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Internet Engineering Task Force (IETF)                         K. GrewalRequest for Comments: 5840                             Intel CorporationCategory: Standards Track                                  G. MontenegroISSN: 2070-1721                                    Microsoft Corporation                                                               M. Bhatia                                                          Alcatel-Lucent                                                              April 2010Wrapped Encapsulating Security Payload (ESP) for Traffic VisibilityAbstract   This document describes the Wrapped Encapsulating Security Payload   (WESP) protocol, which builds on the Encapsulating Security Payload   (ESP)RFC 4303 and is designed to allow intermediate devices to (1)   ascertain if data confidentiality is being employed within ESP, and   if not, (2) inspect the IPsec packets for network monitoring and   access control functions.  Currently, in the IPsec ESP standard,   there is no deterministic way to differentiate between encrypted and   unencrypted payloads by simply examining a packet.  This poses   certain challenges to the intermediate devices that need to deep   inspect the packet before making a decision on what should be done   with that packet (Inspect and/or Allow/Drop).  The mechanism   described in this document can be used to easily disambiguate   integrity-only ESP from ESP-encrypted packets, without compromising   on the security provided by ESP.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5840.Grewal, et al.               Standards Track                    [Page 1]

RFC 5840               WESP for Traffic Visibility            April 2010Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) 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 Contents1. Introduction ....................................................31.1. Requirements Language ......................................41.2. Applicability Statement ....................................42. Wrapped ESP (WESP) Header Format ................................52.1. UDP Encapsulation ..........................................82.2. Transport and Tunnel Mode Considerations ...................92.2.1. Transport Mode Processing ...........................92.2.2. Tunnel Mode Processing .............................102.3. IKE Considerations ........................................113. Security Considerations ........................................124. IANA Considerations ............................................135. Acknowledgments ................................................136. References .....................................................146.1. Normative References ......................................146.2. Informative References ....................................14Grewal, et al.               Standards Track                    [Page 2]

RFC 5840               WESP for Traffic Visibility            April 20101.  Introduction   Use of ESP within IPsec [RFC4303] specifies how ESP packet   encapsulation is performed.  It also specifies that ESP can provide   data confidentiality and data integrity services.  Data integrity   without data confidentiality ("integrity-only ESP") is possible via   the ESP-NULL encryption algorithm [RFC2410] or via combined-mode   algorithms such as AES-GMAC [RFC4543].  The exact encapsulation and   algorithms employed are negotiated out of band using, for example,   Internet Key Exchange Protocol version 2 (IKEv2) [RFC4306] and based   on policy.   Enterprise environments typically employ numerous security policies   (and tools for enforcing them), as related to access control, content   screening, firewalls, network monitoring functions, deep packet   inspection, Intrusion Detection and Prevention Systems (IDS and IPS),   scanning and detection of viruses and worms, etc.  In order to   enforce these policies, network tools and intermediate devices   require visibility into packets, ranging from simple packet header   inspection to deeper payload examination.  Network security protocols   that encrypt the data in transit prevent these network tools from   performing the aforementioned functions.   When employing IPsec within an enterprise environment, it is   desirable to employ ESP instead of Authentication Header (AH)   [RFC4302], as AH does not work in NAT environments.  Furthermore, in   order to preserve the above network monitoring functions, it is   desirable to use integrity-only ESP.  In a mixed-mode environment,   some packets containing sensitive data employ a given encryption   cipher suite, while other packets employ integrity-only ESP.  For an   intermediate device to unambiguously distinguish which packets are   using integrity-only ESP requires knowledge of all the policies being   employed for each protected session.  This is clearly not practical.   Heuristics-based methods can be employed to parse the packets, but   these can be very expensive, requiring numerous rules based on each   different protocol and payload.  Even then, the parsing may not be   robust in cases where fields within a given encrypted packet happen   to resemble the fields for a given protocol or heuristic rule.  In   cases where the packets may be encrypted, it is also wasteful to   check against heuristics-based rules, when a simple exception policy   (e.g., allow, drop, or redirect) can be employed to handle the   encrypted packets.  Because of the non-deterministic nature of   heuristics-based rules for disambiguating between encrypted and non-   encrypted data, an alternative method for enabling intermediate   devices to function in encrypted data environments needs to be   defined.  Additionally, there are many types and classes of network   devices employed within a given network and a deterministic approach   provides a simple solution for all of them.  Enterprise environmentsGrewal, et al.               Standards Track                    [Page 3]

RFC 5840               WESP for Traffic Visibility            April 2010   typically use both stateful and stateless packet inspection   mechanisms.  The previous considerations weigh particularly heavy on   stateless mechanisms such as router Access Control Lists (ACLs) and   NetFlow exporters.  Nevertheless, a deterministic approach provides a   simple solution for the myriad types of devices employed within a   network, regardless of their stateful or stateless nature.   This document defines a mechanism to provide additional information   in relevant IPsec packets so intermediate devices can efficiently   differentiate between encrypted and integrity-only packets.   Additionally, and in the interest of consistency, this extended   format can also be used to carry encrypted packets without loss in   disambiguation.   This document is consistent with the operation of ESP in NAT   environments [RFC3947].   The design principles for this protocol are the following:   o  Allow easy identification and parsing of integrity-only IPsec      traffic   o  Leverage the existing hardware IPsec parsing engines as much as      possible to minimize additional hardware design costs   o  Minimize the packet overhead in the common case1.1.  Requirements Language   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 inRFC 2119 [RFC2119].1.2.  Applicability Statement   The document is applicable only to the wrapped ESP header defined   below, and does not describe any changes to either ESP [RFC4303] or   the IP Authentication Header (AH) [RFC4302].   There are two well-accepted ways to enable intermediate security   devices to distinguish between encrypted and unencrypted ESP traffic:   - The heuristics approach [Heuristics] has the intermediate node     inspect the unchanged ESP traffic, to determine with extremely high     probability whether or not the traffic stream is encrypted.Grewal, et al.               Standards Track                    [Page 4]

RFC 5840               WESP for Traffic Visibility            April 2010   - The Wrapped ESP (WESP) approach, described in this document, in     contrast, requires the ESP endpoints to be modified to support the     new protocol.  WESP allows the intermediate node to distinguish     encrypted and unencrypted traffic deterministically, using a     simpler implementation for the intermediate node.   Both approaches are being documented simultaneously by the IP   Security Maintenance and Extensions (IPsecME) Working Group, with   WESP (this document) as a Standards Track RFC while the heuristics   approach is expected to be published as an Informational RFC.  While   endpoints are being modified to adopt WESP, we expect both approaches   to coexist for years because the heuristic approach is needed to   inspect traffic where at least one of the endpoints has not been   modified.  In other words, intermediate nodes are expected to support   both approaches in order to achieve good security and performance   during the transition period.2.  Wrapped ESP (WESP) Header Format   Wrapped ESP (WESP) encapsulation uses protocol number 141.   Accordingly, the (outer) protocol header (IPv4, IPv6, or Extension)   that immediately precedes the WESP header SHALL contain the value   (141) in its Protocol (IPv4) or Next Header (IPv6, Extension) field.   WESP provides additional attributes in each packet to assist in   differentiating between encrypted and non-encrypted data, and to aid   in parsing of the packet.  WESP followsRFC 4303 for all IPv6 and   IPv4 considerations (e.g., alignment considerations).   This extension essentially acts as a wrapper to the existing ESP   protocol and provides an additional 4 octets at the front of the   existing ESP packet for IPv4.  For IPv6, additional padding may be   required and this is described below.   The packet format may be depicted as follows:       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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                       Wrapped ESP Header                      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                      Existing ESP Encapsulation               |      ~                                                               ~      |                                                               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                         Figure 1: WESP Packet FormatGrewal, et al.               Standards Track                    [Page 5]

RFC 5840               WESP for Traffic Visibility            April 2010   By preserving the body of the existing ESP packet format, a compliant   implementation can simply add in the new header, without needing to   change the body of the packet.  The value of the new protocol used to   identify this new header is 141.  Further details are shown below:       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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  Next Header  |   HdrLen      |  TrailerLen   |     Flags     |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                       Padding (optional)                      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                      Existing ESP Encapsulation               |      ~                                                               ~      |                                                               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    Figure 2: Detailed WESP Packet Format   Where:   Next Header, 8 bits: This field MUST be the same as the Next Header   field in the ESP trailer when using ESP in the Integrity-only mode.   When using ESP with encryption, the "Next Header" field looses this   name and semantics and becomes an empty field that MUST be   initialized to all zeros.  The receiver MUST do some sanity checks   before the WESP packet is accepted.  The receiver MUST ensure that   the Next Header field in the WESP header and the Next Header field in   the ESP trailer match when using ESP in the Integrity-only mode.  The   packet MUST be dropped if the two do not match.  Similarly, the   receiver MUST ensure that the Next Header field in the WESP header is   an empty field initialized to zero if using WESP with encryption.   The WESP flags dictate if the packet is encrypted.   HdrLen, 8 bits: Offset from the beginning of the WESP header to the   beginning of the Rest of Payload Data (i.e., past the IV, if present   and any other WESP options defined in the future) within the   encapsulated ESP header, in octets.  HdrLen MUST be set to zero when   using ESP with encryption.  When using integrity-only ESP, the   following HdrLen values are invalid: any value less than 12; any   value that is not a multiple of 4; any value that is not a multiple   of 8 when using IPv6.  The receiver MUST ensure that this field   matches with the header offset computed from using the negotiated   Security Association (SA) and MUST drop the packet in case it does   not match.Grewal, et al.               Standards Track                    [Page 6]

RFC 5840               WESP for Traffic Visibility            April 2010   TrailerLen, 8 bits: TrailerLen contains the size of the Integrity   Check Value (ICV) being used by the negotiated algorithms within the   IPsec SA, in octets.  TrailerLen MUST be set to zero when using ESP   with encryption.  The receiver MUST only accept the packet if this   field matches with the value computed from using the negotiated SA.   This ensures that sender is not deliberately setting this value to   obfuscate a part of the payload from examination by a trusted   intermediary device.   Flags, 8 bits: The bits are defined most-significant-bit (MSB) first,   so bit 0 is the most significant bit of the flags octet.       0 1 2 3 4 5 6 7      +-+-+-+-+-+-+-+-+      |V V|E|P| Rsvd  |      +-+-+-+-+-+-+-+-+      Figure 3: Flags Format   Version (V), 2 bits: MUST be sent as 0 and checked by the receiver.   If the version is different than an expected version number (e.g.,   negotiated via the control channel), then the packet MUST be dropped   by the receiver.  Future modifications to the WESP header require a   new version number.  In particular, the version of WESP defined in   this document does not allow for any extensions.  However, old   implementations will still be able to find the encapsulated cleartext   packet using the HdrLen field from the WESP header, when the 'E' bit   is not set.  Intermediate nodes dealing with unknown versions are not   necessarily able to parse the packet correctly.  Intermediate   treatment of such packets is policy dependent (e.g., it may dictate   dropping such packets).   Encrypted Payload (E), 1 bit: Setting the Encrypted Payload bit to 1   indicates that the WESP (and therefore ESP) payload is protected with   encryption.  If this bit is set to 0, then the payload is using   integrity-only ESP.  Setting or clearing this bit also impacts the   value in the WESP Next Header field, as described above.  The   recipient MUST ensure consistency of this flag with the negotiated   policy and MUST drop the incoming packet otherwise.   Padding header (P), 1 bit: If set (value 1), the 4-octet padding is   present.  If not set (value 0), the 4-octet padding is absent.  This   padding MUST be used with IPv6 in order to preserve IPv6 8-octet   alignment.  If WESP is being used with UDP encapsulation (seeSection2.1 below) and IPv6, the Protocol Identifier (0x00000002) occupies 4   octets so the IPv6 padding is not needed, as the header is already on   an 8-octet boundary.  This padding MUST NOT be used with IPv4, as it   is not needed to guarantee 4-octet IPv4 alignment.Grewal, et al.               Standards Track                    [Page 7]

RFC 5840               WESP for Traffic Visibility            April 2010   Rsvd, 4 bits: Reserved for future use.  The reserved bits MUST be   sent as 0, and ignored by the receiver.  Future documents defining   any of these bits MUST NOT affect the distinction between encrypted   and unencrypted packets or the semantics of HdrLen.  In other words,   even if new bits are defined, old implementations will be able to   find the encapsulated packet correctly.  Intermediate nodes dealing   with unknown reserved bits are not necessarily able to parse the   packet correctly.  Intermediate treatment of such packets is policy   dependent (e.g., it may dictate dropping such packets).   Future versions of this protocol may change the version number and/or   the reserved bits sent, possibly by negotiating them over the control   channel.   As can be seen, the WESP format extends the standard ESP header by   the first 4 octets for IPv4 and optionally (see above) by 8 octets   for IPv6.2.1.  UDP Encapsulation   This section describes a mechanism for running the new packet format   over the existing UDP encapsulation of ESP as defined inRFC 3948.   This allows leveraging the existing IKE negotiation of the UDP port   for Network Address Translation Traversal (NAT-T) discovery and usage   [RFC3947] [RFC4306], as well as preserving the existing UDP ports for   ESP (port 4500).  With UDP encapsulation, the packet format can be   depicted as follows.       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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |        Src Port (4500)        | Dest Port (4500)              |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |             Length            |          Checksum             |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |          Protocol Identifier (value = 0x00000002)             |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  Next Header  |   HdrLen      |  TrailerLen   |    Flags      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                      Existing ESP Encapsulation               |      ~                                                               ~      |                                                               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                    Figure 4: UDP-Encapsulated WESP HeaderGrewal, et al.               Standards Track                    [Page 8]

RFC 5840               WESP for Traffic Visibility            April 2010   Where:   Source/Destination port (4500) and checksum: describes the UDP   encapsulation header, perRFC 3948.   Protocol Identifier: new field to demultiplex between UDP   encapsulation of IKE, UDP encapsulation of ESP perRFC 3948, and the   UDP encapsulation in this specification.   According toRFC 3948, Section 2.2, a 4-octet value of zero (0)   immediately following the UDP header indicates a Non-ESP marker,   which can be used to assume that the data following that value is an   IKE packet.  Similarly, a value greater then 255 indicates that the   packet is an ESP packet and the 4-octet value can be treated as the   ESP Security Parameter Index (SPI).  However,RFC 4303, Section 2.1   indicates that the values 1-255 are reserved and cannot be used as   the SPI.  We leverage that knowledge and use one of these reserved   values to indicate that the UDP encapsulated ESP header contains this   new packet format for ESP encapsulation.   The remaining fields in the packet have the same meaning as perSection 2 above.2.2.  Transport and Tunnel Mode Considerations   This extension is equally applicable to transport and tunnel mode   where the ESP Next Header field is used to differentiate between   these modes, as per the existing IPsec specifications.2.2.1.  Transport Mode Processing   In transport mode, ESP is inserted after the IP header and before a   next layer protocol, e.g., TCP, UDP, ICMP, etc.  The following   diagrams illustrate how WESP is applied to the ESP transport mode for   a typical packet, on a "before and after" basis.Grewal, et al.               Standards Track                    [Page 9]

RFC 5840               WESP for Traffic Visibility            April 2010      BEFORE APPLYING WESP -IPv4            -------------------------------------------------            |orig IP hdr  | ESP |     |      |   ESP   | ESP|            |(any options)| Hdr | TCP | Data | Trailer | ICV|            -------------------------------------------------                                |<---- encryption ---->|                          |<------- integrity -------->|      AFTER APPLYING WESP - IPv4            --------------------------------------------------------            |orig IP hdr  | WESP | ESP |     |      |   ESP   | ESP|            |(any options)| Hdr  | Hdr | TCP | Data | Trailer | ICV|            --------------------------------------------------------                                       |<---- encryption ---->|                                 |<------- integrity -------->|      BEFORE APPLYING WESP - IPv6          --------------------------------------------------------------          | orig |hop-by-hop,dest*,|   |dest|   |    | ESP   | ESP|          |IP hdr|routing,fragment |ESP|opt*|TCP|Data|Trailer| ICV|          --------------------------------------------------------------                                       |<---- encryption --->|                                   |<----- integrity ------->|      AFTER APPLYING WESP - IPv6          --------------------------------------------------------------          | orig |hop-by-hop,dest*,|    |   |dest|   |    | ESP   | ESP|          |IP hdr|routing,fragment |WESP|ESP|opt*|TCP|Data|Trailer| ICV|          --------------------------------------------------------------                                            |<---- encryption --->|                                        |<----- integrity ------->|          * = if present, could be before WESP, after ESP, or both    All other considerations are as perRFC 4303.2.2.2.  Tunnel Mode Processing   In tunnel mode, ESP is inserted after the new IP header and before   the original IP header, as perRFC 4303.  The following diagram   illustrates how WESP is applied to the ESP tunnel mode for a typical   packet, on a "before-and-after" basis.Grewal, et al.               Standards Track                   [Page 10]

RFC 5840               WESP for Traffic Visibility            April 2010      BEFORE APPLYING WESP - IPv4          ---------------------------------------------------------          |new IP hdr*  |   | orig IP hdr*  |   |    | ESP   | ESP|          |(any options)|ESP| (any options) |TCP|Data|Trailer| ICV|          ---------------------------------------------------------                            |<--------- encryption --------->|                        |<----------- integrity ------------>|      AFTER APPLYING WESP - IPv4          --------------------------------------------------------------          |new IP hdr*  |    |   | orig IP hdr*  |   |    | ESP   | ESP|          |(any options)|WESP|ESP| (any options) |TCP|Data|Trailer| ICV|          --------------------------------------------------------------                                 |<--------- encryption --------->|                             |<----------- integrity ------------>|      BEFORE APPLYING WESP - IPv6      -----------------------------------------------------------------      |new IP|new ext |   |orig IP|orig ext|   |    | ESP   | ESP|      | hdr* | hdrs*  |ESP|  hdr* | hdrs * |TCP|Data|Trailer| ICV|      -----------------------------------------------------------------                          |<--------- encryption ---------->|                      |<------------- integrity ----------->|      AFTER APPLYING WESP - IPv6      -----------------------------------------------------------------      |new IP|new ext |    |   |orig IP|orig ext|   |    | ESP   | ESP|      | hdr* | hdrs*  |WESP|ESP|  hdr* | hdrs * |TCP|Data|Trailer| ICV|      -----------------------------------------------------------------                               |<--------- encryption ---------->|                           |<------------- integrity ----------->|          * = if present, construction of outer IP hdr/extensions and              modification of inner IP hdr/extensions is discussed in              the Security Architecture document.   All other considerations are as perRFC 4303.2.3.  IKE Considerations   This document assumes that WESP negotiation is performed using IKEv2.   In order to negotiate the new format of ESP encapsulation via IKEv2   [RFC4306], both parties need to agree to use the new packet format.   This can be achieved using a notification method similar to   USE_TRANSPORT_MODE, defined inRFC 4306.Grewal, et al.               Standards Track                   [Page 11]

RFC 5840               WESP for Traffic Visibility            April 2010   The notification, USE_WESP_MODE (value 16415) MUST be included in a   request message that also includes an SA payload requesting a   CHILD_SA using ESP.  It signals that the sender supports the WESP   version defined in the current document and requests that the   CHILD_SA use WESP mode rather than ESP for the SA created.  If the   request is accepted, the response MUST also include a notification of   type USE_WESP_MODE.  If the responder declines the request, the   CHILD_SA will be established using ESP, as perRFC 4303.  If this is   unacceptable to the initiator, the initiator MUST delete the SA.   Note: Except when using this option to negotiate WESP mode, all   CHILD_SAs will use standard ESP.   Negotiation of WESP in this manner preserves all other negotiation   parameters, including NAT-T [RFC3948].  NAT-T is wholly compatible   with this wrapped format and can be used as-is, without any   modifications, in environments where NAT is present and needs to be   taken into account.   WESP version negotiation is not introduced as part of this   specification.  If the WESP version is updated in a future   specification, then that document MUST specify how the WESP version   is negotiated.3.  Security Considerations   As this document augments the existing ESP encapsulation format, UDP   encapsulation definitions specified inRFC 3948 and IKE negotiation   of the new encapsulation, the security observations made in those   documents also apply here.  In addition, as this document allows   intermediate device visibility into IPsec ESP encapsulated frames for   the purposes of network monitoring functions, care should be taken   not to send sensitive data over connections using definitions from   this document, based on network domain/administrative policy.  A   strong key agreement protocol, such as IKEv2, together with a strong   policy engine should be used in determining appropriate security   policy for the given traffic streams and data over which it is being   employed.   ESP is end-to-end and it will be impossible for the intermediate   devices to verify that all the fields in the WESP header are correct.   It is thus possible to modify the WESP header so that the packet   sneaks past a firewall if the fields in the WESP header are set to   something that the firewall will allow.  The endpoint thus must   verify the sanity of the WESP header before accepting the packet.  In   an extreme case, someone colluding with the attacker, could changeGrewal, et al.               Standards Track                   [Page 12]

RFC 5840               WESP for Traffic Visibility            April 2010   the WESP fields back to the original values so that the attack goes   unnoticed.  However, this is not a new problem and it already exists   IPsec.4.  IANA Considerations   The WESP protocol number assigned by IANA out of the IP Protocol   Number space is 141.   The USE_WESP_MODE notification number assigned out of the "IKEv2   Notify Message Types - Status Types" registry's 16384-40959 (Expert   Review) range is 16415.   The SPI value of 2 has been assigned by IANA out of the reserved SPI   range from the SPI values registry to indicate use of the WESP   protocol within a UDP-encapsulated, NAT-T environment.   IANA has created a new registry for "WESP Flags" to be managed as   follows:   The first 2 bits are the WESP Version Number.  The value 0 is   assigned to the version defined in this specification.  Further   assignments of the WESP Version Number are to be managed via the IANA   Policy of "Standards Action" [RFC5226].  For WESP version numbers,   the unassigned values are 1, 2, and 3.  The Encrypted Payload bit is   used to indicate if the payload is encrypted or using integrity-only   ESP.  The Padding Present bit is used to signal the presence of   padding.  The remaining 4 bits of the WESP Flags are undefined and   future assignment is to be managed via the IANA Policy of "IETF   Review" [RFC5226].5.  Acknowledgments   The authors would like to acknowledge the following people for their   feedback on updating the definitions in this document:   David McGrew, Brian Weis, Philippe Joubert, Brian Swander, Yaron   Sheffer, Pasi Eronen, Men Long, David Durham, Prashant Dewan, Marc   Millier, Russ Housley, and Jari Arkko, among others.   Manav Bhatia would also like to acknowledge Swati and Maitri for   their continued support.Grewal, et al.               Standards Track                   [Page 13]

RFC 5840               WESP for Traffic Visibility            April 20106.  References6.1.  Normative References   [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate                Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2410]    Glenn, R. and S. Kent, "The NULL Encryption Algorithm                and Its Use With IPsec",RFC 2410, November 1998.   [RFC3948]    Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and                M. Stenberg, "UDP Encapsulation of IPsec ESP Packets",RFC 3948, January 2005.   [RFC4303]    Kent, S., "IP Encapsulating Security Payload (ESP)",RFC4303, December 2005.   [RFC4543]    McGrew, D. and J. Viega, "The Use of Galois Message                Authentication Code (GMAC) in IPsec ESP and AH",RFC4543, May 2006.   [RFC5226]    Narten, T. and H. Alvestrand, "Guidelines for Writing an                IANA Considerations Section in RFCs",BCP 26,RFC 5226,                May 2008.6.2. Informative References   [RFC3947]    Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,                "Negotiation of NAT-Traversal in the IKE",RFC 3947,                January 2005.   [RFC4302]    Kent, S., "IP Authentication Header",RFC 4302, December                2005.   [RFC4306]    Kaufman, C., Ed., "Internet Key Exchange (IKEv2)                Protocol",RFC 4306, December 2005.   [Heuristics] Kivinen, T. and D. McDonald, "Heuristics for Detecting                ESP-NULL packets", Work in Progress, March 2010.Grewal, et al.               Standards Track                   [Page 14]

RFC 5840               WESP for Traffic Visibility            April 2010Authors' Addresses   Ken Grewal   Intel Corporation   2111 NE 25th Avenue, JF3-232   Hillsboro, OR  97124   USA   EMail: ken.grewal@intel.com   Gabriel Montenegro   Microsoft Corporation   One Microsoft Way   Redmond, WA  98052   USA   EMail: gabriel.montenegro@microsoft.com   Manav Bhatia   Alcatel-Lucent   Manyata Embassy   Nagawara Bangalore   India   EMail: manav.bhatia@alcatel-lucent.comGrewal, et al.               Standards Track                   [Page 15]

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