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Versions: 00 01 draft-ietf-hip-native-nat-traversal

HIP Working Group                                             A. Keranen
Internet-Draft                                                  J. Melen
Intended status: Experimental                                   Ericsson
Expires: October 11, 2010                                  April 9, 2010


        Native NAT Traversal Mode for the Host Identity Protocol
               draft-keranen-hip-native-nat-traversal-01

Abstract

   This document specifies a new Network Address Translator (NAT)
   traversal mode for the Host Identity Protocol (HIP).  The new mode is
   based on the Interactive Connectivity Establishment (ICE) methodology
   and UDP encapsulation of data and signaling traffic.  The main
   difference from the previously specified modes is the use of HIP
   messages for all NAT traversal procedures.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   The list of current Internet-Drafts can be accessed at
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   This Internet-Draft will expire on October 11, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Protocol Description . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Relay Registration . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Registration Authentication  . . . . . . . . . . . . . . .  4
     3.3.  Forwarding Rules and Permissions . . . . . . . . . . . . .  5
     3.4.  Relaying UDP Encapsulated Data and Control Packets . . . .  6
     3.5.  Candidate Gathering  . . . . . . . . . . . . . . . . . . .  7
     3.6.  Base Exchange via HIP Relay Server . . . . . . . . . . . .  7
     3.7.  Native NAT Traversal Mode Negotiation  . . . . . . . . . .  7
     3.8.  Connectivity Check Pacing Negotiation  . . . . . . . . . .  7
     3.9.  Connectivity Checks  . . . . . . . . . . . . . . . . . . .  8
     3.10. NAT Keepalives . . . . . . . . . . . . . . . . . . . . . .  8
     3.11. Handling Conflicting SPI Values  . . . . . . . . . . . . .  9
   4.  Packet Formats . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  RELAYED_ADDRESS and MAPPED_ADDRESS Parameters  . . . . . .  9
     4.2.  PEER_PERMISSION Parameter  . . . . . . . . . . . . . . . . 10
     4.3.  HIP Connectivity Check Packets . . . . . . . . . . . . . . 11
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14















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1.  Introduction

   The Host Identity Protocol (HIP) [RFC5201] is specified to run
   directly on top of IPv4 or IPv6.  However, many middleboxes found in
   the Internet, such as NATs and firewalls, often allow only UDP or TCP
   traffic to pass [RFC5207].  Also, especially NATs usually require the
   host behind a NAT to create a forwarding state in the NAT before
   other hosts outside of the NAT can contact the host behind the NAT.
   To overcome this problem, different methods, commonly referred to as
   NAT traversal techniques, have been developed.

   Two NAT traversal techniques for HIP are specified in
   [I-D.ietf-hip-nat-traversal].  One of them uses only UDP
   encapsulation, while the other uses also the Interactive Connectivity
   Establishment (ICE) [I-D.ietf-mmusic-ice] protocol, which in turn
   uses Session Traversal Utilities for NAT (STUN) [RFC5389] and
   Traversal Using Relays around NAT (TURN) [I-D.ietf-behave-turn]
   protocols to achieve a reliable NAT traversal solution.

   The benefit of using ICE and STUN/TURN is that one can re-use the NAT
   traversal infrastructure already available in the Internet, such as
   STUN and TURN servers.  Also, some middleboxes may be STUN-aware and
   could be able to do something "smart" when they see STUN being used
   for NAT traversal.  However, implementing a full ICE/STUN/TURN
   protocol stack results in a considerable amount of effort and code
   which could be avoided by re-using and extending HIP messages and
   state machines for the same purpose.  Thus, this document specifies a
   new NAT traversal mode that uses HIP messages instead of STUN for the
   connectivity checks, keepalives, and data relaying.


2.  Terminology

   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 [RFC2119].

   This document uses the same terminology as
   [I-D.ietf-hip-nat-traversal] and the following:

   HIP data relay:
      A host that forwards HIP data packets, such as Encapsulating
      Security Payload (ESP) [RFC5202], between two hosts.








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   Registered host:
      A host that has registered for a relaying service with a HIP data
      relay.



3.  Protocol Description

   This section describes the normative behavior of the protocol
   extension.  Most of the procedures are similar to what is defined in
   [I-D.ietf-hip-nat-traversal] but with different, or additional,
   parameter types and values.  In addition, a new type of relaying
   server, HIP data relay, is specified.

3.1.  Relay Registration

   Relay registration procedure for HIP signaling is identical to the
   one specified in Section 4.1 of [I-D.ietf-hip-nat-traversal].
   However, a host MAY also register for UDP encapsulated ESP relaying
   using Registration Type value RELAY_UDP_ESP (value 3).

   If the HIP relay server supports relaying of UDP encapsulated ESP,
   the host is allowed to register for data relaying service (see
   Section 3.2), and the relay has relaying resources (free port
   numbers, bandwidth, etc.) available, the relay opens a UDP port on
   one of its addresses and signals the address and port to the
   registering host using the RELAYED_ADDRESS parameter (see Section 4.1
   for details).  If the relay would accept the data relaying request
   but does not have enough resources to provide data relaying service,
   it MUST reject the request with Failure Type 2 (Insufficient
   resources).

   The registered host MUST maintain an active HIP association with the
   data relay as long as it requires the data relaying service.  When
   the HIP association is closed (or times out), or the registration
   lifetime passes without the registered host refreshing the
   registration, the data relay MUST stop relaying packets for that host
   and close the corresponding UDP port.

   The data relay MAY use the same relayed address and port for multiple
   registered hosts, but since this can cause problems with stateful
   firewalls (see Section 5) it is NOT RECOMMENDED.

3.2.  Registration Authentication

   If the HIP data relay knows the Host Identities (HIs) of all the
   hosts that are allowed to use the relaying service, it SHOULD reject
   registrations from unknown hosts.  However, since it may be



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   unfeasible to pre-configure the relay with all the HIs, the relay
   SHOULD also support HIP certificates [I-D.ietf-hip-cert] to allow for
   certificate based authentication.

   When a host wants to register with a HIP data relay, it SHOULD check
   if it has a suitable certificate for authenticating with the relay.
   How the suitability is determined and how the certificates are
   obtained is out of scope for this document.  If the host has one or
   more suitable certificates, the host SHOULD include them (or just the
   most suitable one) in a CERT parameter to the HIP packet along with
   the REG_REQUEST parameter.  If the host does not have any suitable
   certificates, it SHOULD send the registration request without the
   CERT parameter to test whether the relay accepts the request based on
   the host's identity.

   When a relay receives a HIP packet with a REG_REQUEST parameter, and
   it requires authentication for at least one of the Registration Types
   listed in the REG_REQUEST parameter, it MUST first check whether the
   HI of the registering host is in the allowed list for all the
   Registration Types in the REG_REQUEST parameter.  If the host is in
   the allowed list (or the relay does not require any authentication),
   the relay MUST proceed with the registration.

   If the host was not in the allowed list and the relay requires hosts
   to authenticate, the relay MUST check whether the packet also
   contains a CERT parameter.  If the packet does not contain a CERT
   parameter, the server MUST reject the registrations requiring
   authentication with Failure Type 0 (Registration requires additional
   credentials) [RFC5203].  If the certificate is valid and accepted
   (issued for the registering host and signed by a trusted issuer), the
   relay MUST proceed with the registration.  If the certificate in the
   parameter is not accepted, the relay MUST reject the corresponding
   registrations with Failure Type 3 (Invalid certificate).

3.3.  Forwarding Rules and Permissions

   The HIP data relay uses a similar permission model as a TURN server:
   before any ESP data packets sent by a peer are forwarded, a
   permission must be set for the peer's address.  The permissions also
   install a forwarding rule, similar to TURN's channels, based on the
   Security Parameter Index (SPI) values in the ESP packets.

   Permissions are not required for the connectivity checks, but if a
   relayed address is selected to be used for data, the registered host
   MUST send an UPDATE message with a PEER_PERMISSION parameter with the
   address of the peer and the outbound and inbound SPI values the host
   is using with this peer.




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   When a data relay receives an UPDATE with a PEER_PERMISSION
   parameter, it MUST check if the sender of the UPDATE is registered
   for data relaying service, and drop the UPDATE if the host was not
   registered.  If the host was registered, the relay checks if there is
   a permission with matching information (address, protocol, port and
   SPI values).  If there is no such permission, a new permission is
   created and its lifetime is set to 5 minutes.  If an identical
   permission already existed, it is refreshed by setting the lifetime
   to 5 minutes.  A registered host SHOULD refresh permissions roughly 1
   minute before the expiration if the permission is still needed.

3.4.  Relaying UDP Encapsulated Data and Control Packets

   When a HIP data relay accepts to relay UDP encapsulated data, it
   opens a UDP port (relayed address) for this purpose as described in
   Section 3.1.  If the data relay receives a UDP encapsulated HIP
   control packet on that port, it MUST forward the packet to the
   registered host and add a RELAY_FROM parameter to the packet as if
   the data relay was acting as a HIP relay server
   [I-D.ietf-hip-nat-traversal].

   When a host wants to send a HIP control packet (such as a
   connectivity check packet) to a peer via the data relay, it MUST add
   a RELAY_TO parameter containing the peer's address to the packet and
   send it to the data relay's address.  The data relay MUST send the
   packet to the peer's address from the relayed address.

   If the data relay receives a UDP packet that is not a HIP control
   packet to the relayed address, it MUST check whether there is a
   permission set for the peer the packet is coming from (i.e., the
   sender's address and SPI value matches to an installed permission),
   and if there is, it MUST forward the packet to the registered host
   that created the permission.  Packets without a permission MUST be
   dropped silently.

   When a host wants to send a UDP encapsulated ESP packet to a peer via
   the data relay, it MUST have an active permission at the data relay
   for the peer with the outbound SPI value it is using.  The host MUST
   send the UDP encapsulated ESP packet to the data relay's address.

   When the data relay receives a UDP encapsulated ESP packet from a
   registered host, it MUST check whether there exists a permission for
   that outbound SPI value.  If such permission exists, the packet MUST
   be forwarded to the address that was registered for the SPI value.
   If no permission exists, the packet is dropped.






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3.5.  Candidate Gathering

   A host needs to gather a set of address candidates before starting
   the connectivity checks.  One server reflexive candidate can be
   discovered during the registration with the HIP relay server from the
   REG_FROM parameter.

   If a host has more than one network interface, additional server
   reflexive candidates can be discovered by sending registration
   requests with Registration Type CANDIDATE_DISCOVERY (value 4) from
   each of the interfaces to a HIP relay server.  When a HIP relay
   server receives a registration request with CANDIDATE_DISCOVERY type,
   it MUST add a REG_FROM parameter, containing the same information as
   if this was a relay registration, to the response.  This request type
   SHOULD NOT create any state at the HIP relay server.

   It is RECOMMENDED that the host also obtains a relayed candidate from
   a HIP data relay as described in Section 3.1.

   Gathering of candidates MAY also be performed like specified in
   Section 4.2 of [I-D.ietf-hip-nat-traversal] if STUN and TURN servers
   are available, or if the host has just a single interface and there
   are no TURN or HIP data relay servers available.

3.6.  Base Exchange via HIP Relay Server

   The Base Exchange is performed as described in Section 4.5 of
   [I-D.ietf-hip-nat-traversal], except that "ICE candidates" are
   replaced by the candidates gathered using procedures described in
   Section 3.5

3.7.  Native NAT Traversal Mode Negotiation

   A host implementing this specification can signal the support for the
   native HIP NAT traversal mode by adding ICE-HIP-UDP NAT traversal
   mode (value 3) in the NAT_TRAVERSAL_MODE [I-D.ietf-hip-nat-traversal]
   parameter.  If this mode is supported by both endpoints, and is the
   most preferred mode out of the all supported modes, further NAT
   traversal procedures are performed as specified in this document.

3.8.  Connectivity Check Pacing Negotiation

   Since the NAT traversal mode specified in this document utilizes
   connectivity checks, the check pacing negotiation MUST be performed
   as specified in Section 4.4 of [I-D.ietf-hip-nat-traversal].  New
   connectivity check transactions MUST NOT be started faster than once
   every Ta (the value negotiated with the TRANSACTION_PACING
   parameter).



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3.9.  Connectivity Checks

   The connectivity checks are performed as described in Section 4.6 of
   [I-D.ietf-hip-nat-traversal] but instead of STUN packets, the
   connectivity checks are HIP UPDATE packets.  See Section 4.3 for
   parameter details.

   As defined in [I-D.ietf-hip-nat-traversal], both hosts MUST form a
   priority ordered checklist and start check transactions every Ta
   milliseconds as long as the checks are running and there are
   candidate pairs whose tests have not started.  The retransmission
   timeout (RTO) for the connectivity check UPDATE packets MUST be
   calculated as defined in Section 4.6 of [I-D.ietf-hip-nat-traversal].

   All connectivity check request packets MUST contain a
   CANDIDATE_PRIORITY parameter with the priority value that would be
   assigned to a peer reflexive candidate if one was learned from this
   check.  The UPDATE packets that acknowledge a connectivity check
   requests MUST be sent from the same address that received the check
   and to the same address where the check was received from.

   The acknowledgment UPDATE packets MUST contain a MAPPED_ADDRESS
   parameter with the port, protocol, and IP address of the address
   where the connectivity check request was received from.

   After a working candidate pair, or pairs, have been discovered, the
   controlling host MUST conclude the checks by nominating the highest
   priority candidate pair for use.  The pair MUST be nominated by
   sending an ESP packet on the selected pair.  If the controlling host
   does not have any data to send, it SHOULD send an ICMP echo request
   using the nominated pair to signal to the controlled host that it can
   stop checks and start using the nominated pair.

   If the connectivity checks failed the hosts SHOULD notify each other
   about the failure with a CONNECTIVITY_CHECKS_FAILED NOTIFY packet.

3.10.  NAT Keepalives

   To keep the NAT bindings towards the HIP relay server and the HIP
   data relay alive, if a registered host has not sent any data or
   control messages to the relay for 15 seconds, it MUST send a HIP
   NOTIFY packet to the relay.  Likewise, if the host has not sent any
   data to a host it has security association and has run connectivity
   checks with, it MUST send either a HIP NOTIFY packet or an ICMP echo
   request using the same locators as the security association is using.






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3.11.  Handling Conflicting SPI Values

   Since the HIP data relay determines from the SPI value to which peer
   an ESP packet should be forwarded, the outbound SPI values need to be
   unique for each relayed address registration.  Thus, if a registered
   host detects that a peer would use an SPI value that is already used
   with another peer via the relay, it MUST NOT select the relayed
   address for use.  The host MAY restart the base exchange to avoid a
   conflict or it MAY refrain from using the relayed candidate for the
   connectivity checks.

   Since the SPI space is 32 bits and the SPI values should be random,
   the probability for a conflicting SPI value is fairly small.
   However, a host with many peers MAY decrease the odds of a conflict
   by registering more than one relayed address using different local
   addresses.


4.  Packet Formats

   The following subsections define the parameter and packet encodings
   for the new HIP parameters used for NAT traversal.  UDP encapsulation
   of the HIP and ESP packets and format of the other required
   parameters is specified in Section 5 of [I-D.ietf-hip-nat-traversal].

4.1.  RELAYED_ADDRESS and MAPPED_ADDRESS Parameters

   The format of the RELAYED_ADDRESS and MAPPED_ADDRESS parameters
   (Figure 1) is identical to REG_FROM, RELAY_FROM and RELAY_TO
   parameters.  This document specifies only use of UDP relaying and
   thus only protocol 17 is allowed.  However, future documents may
   specify support for other protocols.



















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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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Port              |    Protocol   |    Reserved   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Address                            |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type      [TBD by IANA; 952]
     Length    20
     Port      the UDP port number
     Protocol  IANA assigned, Internet Protocol number (17 for UDP)
     Reserved  reserved for future use; zero when sent, ignored
               when received
     Address   an IPv6 address or an IPv4 address in "IPv4-Mapped
               IPv6 address" format

   Figure 1: Format of the RELAYED_ADDRESS and MAPPED_ADDRESS Parameters

4.2.  PEER_PERMISSION Parameter

   The format of the PEER_PERMISSION parameter is shown in Figure 2.
   The parameter is used for setting up and refreshing forwarding rules
   and permissions at the data relay for data packets.  The parameter
   contains one or more sets of Port, Protocol, Address, Outbound SPI,
   and Inbound SPI values.  One set defines a rule for one peer address.




















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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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Port              |    Protocol   |    Reserved   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                             Address                           |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              OSPI                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ISPI                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                              ...                              |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type      [TBD by IANA; 1020]
     Length    length in octets, excluding Type and Length
     Port      the transport layer (UDP) port number
     Protocol  IANA assigned, Internet Protocol number (17 for UDP)
     Reserved  reserved for future use; zero when sent, ignored
               when received
     Address   an IPv6 address, or an IPv4 address in "IPv4-Mapped
               IPv6 address" format, of the peer
     OSPI      the outbound SPI value the registered host is using for
               the peer with the Address and Port
     ISPI      the inbound SPI value the registered host is using for
               the peer with the Address and Port


             Figure 2: Format of the PEER_PERMISSION Parameter

4.3.  HIP Connectivity Check Packets

   The connectivity request messages are HIP UPDATE packets with
   CANDIDATE_PRIORITY parameter (Figure 3).  Response UPDATE packets
   contain a MAPPED_ADDRESS parameter (Figure 1).









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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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Priority                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type      [TBD by IANA; 954]
     Length    4
     Priority  the priority of a peer reflexive candidate

           Figure 3: Format of the CANDIDATE_PRIORITY Parameter


5.  Security Considerations

   If the data relay uses the same relayed address and port for multiple
   registered hosts, it appears to all the peers, and their firewalls,
   that all the registered hosts using the relay are at the same
   address.  Thus, a stateful firewall may allow packets pass from hosts
   that would not normally be able to send packets to a peer behind the
   firewall.  Therefore, a HIP data relay SHOULD NOT re-use the port
   numbers.  If port numbers need to be re-used, the relay SHOULD have a
   sufficiently large pool of port numbers and select ports from the
   pool randomly to decrease the chances of a registered host obtaining
   the same address that a certain other host is using.


6.  Acknowledgements

   This document re-uses many of the ideas proposed in various earlier
   HIP NAT traversal related drafts by Miika Komu, Simon Schuetz, Martin
   Stiemerling, Pekka Nikander, Marcelo Bagnulo, Vivien Schmitt, Abhinav
   Pathak, Lars Eggert, Thomas Henderson, Hannes Tschofenig, and Philip
   Matthews.


7.  IANA Considerations

   This section is to be interpreted according to [RFC5226].

   This document updates the IANA Registry for HIP Parameter Types
   [RFC5201] by assigning new HIP Parameter Type value for the new HIP
   Parameter: RELAYED_ADDRESS (defined in Section 4.1).

   This document also updates the IANA Registry for HIP NAT traversal
   modes [I-D.ietf-hip-nat-traversal] by assigning value for the NAT



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   traversal mode ICE-HIP-UDP (defined in Section 3.7).

   This document defines additional registration types for the HIP
   Registration Extension [RFC5203] that allow registering with a HIP
   relay server for ESP relaying service: RELAY_UDP_ESP (defined in
   Section 3.1); and performing server reflexive candidate discovery:
   CANDIDATE_DISCOVERY (defined in Section 3.5).

   The IANA Registry for HIP Registration Failure Types is updated with
   new Failure Types "Insufficient resources" (defined in Section 3.1)
   and "Invalid certificate" (defined in Section 3.2).


8.  References

8.1.  Normative References

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

   [RFC5201]  Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
              "Host Identity Protocol", RFC 5201, April 2008.

   [RFC5202]  Jokela, P., Moskowitz, R., and P. Nikander, "Using the
              Encapsulating Security Payload (ESP) Transport Format with
              the Host Identity Protocol (HIP)", RFC 5202, April 2008.

   [RFC5203]  Laganier, J., Koponen, T., and L. Eggert, "Host Identity
              Protocol (HIP) Registration Extension", RFC 5203,
              April 2008.

   [RFC5207]  Stiemerling, M., Quittek, J., and L. Eggert, "NAT and
              Firewall Traversal Issues of Host Identity Protocol (HIP)
              Communication", RFC 5207, April 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [I-D.ietf-hip-nat-traversal]
              Komu, M., Henderson, T., Tschofenig, H., Melen, J., and A.
              Keranen, "Basic HIP Extensions for Traversal of Network
              Address Translators", draft-ietf-hip-nat-traversal-09
              (work in progress), October 2009.



Keranen & Melen         Expires October 11, 2010               [Page 13]


Internet-Draft        HIP Native NAT Traversal Mode           April 2010


   [I-D.ietf-mmusic-ice]
              Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols",
              draft-ietf-mmusic-ice-19 (work in progress), October 2007.

   [I-D.ietf-hip-cert]
              Heer, T. and S. Varjonen, "HIP Certificates",
              draft-ietf-hip-cert-02 (work in progress), October 2009.

8.2.  Informative References

   [I-D.ietf-behave-turn]
              Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)",
              draft-ietf-behave-turn-16 (work in progress), July 2009.


Authors' Addresses

   Ari Keranen
   Ericsson
   Hirsalantie 11
   02420 Jorvas
   Finland

   Email: Ari.Keranen@ericsson.com


   Jan Melen
   Ericsson
   Hirsalantie 11
   02420 Jorvas
   Finland

   Email: Jan.Melen@ericsson.com














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