HIP Working Group                                             A. Keranen
Internet-Draft                                                  Ericsson
Intended status: Experimental                           October 18, 2010
Expires: April 21, 2011

        Host Identity Protocol Signaling Message Transport Modes


   This document specifies two transport modes for Host Identity
   Protocol (HIP) signaling messages that allow conveying them over
   encrypted connections initiated with the Host Identity Protocol.

Status of this Memo

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

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   document authors.  All rights reserved.

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   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 Extensions . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Mode Negotiation in HIP Base Exchange . . . . . . . . . . . 3
     3.2.  Mode Negotiation After HIP Base Exchange  . . . . . . . . . 5
     3.3.  HIP Messages on Encrypted Connections . . . . . . . . . . . 5
       3.3.1.  ESP mode  . . . . . . . . . . . . . . . . . . . . . . . 6
       3.3.2.  ESP-TCP mode  . . . . . . . . . . . . . . . . . . . . . 6
     3.4.  Recovering from Failed Encrypted Connections  . . . . . . . 6
     3.5.  Host Mobility . . . . . . . . . . . . . . . . . . . . . . . 7
   4.  Notify Packet Types . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informational References  . . . . . . . . . . . . . . . . . 9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   Host Identity Protocol (HIP) [RFC5201] signaling messages can be
   exchanged over plain IP using the protocol number reserved for this
   purpose, or over UDP using the UDP port reserved for HIP NAT
   traversal [RFC5770].  When two hosts perform a HIP base exchange,
   they set up an encrypted connection between them for data traffic,
   but continue to use plain IP or UDP for HIP signaling messages.

   This document defines how the encrypted connection can be used also
   for HIP signaling messages.  Two different modes are defined: HIP
   over Encapsulating Security Payload (ESP) and HIP over TCP.  The
   benefit of sending HIP messages over ESP is that all signaling
   traffic (including HIP headers) will be encrypted.  If HIP messages
   are sent over TCP (which in turn is transported over ESP), TCP can
   handle also message fragmentation where needed.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Protocol Extensions

   This section defines how support for different HIP signaling message
   transport modes is negotiated and the normative behavior required by
   the extension.

3.1.  Mode Negotiation in HIP Base Exchange

   A HIP host implementing this specification SHOULD indicate the modes
   it supports, and is willing to use, in the base exchange.  The HIP
   signaling message transport mode negotiation is similar to HIP NAT
   traversal mode negotiation: first the Responder lists the supported
   modes in a HIP_TRANSPORT_MODE parameter (see Figure 1) in the R1
   packet.  The modes are listed in priority order; the more preferred
   mode(s) first.  If the Initiator supports, and is willing to use, any
   of the modes proposed by the Responder, it selects one of the modes
   by adding a HIP_TRANSPORT_MODE parameter containing the selected mode
   to the I2 packet.  Finally, if the Initiator selected one of the
   modes and the base exchange succeeds, hosts MUST use the selected
   mode for the following HIP signaling messages sent between them for
   the duration of the HIP association or until another mode is

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   If the Initiator cannot or will not use any of the modes proposed by
   the Responder, the Initiator SHOULD include an empty
   HIP_TRANSPORT_MODE parameter to the I2 packet to signal that it
   support this extension but will not use any of the proposed modes.
   Depending on local policy, the Responder MAY either abort the base
   exchange or continue HIP signaling without using an encrypted
   connection, if there was no HIP_TRANSPORT_MODE parameter in I2 or the
   parameter was empty.  If the Initiator selects a mode that the
   Responder does not support (and hence was not included in R1), the
   Responder MUST abort the base exchange.  If the base exchange is
   aborted due to (possibly lack of) HIP_TRANSPORT_PARAMETER, the
   (see Section 4) to the Initiator.

      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            |
     |           Mode ID #1          |            Mode ID #2         |
     |           Mode ID #n          |             Padding           |

     Type     [ TBD by IANA; 7680 ]
     Length   length in octets, excluding Type, Length, and Padding
     Mode ID  defines the proposed or selected transport mode(s)

     The following Mode IDs are defined:

         ID name   Value
         RESERVED    0
         DEFAULT     1
         ESP         2
         ESP-TCP     3

           Figure 1: Format of the HIP_TRANSPORT_MODE parameter

   The mode DEFAULT indicates that the same transport mode (e.g., plain
   IP or UDP) that was used for the base exchange should be used for
   subsequent HIP signaling messages.  In the ESP mode the messages are
   sent as such on the encrypted ESP connection and in the ESP-TCP mode
   TCP is used within the ESP tunnel.

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3.2.  Mode Negotiation After HIP Base Exchange

   If a HIP hosts wants to change to a different transport mode (or
   start using a transport mode) some time after the base exchange, it
   sends a HIP UPDATE packet with a HIP_TRANSPORT_MODE parameter
   containing the mode(s) it would prefer to use.  The host receiving
   the UPDATE SHOULD respond with an UPDATE packet containing the mode
   that is selected as in the negotiation during the base exchange.  If
   the receiving host does not support, or is not willing to use, any of
   the listed modes, it SHOULD respond with an UPDATE packet where the
   HIP_TRANSPORT_MODE parameter contains only the currently used
   transport mode (even if one was not included in the previous UPDATE
   packet) and continue using that mode.

   Since the HIP_TRANSPORT_MODE parameter's type is not critical (as
   defined in Section 5.2.1 of [RFC5201]), a host not supporting this
   extension would simply reply with an acknowledgement UPDATE packet
   without a HIP_TRANSPORT_MODE parameter.  In such a case, depending on
   local policy as in mode negotiation during the base exchange, the
   host that requested the new transport mode MAY close the HIP
   association.  If the association is closed, the host closing the
   association SHOULD send a NO_VALID_HIP_TRANSPORT_MODE NOTIFY packet
   to the other host before closing the association.

3.3.  HIP Messages on Encrypted Connections

   This specification defines two different transport modes for sending
   HIP packets over encrypted ESP connections.  These modes require that
   the ESP transport format [RFC5202] is negotiated to be used between
   the hosts.  If the ESP transport format is not used, these modes MUST
   NOT be offered in the HIP_TRANSPORT_MODE parameter.  If a
   HIP_TRANSPORT_MODE parameter containing an ESP transport mode is
   received but the ESP transport format is not used, a host MUST NOT
   select such a mode but act as specified in Section 3.1 (if performing
   a base exchange) or Section 3.2 (if performing an UPDATE) when no
   valid mode is offered.

   The ESP mode provides simple protection for all the signaling traffic
   and can be used as a generic replacement for the DEFAULT mode in
   cases where all signaling traffic should be encrypted.  If the HIP
   messages may become so large that they would need to be fragmented,
   e.g., because of HIP certificates [I-D.ietf-hip-cert] or DATA
   messages [I-D.ietf-hip-hiccups], it is RECOMMENDED to use the ESP-TCP
   mode which can handle message fragmentation at TCP level instead of
   relying on IP level fragmentation.

   HIP messages that result in changing or generating new keying
   material, i.e., the base exchange and re-keying UPDATE messages, MUST

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   NOT be sent over an encrypted connection that is created using the
   keying material that is being changed, nor over an encrypted
   connection using the newly created keying material.

3.3.1.  ESP mode

   If the ESP mode is selected in the base exchange, both hosts MUST
   listen for incoming HIP signaling messages and send outgoing messages
   on the encrypted connection.  The ESP header's next header value for
   such messages MUST be set to HIP (139).

3.3.2.  ESP-TCP mode

   If the ESP-TCP mode is selected, the host with the larger HIT
   (calculated as defined in Section 6.5 of [RFC5201]) MUST start to
   listen for an incoming TCP connection on the port 10500 on the
   encrypted connection and the other host MUST create a TCP connection
   to that port.  The host with the smaller HIT SHOULD use port 10500 as
   the source port for the TCP connection.  Once the TCP connection is
   established, both hosts MUST listen for incoming HIP signaling
   messages and send the outgoing messages using the TCP connection.
   The ESP next header value for messages sent using the ESP-TCP mode
   connections MUST be set to TCP (6).

   If the hosts are unable to create the TCP connection, the host that
   initiated the mode negotiation MUST restart the negotiation with
   UPDATE message and SHOULD NOT propose the ESP-TCP mode.  If local
   policy does not allow using any other mode than ESP-TCP, the HIP
   association MUST be closed.  The UPDATE or CLOSE message MUST be sent
   using the same transport mode that was used for negotiating the use
   of the ESP-TCP mode.

   Since TCP provides reliable transport, the HIP messages sent over TCP
   MUST NOT be retransmitted for the purpose of achieving reliable
   transmission.  Instead, a host SHOULD wait to detect that the TCP
   connection has failed to retransmit the packet successfully in a
   timely manner (such detection is platform- and policy-specific)
   before concluding that there is no response.

3.4.  Recovering from Failed Encrypted Connections

   If the encrypted connection fails for some reason, it can no longer
   be used for HIP signaling and the hosts SHOULD re-establish the
   connection using HIP messages that are sent outside of the encrypted
   connection.  Hence, while listening for incoming HIP messages on the
   encrypted connection, hosts MUST still accept incoming HIP messages
   using the same transport method (e.g., UDP or plain IP) that was used
   for the base exchange.  When responding to a HIP message sent outside

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   of encrypted connection, the response MUST be sent using the same
   transport method as the original message used.  Hosts SHOULD send
   outside of the encrypted connection only HIP messages that are used
   to reestablish the encrypted connection.  Especially, messages that
   are intended to be sent only encrypted (e.g., DATA messages using an
   encrypted transport mode) MUST NOT be sent before the encrypted
   connection is reestablished.

   The UPDATE messages used for re-establishing the encrypted connection
   MUST contain a HIP_TRANSPORT_MODE parameter and the negotiation
   proceeds as described in Section 3.2.

3.5.  Host Mobility

   If the host's address changes, it may not be able to send the
   mobility UPDATE messages using the encrypted connection before it
   breaks.  This results in a similar situation as if the encrypted
   connection had failed and the hosts need to re-negotiate the new
   addresses using un-encrypted UPDATE messages and possibly rendezvous
   [RFC5204] or HIP relay [RFC5770] servers.  Also these UPDATE messages
   MUST contain the HIP_TRANSPORT_MODE parameter and perform the
   transport mode negotiation.

4.  Notify Packet Types

   The new Notify Packet Type [RFC5201] defined in this document is
   shown below.  The Notification Data field for the error notifications
   SHOULD contain the HIP header of the rejected packet.

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


      If a host sends an UPDATE message that does not have any transport
      mode the receiving host is willing to use, the receiving host
      sends back a NOTIFY error packet with this type.

5.  Security Considerations

   By exchanging the HIP messages over ESP connection, all HIP signaling
   data (after the base exchange but excluding keying material
   (re)negotiation) will be encrypted, but only if NULL encryption is
   not used.  Thus, a host requiring confidentiality for the HIP
   signaling messages must check that encryption is negotiated to be
   used on the ESP connection.  Moreover, the level of protection

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   provided by the ESP transport modes depends on the selected ESP
   transform; see [RFC5202] and [RFC4303] for security considerations of
   the different ESP transforms.

6.  Acknowledgements

   Thanks to Gonzalo Camarillo, Kristian Slavov, Tom Henderson, Miika
   Komu, and Jan Melen for comments on the draft.

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
   HIP_TRANSPORT_MODE parameter (defined in Section 3.1).

   The HIP_TRANSPORT_MODE parameter has 16-bit unsigned integer fields
   for different modes, for which IANA is to create and maintain a new
   sub-registry entitled "HIP Transport Modes" under the "Host Identity
   Protocol (HIP) Parameters" registry.  Initial values for the
   transport mode registry are given in Section 3.1; future assignments
   are to be made through IETF Review [RFC5226].  Assignments consist of
   a transport mode identifier name and its associated value.

   This document also defines new HIP Notify Packet Type [RFC5201]

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.

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

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8.2.  Informational References

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC5204]  Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
              Rendezvous Extension", RFC 5204, April 2008.

   [RFC5770]  Komu, M., Henderson, T., Tschofenig, H., Melen, J., and A.
              Keranen, "Basic Host Identity Protocol (HIP) Extensions
              for Traversal of Network Address Translators", RFC 5770,
              April 2010.

              Heer, T. and S. Varjonen, "HIP Certificates",
              draft-ietf-hip-cert-04 (work in progress), September 2010.

              Camarillo, G. and J. Melen, "HIP (Host Identity Protocol)
              Immediate Carriage and Conveyance of Upper- layer Protocol
              Signaling (HICCUPS)", draft-ietf-hip-hiccups-05 (work in
              progress), July 2010.

Author's Address

   Ari Keranen
   Hirsalantie 11
   02420 Jorvas

   Email: Ari.Keranen@ericsson.com

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