Internet Engineering Task Force (IETF) E. Ertekin
Request for Comments: 5857 C. Christou
Category: Standards Track R. Jasani
ISSN: 2070-1721 Booz Allen Hamilton
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.
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Table of Contents
1. Introduction ....................................................32. Terminology .....................................................33. ROHC Channel Initialization for ROHCoIPsec ......................33.1. ROHC_SUPPORTED Notify Message ..............................33.1.1. ROHC Attributes .....................................53.1.2. ROHC Attribute Types ................................63.2. ROHC Channel Parameters That Are Implicitly Set ............94. Security Considerations .........................................95. IANA Considerations .............................................96. Acknowledgments ................................................107. References .....................................................117.1. Normative References ......................................117.2. Informative References ....................................12
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.
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 [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.
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
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.
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.
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,
ROHC_PROFILE, ROHC_INTEG, ROHC_ICV_LEN, and MRRU. The value
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.
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
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
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
Note that the ROHC_ICV_LEN attribute is a one-way notification;
therefore, different values for ROHC_ICV_LEN may be announced in
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
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
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:
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]
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.
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
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.
7.1. 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,
[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,
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