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

  Integration of Robust Header Compression (ROHC) over IPsec Security
                              Associations
                      draft-ietf-rohc-hcoipsec-10
                      draft-ietf-rohc-hcoipsec-11

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Abstract

   IP Security (IPsec) provides various security services for IP
   traffic.  However, the benefits of IPsec come at the cost of
   increased overhead.  This document outlines a framework for
   integrating Robust Header Compression (ROHC) over IPsec (ROHCoIPsec).
   By compressing the inner headers of IP packets, ROHCoIPsec proposes
   to reduce the amount of overhead associated with the transmission of
   traffic over IPsec Security Associations (SAs).

Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  3  4
   2.      Audience . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
   3.      Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3  4
   4.      Problem Statement: IPsec Packet Overhead . . . . . . . . .  4  5
   5.      Overview of the ROHCoIPsec Framework . . . . . . . . . . .  5  6
   5.1.    ROHCoIPsec Assumptions . . . . . . . . . . . . . . . . . .  5  6
   5.2.    Summary of the ROHCoIPsec Framework  . . . . . . . . . . .  5  6
   6.      Details of the ROHCoIPsec Framework  . . . . . . . . . . .  6  7
   6.1.    ROHC and IPsec Integration . . . . . . . . . . . . . . . .  7  8
   6.1.1.  Header Compression Protocol Considerations . . . . . . . .  9 10
   6.1.2.  Initialization and Negotiation of the ROHC Channel . . . .  9 10
   6.1.3.  Encapsulation and Identification of Header Compressed
           Packets  . . . . . . . . . . . . . . . . . . . . . . . . . 10 11
   6.1.4.  Path MTU Considerations  . . . . . . . . . . . . . . . . . 11
   6.2.    ROHCoIPsec Framework Summary . . . . . . . . . . . . . . . 10 12
   7.      Security Considerations  . . . . . . . . . . . . . . . . . 10 12
   8.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 11 12
   9.      Acknowledgments  . . . . . . . . . . . . . . . . . . . . . 11 12
   10.     Informative References . . . . . . . . . . . . . . . . . . 11 13
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 12 14

1.  Introduction

   This document outlines a framework for integrating ROHC [ROHC] over
   IPsec [IPSEC] (ROHCoIPsec).  The goal of ROHCoIPsec is to reduce the
   protocol overhead associated with packets traversing between IPsec SA
   endpoints.  This can be achieved by compressing the transport layer
   header (e.g., UDP, TCP, etc.) and inner IP header of packets at the
   ingress of the IPsec tunnel, and decompressing these headers at the
   egress.

   For ROHCoIPsec, this document assumes that ROHC will be used to
   compress the inner headers of IP packets traversing an IPsec tunnel.
   However, since current specifications for ROHC detail its operation
   on a hop-by-hop basis, it requires extensions to enable its operation
   over IPsec SAs.  These extensions need to account for increased
   packet reordering and packet loss that may occur in the unprotected
   domain.  This document outlines a framework for extending the usage
   of ROHC to operate at IPsec SA endpoints.

   ROHCoIPsec targets the application of ROHC to tunnel mode SAs.
   Transport mode SAs only encrypt/authenticate the payload of an IP
   packet, leaving the IP header untouched.  Intermediate routers
   subsequently use this IP header to route the packet to a decryption
   device.  Therefore, if ROHC is to operate over IPsec transport-mode
   SAs, (de)compression functionality can only be applied to the
   transport layer headers, and not to the IP header.  Because current
   ROHC specifications do not include support for the compression of
   transport layer headers alone, the ROHCoIPsec framework outlined by
   this document describes the application of ROHC to tunnel mode SAs.

2.  Audience

   The authors target members of both the ROHC and IPsec communities who
   may consider extending the ROHC and IPsec protocols to meet the
   requirements put forth in this document.  In addition, this document
   is directed towards vendors developing IPsec devices that will be
   deployed in bandwidth-constrained IP networks.

3.  Terminology

   Terminology specific to ROHCoIPsec is introduced in this section.

   ROHC Process
      Generic reference to a ROHC instance (as defined in [ROHC-TERM]),
      or any supporting ROHC components.

   Compressed Traffic

      Traffic that is processed through the ROHC compressor and
      decompressor instances.  Packet headers are compressed and
      decompressed using a specific header compression profile.

   Uncompressed Traffic

      Traffic that is not processed by the ROHC compressor instance.
      Instead, this type of traffic bypasses the ROHC process.

   IPsec Process

      Generic reference to the Internet Protocol Security (IPsec)
      process.

   Next Header

      Refers to the Protocol (IPv4) or Next Header (IPv6, Extension)
      field.

4.  Problem Statement: IPsec Packet Overhead

   IPsec mechanisms provide various security services for IP networks.
   However, the benefits of IPsec come at the cost of increased per-
   packet overhead.  For example, traffic flow confidentiality
   (generally leveraged at security gateways) requires the tunneling of
   IP packets between IPsec implementations.  Although these IPsec
   tunnels will effectively mask the source-destination patterns that an
   intruder can ascertain, tunneling comes at the cost of increased per-
   packet overhead.  Specifically, an ESP tunnel mode SA applied to an
   IPv6 flow results in at least 50 bytes of additional overhead per
   packet.  This additional overhead may be undesirable for many
   bandwidth-constrained wireless and/or satellite communications
   networks, as these types of infrastructure are not overprovisioned.
   ROHC applied on a per-hop basis over bandwidth-constrained links will
   also suffer from reduced performance when encryption is used on the
   tunneled header, since encrypted headers cannot be compressed.
   Consequently, the additional overhead incurred by an IPsec tunnel may
   result in the inefficient utilization of bandwidth.

   Packet overhead is particularly significant for traffic profiles
   characterized by small packet payloads (e.g. various voice codecs).
   If these small packets are afforded the security services of an IPsec
   tunnel mode SA, the amount of per-packet overhead is increased.
   Thus, a mechanism is needed to reduce the overhead associated with
   such flows.

5.  Overview of the ROHCoIPsec Framework

5.1.  ROHCoIPsec Assumptions

   The goal of ROHCoIPsec is to provide efficient transport of IP
   packets between IPsec devices without compromising the security
   services offered by IPsec.  The ROHCoIPsec framework has been
   developed based on the following assumptions:
   o  ROHC will be leveraged to reduce the amount of overhead associated
      with packets traversing an IPsec SA
   o  ROHC will be instantiated at the IPsec SA endpoints, and will be
      applied on a per-SA basis
   o  Once the decompression operation completes, decompressed packet
      headers will be identical to the original packet headers before
      compression

5.2.  Summary of the ROHCoIPsec Framework

   ROHC reduces packet overhead in a network by exploiting intra- and
   inter-packet redundancies of network and transport-layer header
   fields of a flow.

   Current ROHC protocol specifications compress packet headers on a
   hop-by-hop basis.  However, IPsec SAs are instantiated between two
   IPsec endpoints.  Therefore, various extensions to both ROHC and
   IPsec need to be defined to ensure the successful operation of the
   ROHC protocol at IPsec SA endpoints.

   The specification of ROHC over IPsec SAs is straightforward, since SA
   endpoints provide source/destination pairs where (de)compression
   operations can take place.  Compression of the inner IP and upper
   layer protocol headers in such a manner offers a reduction of per-
   packet protocol overhead between the two SA endpoints.  Since ROHC
   will now operate between IPsec endpoints (over multiple intermediate
   nodes which are transparent to an IPsec SA), it is imperative to
   ensure that its performance will not be severely impacted due to
   increased packet reordering and/or packet loss between the compressor
   and decompressor.

   In addition, ROHC can no longer rely on the underlying link layer for
   ROHC channel parameter configuration and packet identification.  The
   ROHCoIPsec framework proposes that ROHC channel parameter
   configuration is accomplished by an SA management protocol (e.g.,
   IKEv2 [IKEV2]), while identification of compressed header packets is
   achieved through the Next Header field of the security protocol
   (e.g., AH [AH], ESP [ESP]) header.

   Using the ROHCoIPsec framework proposed below, outbound and inbound
   IP traffic processing at an IPsec device needs to be modified.  For
   an outbound packet, a ROHCoIPsec implementation will compress
   appropriate packet headers, and subsequently encrypt and/or
   integrity-protect the packet.  For tunnel mode SAs, compression may
   be applied to the transport layer and the inner IP headers.  For
   inbound packets, an IPsec device must first decrypt and/or integrity-
   check the packet.  Then decompression of the inner packet headers is
   performed.  After decompression, the packet is checked against the
   access controls imposed on all inbound traffic associated with the SA
   (as specified in [IPSEC]).

      Note: Compression of inner headers is independent from compression
      of the security protocol (e.g., ESP) and outer IP headers.  ROHC
      profiles have been defined to allow for the compression of the
      security protocol and the outer IP header on a hop-by-hop basis.
      The applicability of ROHCoIPsec and hop-by-hop ROHC on an IPv4
      ESP-processed packet [ESP] is shown below in Figure 1.

             -----------------------------------------------------------
       IPv4  | new IP hdr  |     | orig IP hdr   |   |    | ESP   | ESP|
             |(any options)| ESP | (any options) |TCP|Data|Trailer| ICV|
             -----------------------------------------------------------
             |<-------(1)------->|<------(2)-------->|

             (1) Compressed by ROHC ESP/IP profile
             (2) Compressed by ROHCoIPsec TCP/IP profile

      Figure 1.  Applicability of hop-by-hop ROHC and ROHCoIPsec on an
      IPv4 ESP-processed packet.

   If IPsec NULL encryption is applied to packets, ROHC may still be
   applied to the inner headers at the IPsec SA endpoints.  However,
   this poses challenges for intermediary devices (within the
   unprotected domain) inspecting ESP-NULL encrypted packets, since
   these intermediary devices will require additional functionality to
   determine the content of the ROHC packets.

6.  Details of the ROHCoIPsec Framework

6.1.  ROHC and IPsec Integration

   Figure 2 illustrates the components required to integrate ROHC with
   the IPsec process, i.e., ROHCoIPsec.

                  +-------------------------------+
                  | ROHC Module                   |
                  |                               |
                  |                               |
        +-----+   |     +-----+     +---------+   |
        |     |   |     |     |     |  ROHC   |   |
      --|  A  |---------|  B  |-----| Process |------> Path 1
        |     |   |     |     |     |         |   |   (ROHC-enabled SA)
        +-----+   |     +-----+     +---------+   |
           |      |        |                      |
           |      |        |-------------------------> Path 2
           |      |                               |   (ROHC-enabled SA)
           |      +-------------------------------+
           |
           |
           |
           |
           +-----------------------------------------> Path 3
                                                      (ROHC-disabled SA)

                Figure 2.  Integration of ROHC with IPsec.

   The process illustrated in Figure 2 augments the IPsec processing
   model for outbound IP traffic (protected-to-unprotected).  Initial
   IPsec processing is consistent with [IPSEC] (Steps 1-2, Section 5.1).

   Block A: The ROHC data item (part of the SA state information)
   retrieved from the "relevant SAD entry" ([IPSEC], Section 5.1,
   Step3a) determines if the traffic traversing the SA is handed to the
   ROHC module.  Packets selected to a ROHC-disabled SA must follow
   normal IPsec processing and must not be sent to the ROHC module
   (Figure 1, Path 3).  Conversely, packets selected to a ROHC-enabled
   SA must be sent to the ROHC module.

   Block B: This step determines if the packet can be compressed.  If it
   is determined that the packet will be compressed, an Integrity
   Algorithm may be used to compute an Integrity Check Value (ICV) for
   the uncompressed packet ([IPSEC-ROHC], Section 3.2 [IKE-ROHC],
   Section 2.1).  The Next Header field of the security protocol header
   (e.g., ESP, AH) is populated with a "ROHC" identifier, protocol number
   [PROTOCOL], inner packet headers are compressed, and the computed ICV
   ICV, if present, is appended to the packet (Figure 1, Path 1).

   However, if it is determined that the packet will not be compressed
   (e.g., due to one the reasons described in Section 6.1.3), the Next
   Header field is populated with the appropriate value indicating the
   next level protocol (Figure 1, Path
   2). 2), and no ROHC processing is
   applied to the packet.

   After the ROHC process completes, IPsec processing resumes, as
   described in Section 5.1, Step3a, of [IPSEC].

   The process illustrated in Figure 2 also augments the IPsec
   processing model for inbound IP traffic (unprotected-to-protected).
   For inbound packets, IPsec processing is performed ([IPSEC], Section
   5.2, Steps 1-3) followed by AH or ESP processing ([IPSEC], Section
   5.2, Step 4).

   Block A: After AH or ESP processing, the ROHC data item retrieved
   from the SAD entry will indicate if traffic traversing the SA is
   processed by the ROHC module ([IPSEC], Section 5.2, Step 3a).
   Packets traversing an ROHC-disabled SA must follow normal IPsec
   processing and must not be sent to the ROHC module.  Conversely,
   packets traversing an ROHC-enabled SA must be sent to the ROHC
   module.

   Block B: The decision at Block B is determined by the value of the
   Next Header field of the security protocol header.  If the Next
   Header field does not indicate a ROHC header, the decompressor must
   not attempt decompression (Figure 1, Path 2).  If the Next Header
   field indicates a ROHC header, decompression is applied.  After
   decompression, the signaled ROHCoIPsec Integrity Algorithm Algorithm, if
   present, is used to compute an ICV value for the decompressed packet.
   This ICV ICV, if present, is compared to the ICV that was calculated at
   the compressor: if the ICVs match, the packet is forwarded by the
   ROHC module (Figure 1, Path 1); otherwise, the packet is dropped.
   Once the ROHC module completes processing, IPsec processing resumes,
   as described in Section 5.2, Step 4 of [IPSEC].

   When there is a single SA between a compressor and decompressor, ROHC
   operates in unidirectional mode, as described in Section 5 of [ROHC-
   TERM].  When there is pair of SAs instantiated between ROHCoIPsec
   implementations, ROHC may operate in bidirectional mode, where an SA
   pair represents a bidirectional ROHC channel (as described in Section
   6.1 and 6.2 of [ROHC-TERM]).

   Note that to further reduce the size of an IPsec-protected packet,
   ROHCoIPsec and IPcomp [IPCOMP] can be implemented in a nested
   fashion.  This process is detailed in [IPSEC-ROHC], Section 3.2.

6.1.1.  Header Compression Protocol Considerations

   ROHCv2 [ROHCV2] profiles include various mechanisms that provide
   increased robustness over reordering channels.  These mechanisms must
   be adopted for ROHC to operate efficiently over IPsec SAs.

   A ROHC decompressor implemented within IPsec architecture may
   leverage additional mechanisms to improve performance over reordering
   channels (either due to random events, or to an attacker
   intentionally reordering packets).  Specifically, IPsec's sequence
   number may be used by the decompressor to identify a packet as
   "sequentially late".  This knowledge will increase the likelihood of
   successful decompression of a reordered packet.

   Additionally, ROHCoIPsec implementations should minimize the amount
   of feedback sent from the decompressor to the compressor.  If a ROHC
   feedback channel is not used sparingly, the overall gains from
   ROHCoIPsec can be significantly reduced.  More specifically, any
   feedback sent from the decompressor to the compressor must be
   processed by IPsec, and tunneled back to the compressor (as
   designated by the SA associated with FEEDBACK_FOR).  As such, some
   implementation alternatives can be considered, including the
   following:
   o  Eliminate feedback traffic altogether by operating only in ROHC
      Unidirectional mode (U-mode)
   o  Piggyback ROHC feedback messages within the feedback element
      (i.e., on ROHC traffic that normally traverses the SA designated
      by FEEDBACK_FOR. FEEDBACK_FOR).

6.1.2.  Initialization and Negotiation of the ROHC Channel

   Hop-by-hop ROHC typically uses the underlying link layer (e.g., PPP)
   to negotiate ROHC channel parameters.  In the case of ROHCoIPsec,
   channel parameters can be set manually (i.e., administratively
   configured for manual SAs), or negotiated by IKEv2.  The extensions
   required for IKEv2 to support ROHC channel parameter negotiation are
   detailed in [IKE-ROHC].

   If the ROHC protocol requires bidirectional communications, two SAs
   must be instantiated between the IPsec implementations.  One of the
   two SAs is used for carrying ROHC-traffic from the compressor to the
   decompressor, while the other is used to communicate ROHC-feedback
   from the decompressor to the compressor.  Note that the requirement
   for two SAs aligns with the operation of IKE, which creates SAs in
   pairs by default.  However, IPsec implementations will dictate how
   decompressor feedback received on one SA is associated with a
   compressor on the other SA.  An IPsec implementation must relay the
   feedback received by the decompressor on an inbound SA to the
   compressor associated with the corresponding outbound SA.

6.1.3.  Encapsulation and Identification of Header Compressed Packets

   As indicated in Section 6.1, new state information (i.e., a new ROHC
   data item) is defined for each SA.  The ROHC data item is used by the
   IPsec process to determine whether it sends all traffic traversing a
   given SA to the ROHC module (ROHC-enabled) or bypasses the ROHC
   module and sends the traffic through regular IPsec processing (ROHC-
   disabled).

   The Next Header field of the IPsec security protocol (e.g., AH or
   ESP) header is used to demultiplex header-compressed traffic from
   uncompressed traffic traversing an ROHC-enabled SA.  This
   functionality is needed in situations where packets traversing a
   ROHC-enabled SA contain uncompressed headers.  Such situations may
   occur when, for example, a compressor supports strictly n compressed
   flows and cannot compress the n+1 flow that arrives.  Another example
   is when traffic is selected to a ROHC-enabled SA, but cannot be
   compressed by the ROHC process because the appropriate ROHC Profile
   has not been signaled for use.  As a result, the decompressor must be
   able to identify packets with uncompressed headers and not attempt to
   decompress them.  The Next Header field is used to demultiplex these
   header-compressed and uncompressed packets where the ROHC protocol
   identifier
   number will indicate that the packet contains compressed headers.  To
   accomplish this, an official IANA allocation from the Protocol ID
   registry [PROTOCOL] is required.

   The ROHC Data Item, IANA Protocol ID allocation, and other IPsec
   extensions to support ROHCoIPsec, are specified in [IPSEC-ROHC].

6.1.4.  Path MTU Considerations

   By encapsulating IP packets with AH/ESP and tunneling IP headers,
   IPsec increases the size of IP packets.  This increase may result in
   Path MTU issues in the unprotected domain.  Several approaches to
   resolving these path MTU issues are documented in Section 8 of
   [IPSEC]; approaches include fragmenting the packet before or after
   IPsec processing (if the packet's DF bit is clear), or possibly
   discarding packets (if the packet's DF bit is set).

   The addition of ROHC within the IPsec processing model may result in
   a similar path MTU challenges.  For example, under certain
   circumstances, ROHC headers are larger than the original uncompressed
   headers.  In addition, if an integrity algorithm is used to validate
   packet headers post-decompression, this integrity algorithm will
   increase the size of packets.  Both of these properties of ROHCoIPsec
   increase the size of packets, and therefore may result in additional
   challenges associated with path MTU.

   Approaches to addressing these ROHCoIPsec path MTU issues are
   specified in Section 3.3 of [IPSEC-ROHC].

6.2.  ROHCoIPsec Framework Summary

   To summarize, the following items are needed to achieve ROHCoIPsec:
   o  IKEv2 Extensions to Support ROHCoIPsec
   o  IPsec Extensions to Support ROHCoIPsec

7.  Security Considerations

   A malfunctioning ROHC compressor (i.e., the compressor located at the
   ingress of the IPsec tunnel) has the ability to send packets to the
   decompressor (i.e., the decompressor located at the egress of the
   IPsec tunnel) that do not match the original packets emitted from the
   end-hosts.  Such a scenario will result in a decreased efficiency
   between compressor and decompressor.  Furthermore, this may result in
   Denial of Service, as the decompression of a significant number of
   invalid packets may drain the resources of an IPsec device.

8.  IANA Considerations

   None.

9.  Acknowledgments

   The authors would like to thank Mr. Sean O'Keeffe, Mr. James Kohler,
   and Ms. Linda Noone of the Department of Defense, and 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
   specification.

   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. Pasi Eronen
   o  Dr. Joseph Touch
   o  Mr. Tero Kivinen
   o  Dr. Jonah Pezeshki
   o  Mr. Lars-Erik Jonsson
   o  Mr. Jan Vilhuber
   o  Mr. Dan Wing
   o  Mr. Kristopher Sandlund
   o  Mr. Ghyslain Pelletier

   Finally, the authors would also like to thank Mr. Tom Conkle, Ms.
   Renee Esposito, Mr. Etzel Brower, and Ms. Michele Casey of Booz Allen
   Hamilton for their assistance in completing this work.

10.  Informative References

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

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

   [ROHC-TERM]
              Jonsson, L-E., "Robust Header Compression (ROHC):
              Terminology and Channel Mapping Examples", RFC 3759,
              April 2004.

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

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

   [AH]       Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.

   [IPCOMP]   Shacham, A., Monsour, R., Pereira, and Thomas, "IP Payload
              Compression Protocol (IPComp)", RFC 3173, September 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.

   [IKE-ROHC]
              Ertekin, E., Christou, C., Jasani, R., Kivinen, T., and C.
              Bormann, "IKEv2 Extensions to Support ROHCoIPsec", work in
              progress , February August 2009.

   [PROTOCOL]
              IANA, "Assigned Internet Protocol Numbers, IANA registry
              at: http://www.iana.org/assignments/protocol-numbers".

   [IPSEC-ROHC]
              Ertekin, E., Christou, C., and C. Bormann, "IPsec
              Extensions to Support ROHCoIPsec", work in progress ,
              February
              August 2009.

Authors' Addresses

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

   Email: ertekin_emre@bah.com

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

   Email: jasani_rohan@bah.com ro@breakcheck.com

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

   Email: christou_chris@bah.com

   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28334
   Germany

   Email: cabo@tzi.org