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RFC 5857

Proposed STD
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IKEv2 Extensions to Support Robust Header Compression over IPsec


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Internet Engineering Task Force (IETF)                        E. Ertekin
Request for Comments: 5857                                   C. Christou
Category: Standards Track                                      R. Jasani
ISSN: 2070-1721                                      Booz Allen Hamilton
                                                              T. Kivinen
                                                         AuthenTec, Inc.
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                                May 2010

    IKEv2 Extensions to Support Robust Header Compression over IPsec


   In order to integrate Robust Header Compression (ROHC) with IPsec, a
   mechanism is needed to signal ROHC channel parameters between
   endpoints.  Internet Key Exchange (IKE) is a mechanism that can be
   leveraged to exchange these parameters.  This document specifies
   extensions to IKEv2 that will allow ROHC and its associated channel
   parameters to be signaled for IPsec Security Associations (SAs).

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Page 2 
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
   ( 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 Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. ROHC Channel Initialization for ROHCoIPsec ......................3
      3.1. ROHC_SUPPORTED Notify Message ..............................3
           3.1.1. ROHC Attributes .....................................5
           3.1.2. ROHC Attribute Types ................................6
      3.2. ROHC Channel Parameters That Are Implicitly Set ............9
   4. Security Considerations .........................................9
   5. IANA Considerations .............................................9
   6. Acknowledgments ................................................10
   7. References .....................................................11
      7.1. Normative References ......................................11
      7.2. Informative References ....................................12

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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 the Point-to-Point Protocol (PPP)
   (i.e., ROHC over PPP [ROHC-PPP]).  Since key exchange protocols
   (e.g., IKEv2 [IKEV2]) can be used to dynamically establish parameters
   between IPsec peers, this document defines extensions to IKEv2 to
   signal ROHC parameters for ROHCoIPsec.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [BRA97].

3.  ROHC Channel Initialization for ROHCoIPsec

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

3.1.  ROHC_SUPPORTED Notify Message

   ROHC channel parameters MUST be signaled separately for each ROHC-
   enabled IPsec SA.  Specifically, a new Notify message type MUST be
   included in the IKE_AUTH and CREATE_CHILD_SA exchanges whenever a new
   ROHC-enabled IPsec SA is created, or an existing one is rekeyed.

   The Notify payload sent by the initiator MUST contain the channel
   parameters for the ROHC session.  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

   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.

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   A new Notify Message Type value, denoted ROHC_SUPPORTED, indicates
   that the Notify payload is conveying ROHC channel parameters (Section

   The Notify payload (defined in RFC 4306 [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 RFC 4306 [IKEV2].

   Critical (1 bit)

      Since all IKEv2 implementations support the Notify payload, this
      value MUST be set to zero.

   Payload Length (2 octets)

      As defined in RFC 4306 [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.

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   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.

   Security Parameter Index (SPI)

      Since the SPI Size field is 0, this field MUST NOT be transmitted.

   Notification Data (variable)

      This field MUST contain at least three ROHC Attributes (Section

3.1.1.  ROHC Attributes

   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 RFC 4306
   [IKEV2].  The format of 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  Attribute Format (AF) (1 bit) - If the AF bit is a zero (0), then
      the ROHC Attribute is expressed in a Type/Length/Value format.  If
      the AF bit is a one (1), then the ROHC attribute is expressed in a
      Type/Value (TV) format.

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   o  ROHC Attribute Type (15 bits) - Unique identifier for each type of
      ROHC attribute (Section 3.1.2).

   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.

3.1.2.  ROHC Attribute Types

   This section describes five ROHC Attribute Types: MAX_CID,
   allocated for each ROHC Attribute Type is specified in Section 4.

   MAX_CID (Maximum Context Identifier, 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 2 octets in length.  The
      value for MAX_CID MUST be at least 0 and at most 16383.  Since
      CIDs can take values between 0 and MAX_CID, the actual number of
      contexts that can be used are MAX_CID+1.  If MAX_CID is 0, this
      implies having one context.  The recipient of the MAX_CID
      Attribute MUST only use context identifiers up to MAX_CID for

      Note that the MAX_CID parameter is a one-way notification (i.e.,
      the sender of the attribute indicates what it can handle to the
      other end); therefore, different values for MAX_CID may be
      announced in each direction.

   ROHC_PROFILE (ROHC Profile, AF = 1)

      The ROHC_PROFILE attribute is a mandatory attribute.  Each
      ROHC_PROFILE attribute has a fixed length of 4 octets, and its
      attribute value is a 2-octet long ROHC Profile Identifier
      [ROHCPROF].  There MUST be at least one ROHC_PROFILE attribute
      included in the 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.

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      Several common profiles are defined in RFCs 3095 [ROHCV1] and 5225
      [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 (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.

      Note that the ROHC_PROFILE attribute is a one-way notification;
      therefore, different values for ROHC_PROFILE may be announced in
      each direction.

   ROHC_INTEG (Integrity Algorithm for Verification of Decompressed
   Headers, 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 value contains the
      identifier of an integrity algorithm that is used to ensure the
      integrity of the decompressed packets (i.e., ensure that the
      decompressed packet headers are identical to the original packet
      headers prior to compression).

      Authentication algorithms that MUST be supported are specified in
      the "Authentication Algorithms" table in Section 3.1.1 ("ESP
      Encryption and Authentication Algorithms") of RFC 4835
      [CRYPTO-ALG] (or its successor).

      The integrity algorithm is represented by a 2-octet value that
      corresponds to the value listed in the IKEv2 Parameters registry
      [IKEV2-PARA], "Transform Type 3 - Integrity Algorithm Transform
      IDs" section.  Upon receipt of the ROHC_INTEG attribute(s), the
      responder MUST select exactly one of the proposed algorithms; the
      chosen value is sent back in the ROHC_SUPPORTED Notify message
      returned by the responder to the initiator.  The selected
      integrity algorithm MUST be used in both directions.  If the
      responder does not accept any of the algorithms proposed by the
      initiator, ROHC MUST NOT be enabled on the SA.

      It is noted that:

      1.  The keys (one for each direction) for this integrity algorithm
          are derived from the IKEv2 KEYMAT (see [IKEV2], Section 2.17).
          For the purposes of this key derivation, ROHC is considered to

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          be an IPsec protocol.  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
          "IKEv2 Integrity Algorithm Transform IDs" 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

      3.  The ROHC_INTEG attribute is a parameter that is negotiated
          between two ends.  In other words, the initiator indicates
          what it supports, the responder selects one of the ROHC_INTEG
          values proposed and sends the selected value to the initiator.

   ROHC_ICV_LEN (Integrity Algorithm Length, 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 Integrity Check Value (ICV) octets the sender expects to
      receive on incoming ROHC packets.  The ICV of the negotiated
      ROHC_INTEG algorithms MUST be truncated to ROHC_ICV_LEN bytes by
      taking the first ROHC_ICV_LEN bytes of the output.  Both the
      initiator and responder announce a single value 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 the value of
      the ROHC_ICV_LEN attribute is zero, then an ICV MUST NOT be sent.
      If no ROHC_ICV_LEN attribute is sent at all or if 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 MUST
      be sent.

      Note that the ROHC_ICV_LEN attribute is a one-way notification;
      therefore, different values for ROHC_ICV_LEN may be announced in
      each direction.

   MRRU (Maximum Reconstructed Reception Unit, AF = 1)

      The MRRU attribute is an optional attribute.  There MAY be zero or
      one MRRU attribute contained within the ROHC_SUPPORTED Notify
      message.  The attribute value is 2 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 (see Section 5.2.5 of [ROHCV1]).  This size
      includes the Cyclic Redundancy Check (CRC) and the ROHC ICV.  If

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      MRRU is 0 or if no MRRU attribute is sent, segment headers MUST
      NOT be transmitted on the ROHCoIPsec channel.

      Note that the MRRU attribute is a one-way notification; therefore,
      different values for MRRU may be announced in each direction.

   If an unknown ROHC Attribute Type Value is received, it MUST be
   silently ignored.

3.2.  ROHC Channel Parameters That Are Implicitly Set

   The following ROHC channel parameters MUST NOT be signaled:

   o  LARGE_CIDS: This value is implicitly determined by the value of
      MAX_CID (i.e., if MAX_CID is <= 15, LARGE_CIDS is assumed to be

   o  FEEDBACK_FOR: When a pair of SAs is created (one in each
      direction), the ROHC channel parameter FEEDBACK_FOR MUST be set
      implicitly to the other SA of the pair (i.e., the SA pointing in
      the reverse direction).

4.  Security Considerations

   The ability to negotiate the length of the ROHC ICV may introduce
   vulnerabilities to the ROHCoIPsec protocol.  Specifically, the
   capability to signal a short ICV length may result in scenarios where
   erroneous packets are forwarded into the protected domain.  This
   security consideration is documented in further detail in Section
   6.1.4 of [ROHCOIPSEC] and Section 5 of [IPSEC-ROHC].

   This security consideration can be mitigated by using longer ICVs,
   but this comes at the cost of additional overhead, which reduces the
   overall benefits offered by ROHCoIPsec.

5.  IANA Considerations

   This document defines a new Notify message (Status Type).  Therefore,
   IANA has allocated one value from the "IKEv2 Notify Message Types"
   registry to indicate ROHC_SUPPORTED.

   In addition, IANA has created a new "ROHC Attribute Types" registry
   in the "Internet Key Exchange Version 2 (IKEv2) Parameters" registry
   [IKEV2-PARA].  Within the "ROHC Attribute Types" registry, this
   document allocates the following values:

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Value        ROHC Attribute Type                        Format Reference
-----------  --------------------------------------     ------ ---------
0            RESERVED                                          [RFC5857]
1            Maximum Context Identifier (MAX_CID)        TV    [RFC5857]
2            ROHC Profile (ROHC_PROFILE)                 TV    [RFC5857]
3            ROHC Integrity Algorithm (ROHC_INTEG)       TV    [RFC5857]
4            ROHC ICV Length in bytes (ROHC_ICV_LEN)     TV    [RFC5857]
5            Maximum Reconstructed Reception Unit (MRRU) TV    [RFC5857]
6-16383      Unassigned
16384-32767  Private use                                       [RFC5857]

   Following the policies outlined in [IANA-CONSIDERATIONS], the IANA
   policy for assigning new values for the ROHC Attribute Types registry
   shall be Expert Review.

   For registration requests, the responsible IESG Area Director will
   appoint the Designated Expert.  The Designated Expert will post a
   request to both the ROHC and IPsec mailing lists (or a successor
   designated by the Area Director) for comment and review.  The
   Designated Expert will either approve or deny the registration
   request and publish a notice of the decision to both mailing lists
   (or their successors), as well as informing IANA.  A denial notice
   must be justified by an explanation.

6.  Acknowledgments

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

   The authors would also like to thank Yoav Nir and 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  Magnus Westerlund

   o  Stephen Kent

   o  Lars-Erik Jonsson

   o  Pasi Eronen

   o  Jonah Pezeshki

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   o  Carl Knutsson

   o  Joseph Touch

   o  David Black

   o  Glen Zorn

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

7.  References

7.1.  Normative References

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

   [ROHC]       Sandlund, K., Pelletier, G., and L-E. Jonsson, "The
                RObust Header Compression (ROHC) Framework", RFC 5795,
                March 2010.

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

   [BRA97]      Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

   [ROHCV1]     Bormann, C., Burmeister, C., Degermark, M., Fukushima,
                H., Hannu, H., Jonsson, L-E., 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.

   [IPSEC-ROHC] Ertekin, E., Christou, C., and C. Bormann, "IPsec
                Extensions to Support Robust Header Compression over
                IPsec", RFC 5858, May 2010.

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

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7.2.  Informative References

   [ROHCOIPSEC] Ertekin, E., Jasani, R., Christou, C., and C. Bormann,
                "Integration of Header Compression over IPsec Security
                Associations", RFC 5856, May 2010.

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

   [ROHCPROF]   IANA, "RObust Header Compression (ROHC) Profile
                Identifiers", <>.

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

   [IKEV2-PARA] IANA, "Internet Key Exchange Version 2 (KEv2)
                Parameters", <>.

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Authors' Addresses

   Emre Ertekin
   Booz Allen Hamilton
   5220 Pacific Concourse Drive, Suite 200
   Los Angeles, CA  90045


   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
   AuthenTec, Inc.
   Fredrikinkatu 47


   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28334