IPPM WG                                              K. Pentikousis, Ed.
Internet-Draft                                                      EICT
Intended status: Standards Track                                E. Zhang
Expires: August 15, November 30, 2015                                        Y. Cui
                                                     Huawei Technologies
                                                       February 11,
                                                            May 29, 2015


              IKEv2-derived Shared Secret Key for O/TWAMP


   The One-way Active Measurement Protocol (OWAMP) and Two-Way Active
   Measurement Protocol (TWAMP) security mechanism mechanisms require that both
   the client and server endpoints possess a shared secret.  Since the
   currently-standardized O/TWAMP security mechanism only supports a
   pre-shared key mode, large scale deployment of O/TWAMP is hindered
   significantly.  At the same time, recent trends point to wider
   Internet Key Exchange Protocol Version 2 (IKEv2) deployment which, in
   turn, calls for mechanisms and methods that enable tunnel end-users,
   as well as operators, to measure one-way and two- way network
   performance in a standardized manner.  This
   document describes the use of keys derived from an IKEv2 security
   association (SA) as the shared key in O/TWAMP.  If the shared key can
   be derived from the IKEv2 SA, O/TWAMP can support certificate-based
   key exchange, which would allow for more operational flexibility and
   efficiency.  The key derivation presented in this document can also
   facilitate automatic key management.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Scope and Applicability . . . . . . . . . . . . . . . . . . .   4
   4.  O/TWAMP Security  . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  O/TWAMP-Control Security  . . . . . . . . . . . . . . . .   5
     4.2.  O/TWAMP-Test Security . . . . . . . . . . . . . . . . . .   6
     4.3.  O/TWAMP Security Root . . . . . . . . . . . . . . . . . .   7
   5.  O/TWAMP for IPsec Networks  . . . . . . . . . . . . . . . . .   7
     5.1.  Shared Key Derivation . . . . . . . . . . . . . . . . . .   7
     5.2.  Server Greeting Message Update  . . . . . . . . . . . . .   8
     5.3.  Set-Up-Response Update  . . . . . . . . . . . . . . . . .  10   9
     5.4.  O/TWAMP over an IPsec tunnel  . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The One-way Active Measurement Protocol (OWAMP) [RFC4656] and the
   Two-Way Active Measurement Protocol (TWAMP) [RFC5357] can be used to
   measure network performance parameters such as latency, bandwidth,
   and packet loss by sending probe packets and monitoring their
   experience in the network.  In order to guarantee the accuracy of
   network measurement results, security aspects must be considered.
   Otherwise, attacks may occur and the authenticity of the measurement
   results may be violated.  For example, if no protection is provided,
   an adversary in the middle may modify packet timestamps, thus
   altering the measurement results.

   The currently-standardized O/TWAMP security mechanism [RFC4656]
   [RFC5357] requires that endpoints (i.e. both the client and the
   server) possess a shared secret.  In today's network deployments,
   however, the use of pre-shared keys is far from optimal.  For
   example, in wireless infrastructure networks, certain network
   elements, which can be seen as the two endpoints from an O/TWAMP
   perspective, support certificate-based security.  For instance,
   consider the case in which one wants to measure IP performance
   between a E-UTRAN Evolved Node B (eNB) and Security Gateway (SeGW).
   Both eNB and SeGW are 3GPP Long Term Evolution (LTE) nodes and
   support certificate mode and the Internet Key Exchange Protocol
   Version 2 (IKEv2).  Since the currently standardized

   The O/TWAMP security mechanism specified in [RFC4656] [RFC5357] only
   supports the pre-shared key mode, mode hindering large scale deployment of O/TWAMP is hindered significantly.
   O/TWAMP.  Furthermore, deployment and management of "shared secrets"
   for massive equipment installation consumes a tremendous amount of
   effort and is prone to human error.  At the same time, recent trends
   point to wider Internet Key Exchange Protocol Version 2 (IKEv2)
   deployment which, in turn, calls for mechanisms and methods that
   enable tunnel end-users, as well as operators, to measure one-way and
   two-way network performance in a standardized manner.

   With IKEv2 widely used, deployed, employing shared keys derived from IKEv2
   security association (SA) as shared key can be considered as a viable
   alternative.  In mobile telecommunication networks, the deployment
   rate of IPsec exceeds 95% with respect to alternative
   through the LTE serving network.
   In older-technology cellular networks, such as UMTS and GSM, IPsec
   use penetration is lower, but still quite significant. method described in this document.  If the shared key can
   be derived from the IKEv2 SA, O/TWAMP can support cert-based certificate-based
   key exchange and practically increase operational flexibility and
   efficiency.  The use of IKEv2 also makes it easier to extend
   automatic key management.

   In general, O/TWAMP measurement packets can be transmitted inside the
   IPsec tunnel, as it occurs with typical user traffic, or transmitted
   outside the IPsec tunnel.  This may depend on the operator's policy
   and the performance evaluation goal, and is orthogonal to the
   mechanism described in this document.  When IPsec is deployed,
   protecting O/TWAMP traffic in unauthenticated mode using IPsec is one
   option.  Another option is to protect O/TWAMP traffic using O/TWAMP the O/
   TWAMP layer security established using the PSK Pre-Shared Key (PSK)
   derived from IKEv2 but bypassing the IPsec tunnel.  Protecting
   unauthenticated O/TWAMP control and/or test traffic via
   Authentication Header (AH) [RFC4302] or Encapsulating Security
   Payload (ESP) [RFC4303]  cannot provide various security options,
   e.g. it cannot authenticate part of a O/TWAMP packet as mentioned in

   For measuring latency, a timestamp is carried in O/TWAMP test
   traffic.  The sender has to fetch the timestamp, encrypt it, and send
   it.  In  When the mechanism described in this case, document is used, partial
   authentication of O/TWAMP packets is possible and therefore the
   middle step can be skipped, potentially improving accuracy as the
   sequence number can be encrypted and authenticated before the
   timestamp is fetched.  It is the same case
   for the  The receiver since it can obtain obtains the timestamp by skipping without the
   need for the corresponding decryption step.  In such cases,
   protecting O/TWAMP traffic using O/
   TWAMP O/TWAMP layer security but bypassing
   the IPsec tunnel has its advantages.

   This document specifies a method for enabling network measurements
   between a TWAMP client and a TWAMP server, as discussed in Section 3.
   In short, the shared key used for securing TWAMP traffic is derived
   from IKEv2 [RFC7296].  From an operations and management perspective
   [RFC5706], the mechanism described in this document requires that
   both the TWAMP client Control-Client and server Server support IPsec.  This method
   IKEv2-derived keys SHOULD be used instead of shared secrets when O/TWAMP traffic is bypassing IPsec protection and O/
   TWAMP is
   running over an external network exactly between two IKEv2 systems. employed in a deployment using IKEv2.

   After clarifying the terminology and scope in the subsequent
   sections, the remainder of this document is organized as follows.
   Section 4 summarizes O/TWAMP protocol operation with respect to
   security.  Section 5 presents the method for binding TWAMP and IKEv2
   for network measurements between the client and the server which both
   support IKEv2.  Finally, Section 6 discusses the security
   considerations arising from the proposed mechanisms.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Scope and Applicability

   This document reserves from the TWAMP-Modes registry

   TWAMP implementations signal the Mode value use of this method by setting
   IKEv2Derived which is equal to 128 (i.e. bit set in position (see Section 7) and
   MUST be used by TWAMP implementations compatible with this

   Although the control procedures described in this document are
   applicable to OWAMP per se, the lack of an established IANA registry
   for OWAMP Mode values akin to that listed in Section 7 technically
   prevents us from extending OWAMP Mode values.  Therefore, independent
   OWAMP implementations SHOULD be checked for full compatibility with
   respect to the use of this Mode value.  Until an IANA registry for
   OWAMP Mode values is established, the use of this feature in OWAMP
   implementations MUST be arranged privately among consenting OWAMP

4.  O/TWAMP Security

   Security for O/TWAMP-Control and O/TWAMP-Test are briefly reviewed in
   the following subsections.

4.1.  O/TWAMP-Control Security

   O/TWAMP uses a simple cryptographic protocol which relies on

   o  AES  Advanced Encryption Standard (AES) in Cipher Block Chaining (AES-CBC) (AES-
      CBC) for confidentiality

   o  HMAC-SHA1  Hash-based Message Authentication Code (HMAC)-Secure Hash
      Algorithm1 (SHA1) truncated to 128 bits for message authentication

   Three modes of operation are supported in the OWAMP-Control protocol:
   unauthenticated, authenticated, and encrypted.  In addition to these
   modes, the TWAMP-Control protocol also supports a mixed mode, i.e.
   the TWAMP-Control protocol operates in encrypted mode while TWAMP-
   Test protocol operates in unauthenticated mode.  The authenticated,
   encrypted and mixed modes require that endpoints possess a shared
   secret, typically a passphrase.  The secret key is derived from the
   passphrase using a password-based key derivation function PBKDF2
   (PKCS#5) [RFC2898].

   In the unauthenticated mode, the security parameters are left unused.
   In the authenticated, encrypted and mixed modes, the security
   parameters are negotiated during the control connection

   Figure 1 illustrates the initiation stage of the O/TWAMP-Control
   protocol between a client Control-Client and the server. a Server.  In short, the client
   Control-Client opens a TCP connection to the server Server in order to be
   able to send O/TWAMP-
   Control O/TWAMP-Control commands.  The server Server responds with a
   Server Greeting, which contains the Modes, Challenge, Salt, Count,
   and MBZ fields (see Section 3.1 of [RFC4656]).  If the client-preferred Control-Client
   preferred mode is available, the client responds with a Set-Up-
   Response message, wherein the selected Mode, as well as the KeyID,
   Token and Client initialization vector (IV) are included.  The Token
   is the concatenation of a 16-octet Challenge, a 16-octet AES Session-key Session-
   key used for encryption, and a 32-octet HMAC-SHA1 Session-key used
   for authentication.  The Token is encrypted using AES-CBC.


   +----------------+                  +--------+
   | Client Control-Client |                  | Server |
   +----------------+                  +--------+
            |                               |
            |<------ TCP Connection Connection-- ----->|
            |                               |
            |<------ Greeting message ----| ------|
            |                               |
            |------- Set-Up-Response ---->| ------>|
            |                               |
            |<------ Server-Start --------| ----------|
            |                               |

                  Figure 1: Initiation of O/TWAMP-Control

   Encryption uses a key derived from the shared secret associated with
   KeyID.  In the authenticated, encrypted and mixed modes, all further
   communication is encrypted using the AES Session-key and
   authenticated with the HMAC Session-key.  After receiving the Set-Up-
   Response the server Server responds with a Server-Start message containing
   the Server-IV.  The client Control-Client encrypts everything it transmits
   through the just-established O/TWAMP-Control connection using stream
   encryption with Client- IV as the IV.  Correspondingly, the server Server
   encrypts its side of the connection using Server-IV as the IV.  The
   IVs themselves are transmitted in cleartext.  Encryption starts with
   the block immediately following that containing the IV.

   The AES Session-key and HMAC Session-key are generated randomly by
   the client. Control-Client.  The HMAC Session-key is communicated along with
   the AES Session-key during O/TWAMP-Control connection setup.  The
   HMAC Session-key is derived independently of the AES Session-key.

4.2.  O/TWAMP-Test Security

   The O/TWAMP-Test protocol runs over UDP, using the client Session-Sender and server
   Session-Reflector IP and port numbers that were negotiated during the
   Request-Session exchange.  O/TWAMP- Test has the same mode with O/TWAMP-Control O/
   TWAMP-Control and all O/TWAMP-Test sessions inherit the corresponding
   O/TWAMP-Control session mode except when operating in mixed mode.

   The O/TWAMP-Test packet format is the same in authenticated and
   encrypted modes.  The encryption and authentication operations are,
   however, different.  Similarly with the respective O/TWAMP-Control
   session, each O/TWAMP-Test session has two keys: an AES Session-key
   and an HMAC Session-key.  However, there is a difference in how the
   keys are obtained:

   O/TWAMP-Control:  the keys are generated by the client Control-Client and
           communicated to the server Server during the control connection
           establishment with the Set-Up-Response message (as part of
           the Token).

   O/TWAMP-Test:  the keys are derived from the O/TWAMP-Control keys and
           the session identifier (SID), which serve as inputs of the
           key derivation function (KDF).  The O/TWAMP-Test AES Session-
           key is generated using the O/TWAMP- Control AES Session-key,
           with the 16-octet session identifier (SID), for encrypting
           and decrypting the packets of the particular O/TWAMP-Test
           session.  The O/TWAMP-Test HMAC Session-key is generated
           using the O/TWAMP-Control HMAC Session-key, with the 16-octet
           session identifier (SID), for authenticating the packets of
           the particular O/TWAMP-Test session.

4.3.  O/TWAMP Security Root

   As discussed above, the AES Session-key and HMAC Session-key used by
   the O/TWAMP-Test protocol are derived from the AES Session-key and
   HMAC Session-key which are used in the O/TWAMP-Control protocol.  The
   AES Session-key and HMAC Session-key used in the O/TWAMP-Control
   protocol are generated randomly by the client, Control-Client, and encrypted
   with the shared secret associated with KeyID.  Therefore, the
   security root is the shared secret key.  Thus, for large deployments,
   key provision and management may become overly complicated.
   Comparatively, a certificate-based approach using IKEv2 can
   automatically manage the security root and solve this problem, as we
   explain in Section 5.

5.  O/TWAMP for IPsec Networks

   This section presents a method of binding O/TWAMP and IKEv2 for
   network measurements between a client and a server which both support
   IPsec.  In short, the shared key used for securing O/TWAMP traffic is
   derived using IKEv2 [RFC7296].

5.1.  Shared Key Derivation

   In the authenticated, encrypted and mixed modes, the shared secret
   key MUST be derived from the IKEv2 Security Association (SA).  Note
   that we explicitly opt to derive the shared secret key from the IKEv2
   SA, rather than the child SA, since the use case whereby an IKEv2 SA
   can be created without generating any child SA is possible [RFC6023].

   When the shared secret key is derived from the IKEv2 SA, SK_d must be
   generated first.  SK_d MUST must be computed as per [RFC7296].

   The shared secret key MUST be generated as follows:

      Shared secret key = prf( SK_d, "IPPM" )

   Wherein the string "IPPM" comprises four is encoded in ASCII characters and "prf" is a
   pseudorandom function.

   It is recommended that the shared secret key is derived in the IPsec layer.  This way, the
   layer so that IPsec keying material is not exposed to the O/TWAMP
   client.  Note, however, that the interaction between the O/TWAMP and
   IPsec layers is host-internal and implementation-specific.
   Therefore, this is clearly outside the scope of this document, which
   focuses on the interaction between the O/TWAMP client and server.
   That said, one possible way could be the following: at the client Control-
   Client side, the IPSec layer can perform a lookup in the Security
   Association Database (SAD) using the IP address of the server Server and
   thus match the corresponding IKEv2 SA.  At the server Server side, the IPSec
   layer can look up the corresponding IKEv2 SA by using the SPIs Security
   Parameter Indexes (SPIs) sent by the client, Control-Client (see
   Section 5.3), and therefore extract the shared secret key.

   In case that both client and server do support IKEv2 but there is no
   current IKEv2 SA, two alternative ways could be considered.  First,
   the O/TWAMP client Control-Client initiates the establishment of the IKEv2
   SA, logs this operation, and selects the mode which supports IKEv2.
   Alternatively, the O/TWAMP client Control-Client does not initiate the
   establishment of the IKEv2 SA, logs an error for operational
   management purposes, and proceeds with the modes defined in
   [RFC4656][RFC5357][RFC5618].  Again, although both alternatives are
   feasible, they are in fact implementation-specific.

   If rekeying for the IKEv2 SA or deletion of the IKEv2 SA occurs, the
   corresponding shared secret key generated from the SA can MUST continue
   to be used until the O/TWAMP session terminates.

5.2.  Server Greeting Message Update

   To achieve trigger a binding association between the key generated from IKEv2
   and the O/TWAMP shared secret key, the Modes field in the Server
   Greeting Message should
   include these extensions, (Figure 2) will need to allow for support of key
   derivation as discussed in Figure 2. Section 5.1.  Therefore, when this method
   is used, the Modes value extension MUST be supported.  Support for
   deriving the shared key from the IKEv2 SA is indicated by setting
   IKEv2Derived (see Section 7).

   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
   |                                                               |
   |                       Unused (12 octets)                      |
   |                                                               |
   |                           Modes                               |
   |                                                               |
   |                     Challenge (16 octets)                     |
   |                                                               |
   |                                                               |
   |                                                               |
   |                        Salt (16 octets)                       |
   |                                                               |
   |                                                               |
   |                        Count (4 octets)                       |
   |                                                               |
   |                        MBZ (12 octets)                        |
   |                                                               |

                     Figure 2: Server Greeting format

   The Modes field in Figure 2 will need to allow for support of key
   derivation as discussed in Section 5.1.  As such, the Modes value
   extension MUST be supported by implementations compatible with this
   document, indicating support for deriving the shared key from the
   IKEv2 SA.  The new Modes value indicating support for this
   specification is IKEv2Derived and is equal to 128 (i.e. bit set in
   position 7).  Clearly, an implementation compatible with this
   specification MUST support the authenticated, encrypted and mixed
   modes as per [RFC4656][RFC5357][RFC5618].

   The choice of this set of Modes values poses no backwards
   compatibility problems to existing O/TWAMP clients.  Robust legacy
   Control-Client implementations would disregard the fact that the
   IKEv2Derived Modes bit in the Server Greeting is set.  On the other
   hand, a client
   compatible with Control-Client implementing this specification method can easily identify that the O/
   TWAMP server
   O/TWAMP Server contacted does not support this specification.  If the
   Server supports other Modes, as one could assume, the client Control-Client
   would then decide which Mode to use and indicate such accordingly as
   per [RFC4656][RFC5357].  A client compatible with Control-Client implementing this specification method
   which decides not to employ IKEv2 derivation, can simply behave as a
   purely [RFC4656]/[RFC5357] compatible client.

5.3.  Set-Up-Response Update

   The Set-Up-Response Message should be Figure 3 is updated as in Figure 3. follows.  When a
   O/TWAMP client compatible with Control-Client implementing this specification method receives a Server
   Greeting indicating support for Mode IKEv2Derived it SHOULD reply to
   the O/TWAMP server Server with a Set-Up response that indicates so.  For
   example, a compatible O/TWAMP client Control-Client choosing the
   authenticated mode with IKEv2 shared secret key derivation should set
   Mode to 130, i.e. set the bits in positions 1 and 7 to one. one (see
   Section 7).

   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
   |                            Mode                               |
   |                                                               |
   |                     Key ID (80 octets)                        |
   |                                                               |
   |                                                               |
   |                                                               |
   |                     Token (16 octets)                         |
   |                                                               |
   |                                                               |
   |                                                               |
   |                    Client-IV (12 octets)                      |
   |                                                               |

                     Figure 3: Set-Up-Response Message

   The Security Parameter Index (SPI)(see [RFC4301] [RFC7296]) can uniquely identify
   identifies the Security Association (SA).  If the client Control-Client
   supports the derivation of shared secret key from IKEv2 SA, it will
   choose the corresponding mode value and carry SPIi and SPIr in the
   Key ID field.  SPIi and SPIr MUST be included in the Key ID field of
   the Set-Up-Response Message to indicate the IKEv2 SA from which the O/
   O/TWAMP shared secret key derived from.  The length of SPI is 8
   octets.  Therefore, the first 8 octets of Key ID field MUST carry
   SPIi and the second 8 octets MUST carry SPIr.  The remaining bits of
   the Key ID field MUST be set to zero.

   A O/TWAMP server which supports the specification Server implementation of this document, method, MUST obtain the SPIi
   and SPIr from the first 16 octets and ignore the remaining octets of
   the Key ID field.  Then, the client Control-Client and the
   server Server can derive
   the shared secret key based on the mode Mode value and SPI.  If the O/TWAMP server O/
   TWAMP Server cannot find the IKEv2 SA corresponding to the SPIi and
   SPIr received, it MUST log the event for operational management
   purposes.  In addition, the O/TWAMP server Server SHOULD set the Accept
   field of the Server-Start message to the value 6 to indicate that server the
   Server is not willing to conduct further transactions in this O/
   TWAMP-Control session since it can not find the corresponding IKEv2

5.4.  O/TWAMP over an IPsec tunnel

   IPsec Authentication Header (AH) [RFC4302] and Encapsulating Security
   Payload (ESP) [RFC4303] provide confidentiality and data integrity to
   IP datagrams.  An IPsec tunnel can be used to provide the protection
   needed for O/TWAMP Control and Test packets, even if the peers choose
   the unauthenticated mode of operation.  In order to ensure
   authenticity and security, the IPsec tunnel O/TWAMP packets between two IKEv2 systems
   SHOULD be configured to
   include O/TWAMP measurement packets use the corresponding IPsec tunnel running
   over an external network even when using the O/TWAMP unauthenticated

6.  Security Considerations

   As the shared secret key is derived from the IKEv2 SA, the key
   derivation algorithm strength and limitations are as per [RFC7296].
   The strength of a key derived from a Diffie-Hellman exchange using
   any of the groups defined here depends on the inherent strength of
   the group, the size of the exponent used, and the entropy provided by
   the random number generator employed.  The strength of all keys and
   implementation vulnerabilities, particularly Denial of Service (DoS)
   attacks are as defined in [RFC7296].

7.  IANA Considerations

   IANA is requested to allocate

   During the IKEv2Derived Mode bit production of this document, the authors and reviewers
   noticed that the TWAMP-Modes registry, which should describe a
   bitfield of flags, instead is equal defined as a registry of integer
   values.  In addition, the Semantics Definition column seems to 128 (i.e. bit set in position 7) have
   spurious information in the TWAMP-Modes registry. it.  The
   TWAMP-Modes registry should be augmented changed to
   correct these issues, as follows:

   Value  Description             Semantics Definition
   128    IKEv2 Derived           This memo,

 Bit|Description                                |Semantics   |Reference|
    |                                           |Definition  |         |
 0   Unauthenticated                             Section 5.2
          Mode 3.1  [RFC4656]
 1   Authenticated                               Section 3.1  [RFC4656]
 2   Encrypted                                   Section 3.1  [RFC4656]
 3   Unauth.TEST protocol,Encrypted CONTROL      Section 3.1  [RFC5618]
 4   Individual Session Control                               [RFC5938]
 5   Reflect Octets Capability                                [RFC6038]
 6   Symmetrical Size Sender Test Packet Format               [RFC6038]

                      Figure 4: TWAMP Modes registry

   In addition, this document adds a new bit position entry to this registry:

 Bit|Description                                |Semantics   |Reference|
    |                                           |Definition  |         |
 7   IKEv2Derived Mode Capability                Section 5    [RFCxxxx]

 (where RFCxxxx refers to draft-ietf-ippm-ipsec).

                  Figure 4: 5: IKEv2 Modes Derived Mode Capability

8.  Acknowledgments

   We thank Eric Chen, Yaakov Stein, Brian Trammell, Emily Bi, John
   Mattsson, Steve Baillargeon, Spencer Dawkins, Tero Kivinen, Fred
   Baker, Meral Shirazipour, and Hannes Tschofenig Tschofenig, Ben Campbell, Stephen
   Farrell, Brian Haberman, and Barry Leiba for their reviews, comments
   and text suggestions.

   Al Morton deserves a special mention for his thorough reviews and
   text contributions to this document as well as the constructive
   discussions over several IPPM meetings.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302, December

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
              4303, December 2005.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
              Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
              August 2009.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, October 2014.

9.2.  Informative References

   [RFC2898]  Kaliski, B., "PKCS #5: Password-Based Cryptography
              Specification Version 2.0", RFC 2898, September 2000.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions", RFC
              5706, November 2009.

   [RFC6023]  Nir, Y., Tschofenig, H., Deng, H., and R. Singh, "A
              Childless Initiation of the Internet Key Exchange Version
              2 (IKEv2) Security Association (SA)", RFC 6023, October

Authors' Addresses

   Kostas Pentikousis (editor)
   EICT GmbH
   EUREF-Campus Haus 13
   Torgauer Strasse 12-15
   10829 Berlin

   Email: k.pentikousis@eict.de

   Emma Zhang
   Huawei Technologies
   Huawei Building, No.3, Rd. XinXi
   Haidian District , Beijing   100095
   P. R. China

   Email: emma.zhanglijia@huawei.com
   Yang Cui
   Huawei Technologies
   Otemachi First Square 1-5-1 Otemachi
   Chiyoda-ku, Tokyo   100-0004

   Email: cuiyang@huawei.com