Network Working Group                                         E. Ertekin
Internet-Draft                                               C. Christou
Expires: August 6, 2009 February 13, 2010                                     R. Jasani
                                                     Booz Allen Hamilton
                                                              T. Kivinen
                                                           Safenet, Inc.
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                        February 2,
                                                         August 12, 2009

    IKEv2 Extensions to Support Robust Header Compression over IPsec

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   In order to integrate ROHC with IPsec [ROHCOIPSEC], a mechanism is
   needed to signal ROHC channel parameters between end-points.
   Internet Key Exchange (IKE) is a mechanism which can be leveraged to
   exchange these parameters.  This document specifies extensions to
   IKEv2 [IKEV2] that will allow ROHC and its associated channel
   parameters to be signaled for IPsec security associations (SAs).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3  4
   2.  ROHC Channel Initialization for ROHCoIPsec . . . . . . . . . . 3  4
     2.1.  ROHC Channel Parameters that are Signaled  . . . . . . . . . 3  4
       2.1.1.  ROHC_SUPPORTED Notify Message  . . . . . . . . . . . . . 4  5
       2.1.2.  ROHC Attribute Types . . . . . . . . . . . . . . . . . 5  6
     2.2.  ROHC Channel Parameters that are Implicitly Set  . . . . . . 7  9
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . . . 7  9
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . . 7  9
   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . 8 10
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 9 10
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 9 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 11

1.  Introduction

   Increased packet header overhead due to IPsec [IPSEC] can result in
   the inefficient utilization of bandwidth.  Coupling ROHC [ROHC] with
   IPsec offers an efficient way to transfer protected IP traffic.

   ROHCoIPsec [ROHCOIPSEC] requires configuration parameters to be
   initialized at the compressor and decompressor.  Current
   specifications for hop-by-hop ROHC negotiate these parameters through
   a link-layer protocol such as Point-to-Point Protocol (PPP) (i.e.
   ROHC over PPP [ROHC-PPP]).  Since key exchange protocols (e.g.
   IKEv2) can be used to dynamically establish parameters between IPsec
   peers, this document defines extensions to IKEv2 to signal ROHC
   parameters for ROHCoIPsec.

2.  ROHC Channel Initialization for ROHCoIPsec

   The following subsections define extensions to IKEv2 which enables an
   initiator and a responder to signal parameters required to establish
   a ROHC channel for a ROHCoIPsec session.

2.1.  ROHC Channel Parameters that are Signaled

   ROHC channel parameters will be signaled at either the establishment
   or rekeying of a Child SA.  Specifically, a new Notify message type
   is used during the IKE_AUTH and CREATE_CHILD_SA exchanges to convey
   these parameters.

   The Notify payload sent by the initiator contains the channel
   parameters for the ROHC implementation.  Specifically, these
   parameters indicate the capabilities of the ROHC decompressor at the
   initiator.  Upon receipt of the initiator's request, the responder
   will either ignore the payload (if it doesn't support ROHC or the
   proposed parameters) or respond with a Notify payload that contains
   its own ROHC channel parameters.

   Note that only one Notify payload is used to convey ROHC parameters.
   If multiple Notify payloads containing ROHC parameters are received,
   all but the first such Notify payload must be dropped.  If the
   initiator does not receive a Notify Payload with the responder's ROHC
   channel parameters, ROHC must not be enabled on the Child SA.

   A new Notify Message Type value, denoted ROHC_SUPPORTED, indicates
   that the Notify payload is conveying ROHC channel parameters.  The
   value for the ROHC_SUPPORTED message is specified in Section 4.

   The Notify Payload (defined in [IKEV2]) is illustrated in Figure 1.

                           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
      ! Next Payload  !C!  RESERVED   !         Payload Length        !
      !  Protocol ID  !   SPI Size    !      Notify Message Type      !
      !                                                               !
      ~                Security Parameter Index (SPI)                 ~
      !                                                               !
      !                                                               !
      ~                       Notification Data                       ~
      !                                                               !

                         Figure 1. Notify Payload format.

   The fields of the Notify Payload are set as follows:

   Next Payload (1 octet)
      Identifier for the payload type of the next payload in the
      message.  Further details can be found in [IKEV2].

   Critical (1 bit)
      Since all IKEv2 implementations must support the Notify Payload,
      this value is zero.

   Payload Length (2 octets)
      As defined in [IKEV2], this field indicates the length of the
      current payload, including the generic payload header.

   Protocol ID (1 octet)
      Since this Notification message is used during the creation of a
      Child SA, this field must be set to zero.

   SPI Size (1 octet)
      This value must be set to zero, since no SPI is applicable (ROHC
      parameters are set at SA creation, thus the SPI has not been

   Notify Message Type (2 octets)
      This field must be set to ROHC_SUPPORTED.

2.1.1.  ROHC_SUPPORTED Notify Message

   The ROHC_SUPPORTED Notify message is used to signal channel
   parameters between ROHCoIPsec compressor and decompressor.  The
   message contains a list of "ROHC Attributes" which contain the
   parameters required for the ROHCoIPsec session.

   The format for signaling ROHC Attributes takes a similar format to
   the Transform Attributes described in Section 3.3.5 of [IKEV2].  The
   ROHC Attribute is shown in Figure 2.

                            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
       !A!     ROHC Attribute Type     !  AF=0  ROHC Attribute Length  !
       !F!                             !  AF=1  ROHC Attribute Value   !
       !                   AF=0  ROHC Attribute Value                  !
       !                   AF=1  Not Transmitted                       !

                 Figure 2.  Format of the ROHC Attribute.

   o  ROHC Attribute Type (2 octets) - Unique identifier for each type
      of ROHC attribute (see Section 2.1.2).  The most significant bit
      in the field is the Attribute Format (AF) bit.  If the AF bit is a
      zero (0), then the ROHC Attribute is expressed in a Type/Length/
      Value (TLV) format.  If the AF bit is a one (1), then the ROHC
      Attribute is expressed in a Type/Value (TV) format.
   o  ROHC Attribute Length (2 octets) - Length (in octets) of the
      Attribute Value.  When the AF bit is a one (1), the ROHC Attribute
      Value is 2 octets and the ROHC Attribute Length field is not
   o  ROHC Attribute Value (variable length) - Value of the ROHC
      Attribute associated with the ROHC Attribute Type.  If the AF bit
      is a zero (0), this field's length is defined by the ROHC
      Attribute Length field.  If the AF bit is a one (1), the length of
      the ROHC Attribute Value is 2 octets.

2.1.2.  ROHC Attribute Types

   This section describes four five ROHC Attribute Types: MAX_CID,
   ROHC_PROFILE, ROHC_INTEG, ROHC_ICV_LEN, and ROHC_ICV_LEN. MRRU.  The value which defines
   allocated for each ROHC Attribute Type is specified in Section 4.

   Maximum Context Identifier (MAX_CID, AF = 1)
      The MAX_CID attribute is a mandatory attribute.  Exactly one
      MAX_CID attribute must be sent.  The MAX_CID field indicates the
      maximum value of a context Identifier supported by the ROHCoIPsec
      decompressor.  This attribute value is two octets in length.  The
      range of values for MAX_CID must be at least 0 and at most 16383
      (the value 0 implies having one context).  The recipient of the
      MAX_CID Attribute must only use up to MAX_CID context identifiers
      for compression.

      Suggested value: 15

   ROHC Profile (ROHC_PROFILE, AF = 1)
      The ROHC_PROFILE attribute is a mandatory attribute.  At least one
      ROHC_PROFILE attribute(s) must be sent.  A  Each
      ROHC_PROFILE attribute
      contains has a fixed length of 4 octets, and its
      attribute value is a two-octet long profile supported by identifier.  There may
      be one or more ROHC_PROFILE attribute(s) included in the ROHCoIPsec
      ROHC_SUPPORTED Notify Message.  If multiple ROHC_PROFILE
      attributes are sent, the order is arbitrary.  The recipient of a
      ROHC_PROFILE attribute(s) must only use the profile(s) proposed
      for compression.

      Several common profiles are defined in [ROHCV1] and [ROHCV2].
      Note, however, that two versions of the same profile must not be
      signaled.  For example, if a ROHCoIPsec decompressor supports both
      ROHCv1 UDP (0x0002) and ROHCv2 UDP profiles, (0x0102), both profiles must
      not be signaled.  This restriction is needed, as packets
      compressed by ROHC express only the 8 least significant bits of
      the profile identifier; since the 8 least significant bits for
      corresponding profiles in ROHCv1 and ROHCv2 are identical, the
      decompressor is not capable of determining the ROHC version that
      was used to compress the packet.

   Integrity Algorithm for Verification of Decompressed Headers
   (ROHC_INTEG, AF = 1)
      The ROHC_INTEG attribute is a mandatory attribute.  There must be
      at least one ROHC_INTEG attribute contained within the
      ROHC_SUPPORTED Notify message.  The attribute contains an
      integrity algorithm that is used to ensure the integrity of the
      decompressed packets (i.e. ensure that the packet headers are
      properly decompressed).

      Authentication algorithms that must be supported are specified in
      Section 3.2 of [CRYPTO-ALG].  More explicitly, the implementation
      conformance requirements for authentication algorithms are as

      Requirement    Algorithm
      -----------    ----------------
      Must           AUTH_HMAC_SHA1_96
      Should+        AUTH_AES_XCBC_MAC_96
      May            AUTH_HMAC_MD5_96
      The integrity algorithm is represented by a two octet value that
      corresponds to the value listed in [IKEV2-
      PARA] [IKEV2-PARA] "For Transform
      Type 3 (Integrity Algorithm)" section.  Upon receipt of the
      ROHC_INTEG attribute(s), the responder must select exactly one of
      proposed algorithms and send the selected algorithm back to the
      initiator.  The selected integrity algorithm must be used in both

      It is noted that:
      1.  The key for this Integrity Algorithm is computed using the
          same method as is used to compute IPsec's Integrity Algorithm
          key ([IKEV2], Section 2.17).  When a ROHC-enabled CHILD_SA is
          rekeyed, the key associated with this integrity algorithm is
          rekeyed as well.
      2.  A ROHCoIPsec initiator may signal a value of zero (0x0000) in
          a ROHC_INTEG attribute.  This corresponds to "NONE" in the
          Integrity Algorithm Transform ID registry.  The ROHCoIPsec
          responder may select this value by responding to the initiator
          with a ROHC_INTEG attribute of zero (0x0000).  In this
          scenario, no integrity algorithm is applied in either

   Integrity Algorithm Length (ROHC_ICV_LEN, AF = 1)
      The ROHC_ICV_LEN attribute is an optional attribute.  There may be
      zero or one ROHC_ICV_LEN attribute contained within the
      ROHC_SUPPORTED Notify message.  The attribute specifies the number
      of ICV octets the sender expects to receive on incoming ROHC
      packets.  The ICV of the negotiated ROHC_INTEG algorithms are
      truncated to ROHC_ICV_LEN bytes by taking the first ROHC_ICV_LEN
      bytes of the output.  Both the initiator and responder announce
      their preference for their own ICV length.  The recipient of the
      ROHC_ICV_LEN attribute must truncate the ICV to the length
      contained in the message.  If ROHC_ICV_LEN length is zero, then no
      ICV is calculated or sent.  If no ROHC_ICV_LEN attribute is sent
      at all or the ROHC_ICV_LEN is larger than the length of the ICV of
      selected algorithm, then the full ICV length as specified by the
      ROHC_INTEG algorithm is sent.

   Maximum reconstructed reception unit (MRRU, AF = 1)
      The MRRU attribute is an optional attribute.  There may be zero or
      one MRRU attribute contained within the ROHC_SUPPORTED Notify
      message.  If present, the attribute value is two octets in length.
      The attribute specifies the size of the largest reconstructed unit
      in octets that the ROHCoIPsec decompressor is expected to
      reassemble from ROHC segments.  This size includes the CRC, and
      the ROHC ICV.  If MRRU is 0 or if no MRRU attribute is sent, no
      segment headers are allowed on the ROHCoIPsec channel.

   If an unknown ROHC Attribute Type Value is received, it is silently

2.2.  ROHC Channel Parameters that are Implicitly Set

   The following ROHC channel parameters are not signaled:
   o  LARGE_CIDS: This value is implicitly determined by the value of
      MAX_CID (e.g. if MAX_CID is <= 15, LARGE_CIDS is assumed to be 0).
   o  MRRU: IPsec implementations will always implement path MTU
      discovery; therefore, ROHC packets will never need to use ROHC
      segmentation over an IPsec SA.  As a result, this value will
      always be zero, and does not need to be signaled.
   o  FEEDBACK_FOR: When a pair of SAs are created (one in each
      direction), the ROHC channel parameter FEEDBACK_FOR is set
      implicitly to the other SA of the pair (i.e. the SA pointing in
      the reverse direction).

3.  Security Considerations

   The ROHC channel parameters signaled via IKEv2 do not add any new
   vulnerabilities beyond those associated with the normal operation of

4.  IANA Considerations

   This document defines a new Notify Message (Status Type).  Therefore,
   IANA is requested to allocate one value from the IKEv2 Notify Message
   registry to indicate ROHC_SUPPORTED.  Note that, since this Notify
   Message is a Status Type, values ranging from 0 to 16383 must not be
   allocated for ROHC_SUPPORTED.

   In addition, IANA is requested to allocate a "ROHC Attribute Types"
   registry in the IKEv2 Parameters Registry [IKEV2-PARA].  Within the
   "ROHC Attribute Types" registry, this document allocates the
   following values:

   Value     ROHC Attribute Type                            Reference
   0         RESERVED                                       [rfcThis]
   1         Maximum value of context identifier Context Identifier (MAX_CID)           [rfcThis]
   2         ROHC Profile (ROHC_PROFILE)                    [rfcThis]
   3         ROHC Integrity Algorithm (ROHC_INTEG)          [rfcThis]
   4         ROHC ICV Length in bytes (ROHC_ICV_LEN)        [rfcThis]
   5         Maximum Reconstructed Reception Unit (MRRU)    [rfcThis]
   6-65536   Unassigned

   Following the policies outlined in [IANA-CONSIDERATIONS], the IANA
   policy for assigning new values for the ROHC Attribute Types registry
   shall be Specification Required: values and their meanings must be
   documented in a permanent and readily available public specification,
   in sufficient detail so that interoperability between independent
   implementations is possible.

5.  Acknowledgments

   The authors would like to thank Mr. Sean O'Keeffe, Mr. James Kohler,
   and Ms. Linda Noone of the Department of Defense, as well as Mr. Rich
   Espy of OPnet for their contributions and support in the development
   of this document.

   The authors would also like to thank Mr. Yoav Nir, and Mr. Robert A
   Stangarone Jr.: both served as committed document reviewers for this

   In addition, the authors would like to thank the following for their
   numerous reviews and comments to this document:

   o  Mr. Magnus Westerlund
   o  Dr. Stephen Kent
   o  Mr. Lars-Erik Jonsson
   o  Mr. Pasi Eronen
   o  Dr. Jonah Pezeshki
   o  Mr. Carl Knutsson
   o  Dr. Joseph Touch

   Finally, the authors would also like to thank Mr. Tom Conkle, Ms.
   Michele Casey, and Mr. Etzel Brower.

6.  References

6.1.  Normative References

   [IPSEC]    Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [ROHC]     Jonsson, L-E., Pelletier, G., and K. Sandlund, "The RObust
              Header Compression (ROHC) Framework", RFC 4995, July 2007.

   [IKEV2]    Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [ROHCV1]   Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
              Hannu, H., Jonsson, L., Hakenberg, R., Koren, T., Le, K.,
              Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
              Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
              Compression (ROHC): Framework and four profiles: RTP, UDP,
              ESP, and uncompressed", RFC 3095, July 2001.

   [ROHCV2]   Pelletier, G. and K. Sandlund, "RObust Header Compression
              Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and UDP
              Lite", RFC 5225, April 2008.

6.2.  Informative References

              Ertekin, E., Jasani, R., Christou, C., and C. Bormann,
              "Integration of Header Compression over IPsec Security
              Associations", work in progress , February August 2009.

              Bormann, C., "Robust Header Compression (ROHC) over PPP",
              RFC 3241, April 2002.

              Manral, V., "Cryptographic Algorithm Implementation
              Requirements for Encapsulating Security Payload (ESP) and
              Authentication Header (AH)", RFC 4835, April 2007.

              IANA, "IKEv2 Parameters,
              January 2008.

              Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              October 1998.

Authors' Addresses

   Emre Ertekin
   Booz Allen Hamilton
   13200 Woodland Park Dr.
   Herndon, VA  20171

   Chris Christou
   Booz Allen Hamilton
   13200 Woodland Park Dr.
   Herndon, VA  20171


   Rohan Jasani
   Booz Allen Hamilton
   13200 Woodland Park Dr.
   Herndon, VA  20171


   Tero Kivinen
   Safenet, Inc.
   Fredrikinkatu 47


   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28334