HIP node I issues a DNS lookup on FQDN(R) to
   obtain R's Host Identities HI(R) and IP addresses.  The lookup
   returns R's Host Identities HI(R) in step #4.  The DNS reply also
   includes the IP addresses of the Rendezvous Server IP(RVS) (instead
   of IP(R), because R's current addresses are unknown to the DNS.)

   In step #5, node I initiates the HIP Base Exchange.  It addresses the
   first packet of the HIP Base Exchange to IP(RVS).  Upon receipt, the
   Rendezvous Server relays the packet to one of R's current IP
   addresses IP(R).  The remainder of the HIP Base Exchange then occurs
   directly between I and R in step #6.

   When Rendezvous Servers maintain the HI->IP information, they may
   support more efficient update operations compared to dynamic DNS
   updates (Section 4.1).  Unlike the DNS, Rendezvous Servers do not
   provide a lookup service.  Instead, they use the HI->IP information
   to actively relay traffic between HIP nodes.

   This approach changes the role of the IP addresses stored in a DNS



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   entry.  Traditionally, nodes were directly reachable at the IP
   addresses listed in their DNS entry.  HIP Rendezvous Server change
   this basic property by replacing the IP addresses of their client
   nodes in the DNS with their own.  The IP addresses in a DNS entry
   hence no longer directly designate interfaces of an endpoint.
   Instead, they identify interfaces of a node that can relay packets to
   the endpoint.

5.  HIP Extensions for Rendezvous Servers

   The following sections describe HIP extensions for communication with
   Rendezvous Servers.  These extensions allow:

   o  A HIP Rendezvous Server to advertise its RVS capabilities to its
      correspondents.

   o  A HIP node to create a Rendezvous Association (RVA) with its
      Rendezvous Server, i.e., to register its current set of IP
      address(es).

   o  Two HIP nodes to establish a HIP Association (HA) between them via
      one or more Rendezvous Server.


5.1  Additional RVS_CAPABLE Control Field

   RVS mechanisms make use of a new Control Fields in the HIP Control
   Field: the RVS_CAPABLE Control Field.

   The RVS_CAPABLE Control Field ("R") allows a Rendezvous Server to
   advertise its rendezvous capabilities to the HIP nodes it associates
   with.

5.2  Additional HIP Parameters

5.2.1  RVA_REQUEST Parameter Format and Processing















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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Lifetime                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           RVA Type #1         |           RVA Type #2         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           RVA Type #n         |             padding           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type         100
   Length       Length in octets, excluding Type, Length and Padding
   Lifetime     This field encode, the desired RVA validity time.
   RVA Type     This field encode, in order of preference, the
                preferred rendezvous service types.




   The following RVA Types are defined:

   Type number  RVA Type
   -----------  --------
   0            Reserved by IANA
   1            I1_REWRITE_DST
   2            I1_REWRITE_SRCDST
   3            I1R1_REWRITE_SRCDST
   4            I1_RELAY_ESP
   5            I1R1_RELAY_ESP
   6            REDIRECT
   6-200        Reserved by IANA
   201-255      Reserved by IANA for private use

   When a Rendezvous Association of type I1_* is established between a
   HIP RVS and its peer, the RVS will relay to the peer all inbound I1s
   whose Responder HIT match those of the peer.  The peer will then
   reply with a R1 sent directly to the Initiator, without further
   assistance from the RVS.

   When a Rendezvous Association of type I1R1_* is established between a
   HIP RVS and its peer, the RVS will relay to the peer all inbound I1s
   whose Responder HIT match those of the peer.  The peer will then
   reply with a R1 sent to the Initiator via the RVS, which will relay
   it to the Initiator.  The Initiator will then reply directly to the
   Responder by sending an I2, without further assistance from the RVS.




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   A RVS relays packet by either rewriting IP addresses in the IP
   header, or alternatively, if a HIP association is present, by
   forwarding it into the ESP SA associated with the HIP Association.

   If the RVA is of type *_REWRITE_*, the IP addresses are rewritten by
   the RVS.  If the RVA type is I1_REWRITE_DST, only the destination IP
   address of a relayed I1 is rewritten.  On the contrary, if the RVA
   type *_REWRITE_SRCDST, both the source and destination IP addresses
   are rewritten.  In the case of a *_REWRITE_SRCDST, the RVS will need
   to suffix the HIP header with a FROM parameter preserving the
   original source IP address of the relayed packet.  This FROM, as well
   as the whole HIP header, is integrity protected by an RVA_HMAC
   parameter which contains a keyed-HMAC computed over the HIP packet,
   similarly to what the HMAC parameter already does.

5.2.2  RVA_REPLY Parameter Format and Processing


      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              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Lifetime                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           RVA Type #1         |           RVA Type #2         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           RVA Type #n         |             padding           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type         102
   Length       Length in octets, excluding Type, Length and Padding
   Lifetime     This field encode the offered RVA validity time
   RVA Type     This field encode, in order of preference, the
                preferred rendezvous service types (the same
                type values than RVA_REQUEST parameter are used).


5.2.3  RVA_HMAC Parameter Format and Processing

   The RVA_HMAC is an OPTIONAL parameter whose only difference with the
   HMAC parameter defined in [4] is the Type code:









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   Type         65320
   Length       20
   HMAC         160 low order bits of a HMAC keyed with the appropriate
                HIP integrity keys (HIP_lg or HIP_gl) of the corresponding
                Rendezvous Association or HIP Association. This HMAC is
                computed over the HIP packet excluding RVA_HMAC and any
                other following parameter. The checksum field MUST be set
                to zero and the HIP header length in the HIP common header
                MUST be calculated not to cover any excluded parameter when
                the Authenticator field is calculated.


   To allow a HIP node and any of its RVS to verify the integrity of
   packets flowing between them, both use an RVA_HMAC parameter keyed
   with a HMAC of HIP_lg and HIP_gl integrity keys.  One RVA_HMAC SHOULD
   be present on every packets flowing between a HIP node and any of its
   RVS and MUST be present when FROM and TO parameters are processed.

   On the receiving side, when an RVA_HMAC is validated, it SHOULD be
   removed from the packet and if so, packet length and checksum MUST be
   recomputed accordingly.

5.2.4  FROM Parameter Format and Processing

      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              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                             Address                           |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type         65100 (under signature) or 65300 (after signature)
   Length       16
   Address      An IPv6 address or an IPv4-in-IPv6 format IPv4 address


   A Rendezvous Server MAY add a FROM parameter containing the original
   source IP address of a HIP packet (I1, R1, I2 or R2) whose source IP
   address has been rewritten.  If one or more FROM parameters are
   already present, the new FROM parameter MUST be appended after the
   existing ones.  Each time an RVS inserts a FROM parameter, it MUST
   also insert additional parameters that will be used to validate this
   and the subsequent HIP packets.  These parameters are:




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   o  An ECHO_REQUEST, containing a chunk of opaque data allowing to
      validate, in a possible subsequent answer, a TO parameter which
      MUST be protected by an ECHO_RESPONSE containing the same opaque
      data.

   o  A valid RVA_HMAC, protecting the packet integrity.

   When a HIP node validates a FROM parameter, it is removed from the
   packet and recorded for later use (i.e., for building the
   corresponding TO parameter to be piggy-backed onto a subsequent
   answer).  The packet's source IP address is also replaced by the
   address included in the first occurrence of FROM parameter.

   For each FROM parameter, a HIP node MAY add to its replies a TO
   parameter containing the IP address included in the FROM.  These
   replies will be sent via the RVS, which MUST remove the outer TO
   parameter from the packet and replace its destination address with
   the address contained in the TO parameter before relaying it.

5.2.5  TO Parameter Format and Processing

      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              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                             Address                           |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type         65102 (under signature) or 65302 (after signature)
   Length       16
   Address      An IPv6 address or an IPv4-in-IPv6 format IPv4 address


   A HIP node MAY add one or more TO parameter containing the final
   destination IP address of a HIP packet (I1, R1, I2 or R2) whose
   destination IP address needs to be rewritten by an RVS.  This is
   essentially equivalent to loose source-routing.  If one or more TO
   parameters are already present, the new TO parameter MUST be appended
   after the existing ones.  Each time a node inserts a TO parameter, it
   MUST also insert additional parameters that will be used by the RVS
   for validation.  These parameters are:

   o  An ECHO_RESPONSE, containing a chunk of opaque data allowing the
      RVS to validate the address contained in the TO parameter.



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   o  A valid RVA_HMAC, protecting the packet integrity.

   When the RVS validates a TO parameter, SHALL remove it from the
   packet, and SHALL replace the packet destination IP address  with the
   address included in the TO parameter.  Packet length and checksum
   MUST then be recomputed accordingly.

   For each FROM parameter, a HIP node MAY add to its replies a TO
   parameter containing the IP address included in the FROM.  These
   replies will be sent via the RVS, which MUST remove the outer TO
   parameter from the packet and replace its destination address field
   with the address contained in the TO parameter before relaying it.

5.2.6  VIA_RVS Parameter Format and Processing

      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              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Address                            |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                               .                               .
     .                               .                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Address                            |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type           65500
   Length         Variable
   Address        An IPv6 address or an IPv4-in-IPv6 format IPv4 address


   At some point a, HIP endpoint might be in position to begin to send
   HIP packets directly towards the remote HIP endpoint's IP address,
   without further assistance from one or more of its RVS(s).  In that
   case, it MAY include in these packets a subset of the IP address(es)
   of its RVSs for debugging purposes.

   Similarly, a RVS relaying an I1 to the Responder or an R1 to the
   Initiator MAY include in these packets its IP address for debugging
   as well.



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   When the IP address of a RVS need to be included in a packet, by
   either an end-node or the RVS itself, one of these two methods is
   used:

   o  Add RVS IP address into an existing VIA_RVS parameter situated at
      the end of the HIP packet, while modifying accordingly the size of
      the parameter.

   o  Append a newly created VIA_RVS parameter at the end of the HIP
      packet if it does not already contain a VIA_RVS parameter.

   Note that the main goal of using the VIA_RVS parameter is to allow
   operators to diagnose possible issues encountered while establishing
   a HIP association via a RVS.

5.3  Use of Existing HIP Messages and Parameters

5.3.1  ECHO_REQUEST and ECHO_REPLY Parameters

   A FROM parameter MAY be augmented by including an ECHO_REQUEST
   parameter to the carrying packet.  The contents of the ECHO_REQUEST
   might then be echoed back in ECHO_RESPONSE.

   A TO parameter SHOULD be augmented and authenticated by including an
   ECHO_REPLY parameter to the carrying packet.  The contents of the
   ECHO_REPLY MUST be copied from a previously received ECHO_RESPONSE.

   All the HIP packets requiring RVS relaying facility to carry an
   answer packet SHOULD be augmented by the RVS with an ECHO_REQUEST
   parameter.

   A possible packet answered via the RVS, thus requiring relaying
   facility, SHOULD be authenticated by an ECHO_REPLY parameter.  The
   contents of the ECHO_REPLY MUST be copied from a previously received
   ECHO_RESPONSE.

   On the receiving side, when a HIP node validates an ECHO_REPLY
   located after the signatures, it MUST remove it from the packet and
   recompute packet length and checksum accordingly.

5.3.2  REA Parameter

   A HIP node associated via an RVS MAY use a REA parameter to make its
   correspondent aware of its veritable current IP address.  If used,
   the REA parameter MUST be used in conformance with the guidelines
   specified in [5].





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6.  Diagram Notation

   Notation     Significance
   --------     ------------

   I, R         I and R are the respective source and destination IP
                addresses of the IP header

   HIT-I,       HIT-I and HIT-R are respectively the Initiator and the
   HIT-R        Responder HIT of the packet

   R            The RVS_CAPABLE Control Field is set into the Control
                Field of the HIP header


   REA:I        A REA parameter containing the IP address i is
                present in the HIP header

   FROM:I       A FROM parameter containing the IP address I is present
                in the HIP header

   TO:I         A TO parameter containing the IP address I is present
                in the HIP header

   VIA:RVS              A VIA_RVS parameter containing IP addresses RVS
                is present in the HIP header

   REDIR:R              A REDIRECT parameter containing IP address R of
                Responder is present in the HIP header

   EREQ         An ECHO_REQUEST parameter is present in the HIP header

   EREP         An ECHO_REPLY parameter is present in the HIP header

   RREQ         A RVA_REQUEST parameter is present in the HIP header

   RREP         A RVA_REPLY parameter is present in the HIP header



7.  Establishing Rendezvous Associations

   A HIP node that wants to register its IP address with its RVS MAY
   simply establish a HIP association with it.  It MUST then keep its IP
   address current with the server by sending UPDATE packets whenever
   its set of IP addresses changes.

   However, for the sake of economizing RVS resources, which can



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   possibly be used by several thousands of different HIP nodes, we
   define a new sort of "soft state" HIP association called a Rendezvous
   Association (RVA).  In order to maintain this RVA established, a HIP
   Association need not remain established.

   A HIP node MAY establish an RVA with its RVS by establishing a HA
   while adding an RVA_REQUEST parameter in an I2, possibly preceded by
   an I1 containing the same RVA_REQUEST.  The possibility offered to
   initiate the protocol in I1 allows a HIP node to query a RVS for the
   set of offered rendezvous service types before completing the
   establishment of the Rendezvous association (in case the desired
   service type isn't available on this RVS).  A RVS MUST then reply
   with, respectively, an R2 possibly preceded by an R1, which will both
   have the RVS_CAPABLE control field set, and contain a RVA_REPLY
   parameter specifying the characteristics of the offered RVA (validity
   time, type, etc.).  Then, the RVS and the HIP node MAY delete most of
   the HIP Association state, retaining only the Lifetime, Initiator's
   HIT and IP address(es), as well as HIP_lg and HIP_gl integrity keys.

   When a HA is established via an RVS, the integrity of HIP packets
   flowing between a HIP node and its RVS is protected by an additional
   RVA_HMAC keyed with these keys.





























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                      I1(I, RVS, HIT-I,
                         HIT-RVS)           +------+
                +-------------------------->|      |
                |+--------------------------|      |
                ||    R1(RVS, I, HIT-RVS,   |      |
                ||       HIT-I, R)          |      |
                ||                          | RVS1 |
                ||     I2(I, RVS, HIT-I,    |      |
                ||        HIT-RVS, RREQ)    |      |
                || +----------------------->|      |
                || |+-----------------------|      |
                || ||  R2(RVS, I, HIT-RVS,  +------+
                || ||     HIT-I, R, RREP)
                |V |V
               +-----+
               |     |
               |  I  |
               |     |
               +-----+

            Figure 12: Establishing a Rendezvous Association

   There is nothing to prevent an RVS node to advertise its RVS
   capabilities to the peers it associates with, nor to establish an RVA
   with another RVS.

   If a HIP node wants to associate with several cascaded Rendezvous
   Servers RVS_i (0 < i < n+1), it SHALL sequentially create RVAs
   (RVA_i) with each of them, starting from the "nearest" (RVS_1) to the
   "farthest" (RVS_n).  Apart from RVA_1, a node SHOULD create any such
   RVA_i (1 < i < n+1) by sending an I1 to RVS_i via each of the RVS
   which precede it, i.e., RVS_j (1 < j < i).

   This is achieved by using (i - 1) different TO parameters containing,
   in order, the IP address of each RVS preceding RVS_i, i.e., RVS_j (1
   < j < i).  This process is similar to IP loose source-routing.
   Hence, A RVS accepting to be part of a cascade MAY relay an incoming
   I1 from one its clients to any given address and HIT.  Those I1s MUST
   be protected by a valid RVA_HMAC parameter.












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         I1(I, RVS1, HIT-I,                  I1(RVS1, RVS2, HIT-I,
         HIT-RVS2, TO:RVS2)      +------+       HIT-RVS2, EREQ1)
     +-------------------------->|      |----------------------------+
     |+--------------------------|      |<--------------------------+|
     || R1(RVS1, I, HIT-RVS2,    |      |   R1(RVS2, RVS1,          ||
     ||    HIT-I, R, EREQ1)      |      |      HIT-RVS2, HIT-I,     ||
     ||                          | RVS1 |      R, EREP1)            ||
     ||   I2(I, RVS1, HIT-I,     |      |                           ||
     ||      HIT-RVS2, RREQ,     |      | I2(RVS1, RVS2, HIT-I,     ||
     ||      EREP1, TO:RVS2)     |      |    HIT-RVS2, RREQ, EREQ1) ||
     || +----------------------->|      |------------------------+  ||
     || |+-----------------------|      |<----------------------+|  ||
     || || R2(RVS1, I, HIT-RVS2, +------+  R2(RVS2, RVS1,       ||  ||
     || ||    HIT-I, R, RREP,                 HIT-RVS2, HIT-I,  ||  ||
     || ||    EREQ1)                          R, RREP, EREP1)   ||  ||
     |V |V                                                      |V  |V
    +-----+                                                    +------+
    |     |                                                    |      |
    |  I  |                                                    | RVS2 |
    |     |                                                    |      |
    +-----+                                                    +------+

        Figure 13: Establishing Cascaded Rendezvous Associations


8.  Establishing HIP Associations via Rendezvous Servers

8.1  Sending a Redirect in Reply to I1

   Instead of having the RVS relay incoming I1s to the correct
   Responder, one possibility is to answer with a REDIRECT packet when a
   HIP packet destined for one of the Rendezvous Server's HIP nodes
   arrives.  This REDIRECT packet would contains the IP address and
   packet signature of the Responder.

   The Responder cannot sign the redirect packets delivered by the RVS
   in real time.  When the RVA is set up, the Responder sends the signed
   REDIRECT packet to the RVS, who stores it until the RVA expires.

   By signing this REDIRECT packet and sending it to the RVS, the
   Responder is authorizing the Rendezvous Server's IP address to
   redirect Initiators to the Responder's IP address.  The authorization
   is weak because the subject of the authorization is the IP address
   which is not bound to the HI of the Responder (similarly to what is
   described in , the possibility to use CGAs as IP addresses for RVSs
   might improve authorization security because the RVS might then prove
   to Initiators ownership of the CGA IP address, and the authorization
   issued to it to redirect to the Responder's IP address.



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   An implementation of this redirect packet is a R1 packet signed by
   the Responder, which contains an additional REDIRECT parameter (with
   the IP address of the Responder, and perhaps a limitation of the
   REDIRECT validity, like 'not-before' and 'not-after' dates, or hash
   chains) The RVS redirect an Initiator by replying to an I1 with this
   REDIRECT R1 in which the receiver HIT field has been field with the
   HIT of the Initiator.  Note that this may expose the Initiator to
   replay attacks, but this is not very different from the situation
   where the Initiator receives a signed R1 whose signature also omits
   Receiver HIT.

                                           _____OFFLINE______
                                           R1(R, RVS, HIT-R
    I1(I, RVS, HIT-I, HIT-R) +---------+      HIT-0, REDIR:R)
    +------------------------|         |
    |                        |   RVS   |<-+-+-+-+-+-+-+-+-+-+
    |  +---------------------|         |                    |
    |  | R1(RVS, I, HIT-R,   +---------+                    +
    |  V    HIT-I, REDIR:RVS->R)                            |
   +-----+            I1(I, R, HIT-I, HIT-R)            +-----+
   |     |--------------------------------------------->|     |
   |     |<---------------------------------------------|     |
   |  I  |            R1(R, I, HIT-R, HIT-I)            |  R  |
   |     |            I2(I, R, HIT-I, HIT-R)            |     |
   |     |--------------------------------------------->|     |
   |     |<---------------------------------------------|     |
   +-----+            R2(R, I, HIT-R, HIT-I)            +-----+

      Figure 14: Initiator redirected by Rendezvous Server with a
                          Responder-signed R1


8.2  Passing I1 onto an ESP SA

   If a HIP node and one of its Rendezvous Servers maintain a HIP
   Association, the Rendezvous Server MAY tunnel I1s incoming to this
   node's HIT into the corresponding ESP SA.  The main drawbacks of this
   approach are that, (1) middle-boxes cannot see the encrypted I1
   passing from an RVS to its clients, and (2) the source IP address of
   I1 is lost.  In particular, (2) implies that the RVS MUST transmit to
   the Responder the original source IP address by either of the
   following:

   o  add a FROM parameter to the HIP header

   o  include the whole original IP header in the ESP payload (very
      similar to ESP tunnel mode)




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   o  route back the subsequent R1 via the RVS


                                       ESP(RVS, R,
                                           I1(I, RVS, HIT-I,
    I1(I, RVS, HIT-I, HIT-R) +---------+      HIT-R, FROM:I))
    +----------------------->|         |--------------------+
    |                        |   RVS   |                    |
    |                        |         |                    |
    |                        +---------+                    |
    |                                                       V
   +-----+    R1(R, I, HIT-R, HIT-I, REA:R, VIA:RVS)    +-----+
   |     |<---------------------------------------------|     |
   |     |                                              |     |
   |  I  |            I2(I, R, HIT-I, HIT-R)            |  R  |
   |     |--------------------------------------------->|     |
   |     |<---------------------------------------------|     |
   +-----+             R2(R, I, HIT-R, HIT-I)           +-----+

       Figure 15: Rendezvous Server Forwarding I1 onto an ESP SA


8.3  Rewriting I1 Destination IP Address

   When a HIP packet destined for one of its HIP nodes arrives at a
   Rendezvous Server, it relays the packet to one of the HIP node's
   current IP addresses.  In most case, it is expected that only the
   first packet of a HIP Base Exchange (i.e., I1) will require such
   relaying [2].  Subsequent packet of the HIP Base Exchange and all
   further data packets will directly flow between the HIP nodes,
   bypassing the Rendezvous Server.  The RVA established between such a
   RVS and its peer has type I1_REWRITE_DST.

   In the simplest case, the Rendezvous Server can relay an I1 towards
   its true destination by merely replacing the destination IP address
   of the I1 by one of the destination HIT owner's IP address(es).
   Note, however, that such I1s might be subject to egress filtering on
   the Rendezvous Server's network [9], thus causing I1 packet to be
   dropped (source IP address does not belong to the RVS network).












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                                         I1(I, R, HIT-I,
    I1(I, RVS, HIT-I, HIT-R) +---------+    HIT-R, FROM:I)
    +----------------------->|         |--------------------+
    |                        |   RVS   |                    |
    |                        |         |                    |
    |                        +---------+                    |
    |                                                       V
   +-----+    R1(R, I, HIT-R, HIT-I, REA:R, VIA:RVS)    +-----+
   |     |<---------------------------------------------|     |
   |     |                                              |     |
   |  I  |            I2(I, R, HIT-I, HIT-R)            |  R  |
   |     |--------------------------------------------->|     |
   |     |<---------------------------------------------|     |
   +-----+             R2(R, I, HIT-R, HIT-I)           +-----+

    Figure 16: Rendezvous Server Rewriting I1 Destination IP Address


8.4  Rewriting I1 Source and Destination IP Addresses

   Because of egress filtering, a HIP Rendezvous Server might need to
   replace the original source IP address of an I1 by its own IP
   address, thus concealing the Initiator's IP address to the Responder.

   While this might be desirable, one of the extension described in this
   document allows a Rendezvous Server to piggy-back incoming HIP
   packets with an OPTIONAL FROM parameter containing the original
   source IP address of the packet.  A HIP node receiving a packet
   containing such a FROM parameter has two possibilities for answering
   back.  It might answer an R1 back either:

   o  Directly to the IP address included in the FROM parameter.  The
      RVA established between such a RVS and its peer has type
      I1_REWRITE_SRCDST.

   o  Via the Rendezvous Server IP address, adding to the R1 HIP header
      a TO parameter containing the IP address included in the FROM
      parameter.  The RVA established between such a RVS and its peer
      has type I1R1_REWRITE_SRCDST.












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                                             I1(I, RVS, HIT-I,
       I1(I, RVS, HIT-I, HIT-R) +---------+     HIT-R, FROM:I, VIA:RVS)
       +----------------------->|         |--------------------+
       |                        |   RVS   |                    |
       |                        |         |                    |
       |                        +---------+                    |
       |                                                       V
      +-----+     R1(R, I, HIT-R, HIT-I, REA:R, VIA:RVS)   +-----+
      |     |<---------------------------------------------|     |
      |     |                                              |     |
      |  I  |            I2(I, R, HIT-I, HIT-R)            |  R  |
      |     |--------------------------------------------->|     |
      |     |<---------------------------------------------|     |
      +-----+             R2(R, I, HIT-R, HIT-I)           +-----+

  Figure 17: I1_REWRITE_SRCDST: Rendezvous Server Rewriting I1 Source
                      and Destination IP Addresses


8.5  Rewriting I1 and R1 Source and Destination IP Addresses

   It might be useful to relay further HIP packets (i.e., R1) via the
   RVS.  For example, if the Initiator does not know the Responder's
   HIT, it will initiate an opportunistic exchange with the Responder
   via a RVS.  The first problem  is for the RVS to forward an I1 which
   doesn't have a destination HIT to the correct Responder.

   Because an opportunistic Initiator uses the unspecified IPv6 address
   (i.e., ::0) as a place-holder for the Responder HIT in I1s it sends,
   an RVS cannot use this Responder HIT to demultiplex incoming
   "opportunistic" I1s.  The only way to properly relay such
   Opportunistic I1s is for the RVS to lease per-HIT IP addresses, so
   the destination IP addresses of Opportunistic I1s can be used as a
   key to find the correct Responder.

   In order to avoid trivial spoofing attacks with R1s, a HIP node
   receiving an opportunistic I1 from a Rendezvous Server MUST reply
   with its R1 via the same Rendezvous Server.  Accordingly, an
   Initiator who has attempted an opportunistic exchange towards an IP
   address (those of the RVS) MUST discards all R1s received in answers
   which do not come from the same IP address.  When sending the R1 via
   the RVS, the Responder MUST initiate the readdressing protocol as
   described in [5].

   This restriction is made for security reasons.  If the Initiator
   receives an R1 directly from the Responder, the only way to find the
   appropriate HIP state is to use as a key the RVS's IP address, which
   is possibly included in a VIA_RVS parameter.  This solution MUST be



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   avoided because the VIA_RVS parameter is not trusted (The Initiator
   doesn't have a priori knowledge of the public key, and the included
   RVS IP address hasn't been "validated" by having the routing fabric
   delivers the IP header with this address as source).  If this
   restriction is not made, a passive attacker might easily hijack a HIP
   state in I1_SENT state: it would learn a (source,destination) tuple
   of IP addresses in a flowing I1, then send to the source address a
   self-made R1 with a VIA_RVS parameter containing the destination
   address; that's it, the attacker hijacked the I1_SENT state.  This an
   opportunity for eavesdropping, MitM, as well as DoS attacks.

   Because these R1 packets are larger than I1 (they contain public keys
   and signatures), the relaying of such packet create an opportunity
   for denial of service attacks.  To defend against these attacks, the
   Rendezvous Server needs to differentiate between legitimate HIP
   packets (i.e., I1 and subsequent HIP packets triggered by an I1) and
   illegitimate ones.

   For the sake of reducing the load incurred on the RVS, an RVS is not
   required to keep track of IP addresses and other pieces of state
   associated with ongoing HIP exchanges.  Such behavior is OPTIONAL.
   Instead, the relaying facility MAY make use of ECHO_REQUEST and
   ECHO_RESPONSE parameters.

   Each time a packet is being relayed, the RVS MAY augment it with an
   ECHO_REQUEST parameter containing a chunk of opaque data.  The
   receiver of such a packet SHOULD augment any packet answering to this
   packet with an ECHO_REPLY parameter containing the same chunk of
   opaque data.  This opaque data allows an RVS to find and validate the
   answered packet IP addresses and HITs.  When successfully validated,
   ECHO_REPLY parameters SHOULD be removed from the packet before
   relaying.



















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       I1(I, RVS,                    I1(RVS, R, HIT-I, HIT-0
          HIT-I, HIT-0)   +---------+   FROM:I, EREQ)
    +-------------------->|         |----------------------+
    |+--------------------|         |<--------------------+|
    || R1(RVS, I, HIT-R,  |   RVS   | R1(R, RVS, HIT-R,   ||
    ||    HIT-I, REA:R,   |         |    HIT-I, REA:R,    ||
    ||    VIA:RVS)        |         |    TO:I, EREP)      ||
    ||                    |         |                     ||
    ||                    +---------+                     ||
    |V                                                    |V
   +-----+             I2(R, I, HIT-R, HIT-I)          +-----+
   |     |-------------------------------------------->|     |
   |     |<--------------------------------------------|     |
   |     |             R2(I, R, HIT-I, HIT-R)          |     |
   |  I  |                                             |  R  |
   |     |              ESP(R, I, SPI-R)               |     |
   |     |<--------------------------------------------|     |
   |     |-------------------------------------------->|     |
   +-----+              ESP(I, R, SPI-I)               +-----+


  Figure 18: I1R1_REWRITE_SRCDST: Responder replying via the RVS to an
                        Opportunistic Initiator


8.6  Cascading Rendezvous Servers

   In some situations, it might be useful to use cascaded Rendezvous
   Servers to establish RVS associations.  A typical scenario would be a
   small number of "trusted" Rendezvous Servers and a larger number of
   "untrusted" Rendezvous Servers.  Only the trusted Rendezvous Servers
   are aware of the IP addresses of the Responders.  The untrusted
   servers know only the IP addresses of other (un)trusted Rendezvous
   Servers.  Untrusted Rendezvous Servers are changed periodically, in
   order to lower the opportunity for flooding-type attacks on their IP
   addresses.

   In the case of cascaded Rendezvous Servers, the parameters added to
   the HIP base exchange, like FROM, TO, VIA_RVS, ECHO_REQUEST/REPLY or
   RVA_HMAC, MUST be "aggregated" or "clustered" on a per-type basis.
   This means that, when an RVS needs to add onto a HIP packet a
   parameter which is already present in it, this parameter MUST be
   added just after the existing parameter(s) of the same type.  For
   instance, a FROM parameter MUST be added just after the existing
   FROM(s) parameter(s).  The same applies to  TO, VIA_RVS,
   ECHO_REQUEST/REPLY or RVA_HMAC.

   Another solution to cascaded Rendezvous Servers may be to encapsulate



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   the original packet into a PAYLOAD and then piggy-back it with
   additional parameters.  This scheme has not been evaluated further.

                                                 I1(RVS2, R, HIT-I,
     I1(I, RVS,         I1(RVS1, RVS2,              HIT-R, EREQ1,
        HIT-I,             HIT-I, HIT-R,            EREQ2, FROM:I,
        HIT-R) +------+    EREQ1, FROM:I)  +------+ FROM:RVS1)
    +--------->|      |------------------->|      |---------+
    |          | RVS1 |                    | RVS2 |         |
    | +--------|      |<-------------------|      |<------+ |
    | |        +------+  R1(RVS2, RVS2,    +------+       | |
    | |                     HIT-I, HIT-R,                 | |
    | |                     EREP1, EREQ2,                 | |
    | |                     TO:I)                         | |
    | | R1(RVS1, I, HIT-R,             R1(R, RVS2, HIT-R, | |
    | |    HIT-I, REA:R,                  HIT-I, REA:R,   | |
    | |    EREQ2, EREQ1)                  EREP1, EREP2,   | |
    | |                                   TO:I, TO:RVS2)  | |
    | V                                                   | V
   +-----+    I2(I, R, HIT-I, HIT-R, EREP2, EREP1)     +-----+
   |     |-------------------------------------------->|     |
   |  I  |<--------------------------------------------|  R  |
   +-----+           R2(R, I, HIT-R, HIT-I)            +-----+

  Figure 19: Two Cascaded Rendezvous Servers Relaying an I1-R1 Message
                                  Pair


8.7  Implication on the HIP integrity checks

   The establishment of HIP associations via one or more Rendezvous
   Servers causes HIP packets flowing between the HIP nodes to be
   modified during transmission.  Several kinds of modifications to both
   the IP and HIP headers are possible.  The HIP protocol uses two kinds
   of packet integrity checks: hop-by-hop and end-to-end.  The HIP
   checksum is a hop-by-hop check and SHOULD be verified and recomputed
   by each of the on-path HIP middle-boxes (e.g., Rendezvous Servers).
   The HMAC and SIGNATURE are end-to-end checks and MUST be computed by
   the sender and verified by the receiver.

8.7.1  Checksum

   The checksum field of a HIP header to be modified MUST be verified
   before applying the modification and recomputed accordingly after.

8.7.2  HMAC and SIGNATURE

   The HMAC and SIGNATURE field of a HIP header MUST be computed and



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   verified based on a "sender view" or "receiver view" of the HIP
   header.  In particular, this implies that SIGNATURE and HMAC MUST NOT
   cover FROM and TO parameters added or removed by Rendezvous Servers
   and that the HIP pseudo-header used to compute and verify them MUST
   contain the IP addresses as seen by the remote HIP peer.  In case of
   IP address concealment by the RVS, this means that the IP address of
   this RVS MUST be used in the pseudo-header in place of the IP address
   of the end host it conceals.

8.7.3  Example

   Here is an example showing how to compute the different integrity
   checks (end-to-end and hop-by-hop) when two Rendezvous Servers are
   cascaded and conceals the Responder IP address (packet flowing along
   the path I -> RVS1 -> RVS2 -> R)

   End-to-end integrity checks: HMAC and SIGNATURE are computed with a
   pseudo-header containing RVS1 as a place holder for the destination
   IP address, the rationale being that RVS1 is concealing the Responder
   IP address.  Therefore, R will verify the signature using RVS1 as the
   destination IP address in the pseudo-header.

   Hop-by-hop integrity checks: Checksum is computed hop-by-hop; first
   with I and RVS1, then with RVS1 and RVS2, and finally with RVS2 and
   R.

9.  Security Considerations

   The security aspects of different HIP rendezvous mechanisms are
   currently being investigated.  This section describes the known
   threats introduced by these HIP extensions, and implications on the
   overall security of HIP and IP.  In particular, the following tries
   to show that the extensions described in this document do not
   introduce additional threats in the Internet infrastructure.

   It is difficult to encompass the whole scope of threats introduced by
   Rendezvous Servers because their presence have implications both at
   the IP and HIP layer.  In particular, the extensions hereby described
   might allow for redirection, amplification and reflection attacks at
   the IP layer, as well as attacks on the HIP layer itself, for example
   Man-in-the-Middle attacks against the cryptographic core-protocol
   SIGMA used by HIP.

   If an Initiator has an a priori knowledge of the Responder's HI when
   it first contacts it via the RVS, it has a means to verify the
   signatures in the HIP exchange, thus conforming to the SIGMA protocol
   which is resilient to Man-in-the-Middle attacks.




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   If an Initiator has not an a priori knowledge of the Responder's HI
   (so called Opportunistic Initiators), it is almost impossible to
   defend the HIP exchange against MitM attacks (cannot authenticate
   public keys exchanged).  The only solution is to mitigate hijacking
   threats on the HIP state by requiring an R1 answering an
   Opportunistic I1 to come from the IP address where the I1 was
   initially sent.  That way we retain a level of security which is
   equivalent to what exists today in the Internet: By sending an IP
   packet to an IP address, and receiving an answered IP packet from
   this same IP address, I know that the routing fabric trusts my
   correspondent to be represented by this IP address.  While it is true
   that such security is weak, it is better than none, and avoids to
   introduce additional threats at the IP layer.

10.  IANA Considerations

   IANA needs to open a new registry for the Rendezvous Association
   (RVA) type.  Defined RVA types are:

      Type number       RVA Type

      -----------       --------

      0         Reserved by IANA

      1         I1_REWRITE_DST

      2         I1_REWRITE_SRCDST

      3         I1R1_REWRITE_SRCDST

      4         I1_RELAY_ESP

      5         I1R1_RELAY_ESP

      6         REDIRECT

      6-200     Reserved by IANA

      201-255   Reserved by IANA for private use

   Adding new reservations requires IETF consensus RFC2434 [14].

11.  Acknowledgments

   The following people have provided thoughtful and helpful discussions
   and/or suggestions that have improved this document: Marcus Brunner,
   Tom Henderson, Miika Komu, Mika Kousa, Pekka Nikander, Simon Schuetz,



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   Tim Shepard, Kristian Slavov, Martin Stiemerling, and Juergen
   Quittek.

   Part of this work is a product of the Ambient Networks project,
   partially supported by the European Commission under its Sixth
   Framework Programme.  It is provided "as is" and without any express
   or implied warranties, including, without limitation, the implied
   warranties of fitness for a particular purpose.  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.

12.  References

12.1  Normative References

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

   [2]   Moskowitz, R. and P. Nikander, "Host Identity Protocol
         Architecture", draft-ietf-hip-arch-00 (work in progress),
         October 2004.

   [3]   Nikander, P. and J. Laganier, "Host Identity Protocol (HIP)
         Domain Name System (DNS) Extensions", draft-ietf-hip-rvs-00
         (work in progress), October 2004.

   [4]   Moskowitz, R., Nikander, P. and P. Jokela, "Host Identity
         Protocol", draft-ietf-hip-base-01 (work in progress), October
         2004.

   [5]   Nikander, P., "End-Host Mobility and Multi-Homing with Host
         Identity Protocol", draft-ietf-hip-mm-00 (work in progress),
         October 2004.

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

   [7]   Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
         Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
         April 1997.

   [8]   Wellington, B., "Secure Domain Name System (DNS) Dynamic
         Update", RFC 3007, November 2000.

   [9]   Killalea, T., "Recommended Internet Service Provider Security
         Services and Procedures", BCP 46, RFC 3013, November 2000.



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   [10]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
         Defeating Denial of Service Attacks which employ IP Source
         Address Spoofing", BCP 38, RFC 2827, May 2000.

12.2  Informative References

   [11]  Saltzer, J., "On the Naming and Binding of Network
         Destinations", RFC 1498, August 1993.

   [12]  Kent, S. and R. Atkinson, "Security Architecture for the
         Internet Protocol", RFC 2401, November 1998.

   [13]  Klensin, J., "Role of the Domain Name System (DNS)", RFC 3467,
         February 2003.

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

   [15]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on
         Security Considerations", BCP 72, RFC 3552, July 2003.


Authors' Addresses

   Julien Laganier
   Sun Labs (Sun Microsystems) & LIP (CNRS/INRIA/ENSL/UCBL)
   180, Avenue de l'Europe
   Saint Ismier CEDEX  38334
   FR

   Phone: +33 476 188 815
   EMail: ju@sun.com
   URI:   http://research.sun.com/


   Lars Eggert
   NEC Network Laboratories
   Kurfuersten-Anlage 36
   Heidelberg  69115
   DE

   Phone: +49 6221 90511 43
   Fax:   +49 6221 90511 55
   EMail: lars.eggert@netlab.nec.de
   URI:   http://www.netlab.nec.de/





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Appendix A.  Document Revision History

   +-----------+-------------------------------------------------------+
   | Revision  | Comments                                              |
   +-----------+-------------------------------------------------------+
   | 00        | Compared to draft-eggert-hip-rvs-00: Add              |
   |           | 'Terminology' section. Remove sections about privacy  |
   |           | (goes into the HIP RG RVS draft). Wrote 'Security     |
   |           | Considerations' and 'IANA Considerations' sections.   |
   |           | Add I1/R1 relaying to support Opportunistic           |
   |           | Initiators. Complete REDIRECT packet description.     |
   |           | Compared to draft-eggert-hip-rendezvous-00: Minor     |
   |           | fixes to figures and their descriptive text. Added    |
   |           | RVS protocol specification. Removed sections related  |
   |           | to communications between HIP and non-HIP nodes. Use  |
   |           | boilerplate from RFC 3668.                            |
   +-----------+-------------------------------------------------------+


































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