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RFC 8231

 
 
 

Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE

Part 4 of 4, p. 42 to 57
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8.  IANA Considerations

   The code points described below have been allocated for the protocol
   elements defined in this document.

8.1.  PCE Capabilities in IGP Advertisements

   The following bits have been registered in the "Path Computation
   Element (PCE) Capability Flags" subregistry of the "Open Shortest
   Path First (OSPF) Parameters" registry:

           Bit   Description                        Reference
           ---   -------------------------------    -------------
            11   Active stateful PCE capability     This document
            12   Passive stateful PCE capability    This document

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8.2.  PCEP Messages

   The following message types have been allocated within the "PCEP
   Messages" subregistry of the "Path Computation Element Protocol
   (PCEP) Numbers" registry:

                    Value  Description    Reference
                    -----  ------------   -------------
                      10   Report         This document
                      11   Update         This document

8.3.  PCEP Objects

   The following object-class values and object types have been
   allocated within the "PCEP Objects" subregistry of the "Path
   Computation Element Protocol (PCEP) Numbers" registry:

          Object-Class Value  Name                  Reference
          ------------------  ----------------      -------------
                  32          LSP                   This document
                              Object-Type
                              0: Reserved
                              1: LSP

                  33          SRP                   This document
                              Object-Type
                              0: Reserved
                              1: SRP

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8.4.  LSP Object

   A new subregistry, named "LSP Object Flag Field", has been created
   within the "Path Computation Element Protocol (PCEP) Numbers"
   registry to manage the Flag field of the LSP object.  New values are
   assigned by Standards Action [RFC8126].  Each bit should be tracked
   with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   The following values are defined in this document:

                 Bit     Description           Reference
                 ---     --------------------  -------------
                 0-4     Unassigned            This document
                 5-7     Operational (3 bits)  This document
                  8      Administrative        This document
                  9      Remove                This document
                  10     SYNC                  This document
                  11     Delegate              This document

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8.5.  PCEP-Error Object

   The following error types and error values have been registered
   within the "PCEP-ERROR Object Error Types and Values" subregistry of
   the "Path Computation Element Protocol (PCEP) Numbers" registry:


   Error-Type  Meaning
   ----------  -------------------------------------------------------
      6        Mandatory Object missing

                Error-value
                8:   LSP object missing
                9:   ERO object missing
                10:  SRP object missing
                11:  LSP-IDENTIFIERS TLV missing

      19       Invalid Operation

                Error-value
                1:   Attempted LSP Update Request for a non-delegated
                     LSP.  The PCEP-ERROR object is followed by the LSP
                     object that identifies the LSP.
                2:   Attempted LSP Update Request if the stateful PCE
                     capability was not advertised.
                3:   Attempted LSP Update Request for an LSP identified
                     by an unknown PLSP-ID.
                5:   Attempted LSP State Report if stateful PCE
                     capability was not advertised.

      20       LSP State Synchronization Error

                Error-value
                1:   A PCE indicates to a PCC that it cannot process (an
                     otherwise valid) LSP State Report.  The PCEP-ERROR
                     object is followed by the LSP object that
                     identifies the LSP.
                5:   A PCC indicates to a PCE that it cannot complete
                     the State Synchronization.

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8.6.  Notification Object

   The following Notification Types and Notification Values have been
   allocated within the "Notification Object" subregistry of the "Path
   Computation Element Protocol (PCEP) Numbers" registry:


   Notification-Type  Name
   4     Stateful PCE resource limit exceeded

             Notification-value
             1:   Entering resource limit exceeded state
             2:   Deprecated

   Note that the early allocation included an additional Notification
   Value 2 for "Exiting resource limit exceeded state".  This
   Notification Value is no longer required and has been marked as
   "Deprecated".

8.7.  PCEP TLV Type Indicators

   The following TLV Type Indicator values have been registered within
   the "PCEP TLV Type Indicators" subregistry of the "Path Computation
   Element Protocol (PCEP) Numbers" registry:

              Value     Description                 Reference
              -----     -----------------------     -------------
                16      STATEFUL-PCE-CAPABILITY     This document
                17      SYMBOLIC-PATH-NAME          This document
                18      IPV4-LSP-IDENTIFIERS        This document
                19      IPV6-LSP-IDENTIFIERS        This document
                20      LSP-ERROR-CODE              This document
                21      RSVP-ERROR-SPEC             This document

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8.8.  STATEFUL-PCE-CAPABILITY TLV

   A new subregistry, named "STATEFUL-PCE-CAPABILITY TLV Flag Field",
   has been created within the "Path Computation Element Protocol (PCEP)
   Numbers" registry to manage the Flag field in the STATEFUL-PCE-
   CAPABILITY TLV of the PCEP OPEN object (class = 1).  New values are
   assigned by Standards Action [RFC8126].  Each bit should be tracked
   with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   The following values are defined in this document:

               Value  Description              Reference
               -----  ---------------------    -------------
                 31   LSP-UPDATE-CAPABILITY    This document

8.9.  LSP-ERROR-CODE TLV

   A new subregistry, named "LSP-ERROR-CODE TLV Error Code Field", has
   been created within the "Path Computation Element Protocol (PCEP)
   Numbers" registry to manage the LSP Error Code field of the LSP-
   ERROR-CODE TLV.  This field specifies the reason for failure to
   update the LSP.

   New values are assigned by Standards Action [RFC8126].  Each value
   should be tracked with the following qualities: value, meaning, and
   defining RFC.  The following values are defined in this document:

               Value      Meaning
                ---       -------------------------------------
                 0        Reserved
                 1        Unknown reason
                 2        Limit reached for PCE-controlled LSPs
                 3        Too many pending LSP Update Requests
                 4        Unacceptable parameters
                 5        Internal error
                 6        LSP administratively brought down
                 7        LSP preempted
                 8        RSVP signaling error

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9.  Manageability Considerations

   All manageability requirements and considerations listed in [RFC5440]
   apply to the PCEP extensions defined in this document.  In addition,
   requirements and considerations listed in this section apply.

9.1.  Control Function and Policy

   In addition to configuring specific PCEP session parameters, as
   specified in [RFC5440], Section 8.1, a PCE or PCC implementation MUST
   allow configuring the stateful PCEP capability and the LSP Update
   capability.  A PCC implementation SHOULD allow the operator to
   specify multiple candidate PCEs for and a delegation preference for
   each candidate PCE.  A PCC SHOULD allow the operator to specify an
   LSP delegation policy where LSPs are delegated to the most-preferred
   online PCE.  A PCC MAY allow the operator to specify different LSP
   delegation policies.

   A PCC implementation that allows concurrent connections to multiple
   PCEs SHOULD allow the operator to group the PCEs by administrative
   domains, and it MUST NOT advertise LSP existence and state to a PCE
   if the LSP is delegated to a PCE in a different group.

   A PCC implementation SHOULD allow the operator to specify whether the
   PCC will advertise LSP existence and state for LSPs that are not
   controlled by any PCE (for example, LSPs that are statically
   configured at the PCC).

   A PCC implementation SHOULD allow the operator to specify both the
   Redelegation Timeout Interval and the State Timeout Interval.  The
   default value of the Redelegation Timeout Interval SHOULD be set to
   30 seconds.  An operator MAY also configure a policy that will
   dynamically adjust the Redelegation Timeout Interval, for example
   setting it to zero when the PCC has an established session to a
   backup PCE.  The default value for the State Timeout Interval SHOULD
   be set to 60 seconds.

   After the expiration of the State Timeout Interval, the LSP reverts
   to operator-defined default parameters.  A PCC implementation MUST
   allow the operator to specify the default LSP parameters.  To achieve
   a behavior where the LSP retains the parameters set by the PCE until
   such time that the PCC makes a change to them, a State Timeout
   Interval of infinity SHOULD be used.  Any changes to LSP parameters
   SHOULD be done in a make-before-break fashion.

   LSP delegation is controlled by operator-defined policies on a PCC.
   LSPs are delegated individually -- different LSPs may be delegated to
   different PCEs.  An LSP is delegated to at most one PCE at any given

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   point in time.  A PCC implementation SHOULD support the delegation
   policy, when all PCC's LSPs are delegated to a single PCE at any
   given time.  Conversely, the policy revoking the delegation for all
   PCC's LSPs SHOULD also be supported.

   A PCC implementation SHOULD allow the operator to specify delegation
   priority for PCEs.  This effectively defines the primary PCE and one
   or more backup PCEs to which a primary PCE's LSPs can be delegated
   when the primary PCE fails.

   Policies defined for stateful PCEs and PCCs should eventually fit in
   the policy-enabled path computation framework defined in [RFC5394],
   and the framework should be extended to support stateful PCEs.

9.2.  Information and Data Models

   The PCEP YANG module [PCEP-YANG] should include:

   o  advertised stateful capabilities and synchronization status per
      PCEP session.

   o  the delegation status of each configured LSP.

   The PCEP MIB [RFC7420] could also be updated to include this
   information.

9.3.  Liveness Detection and Monitoring

   PCEP extensions defined in this document do not require any new
   mechanisms beyond those already defined in [RFC5440], Section 8.3.

9.4.  Verifying Correct Operation

   Mechanisms defined in [RFC5440], Section 8.4 also apply to PCEP
   extensions defined in this document.  In addition to monitoring
   parameters defined in [RFC5440], a stateful PCC-side PCEP
   implementation SHOULD provide the following parameters:

   o  Total number of LSP Updates

   o  Number of successful LSP Updates

   o  Number of dropped LSP Updates

   o  Number of LSP Updates where LSP setup failed

   A PCC implementation SHOULD provide a command to show for each LSP
   whether it is delegated, and if so, to which PCE.

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   A PCC implementation SHOULD allow the operator to manually revoke LSP
   delegation.

9.5.  Requirements on Other Protocols and Functional Components

   PCEP extensions defined in this document do not put new requirements
   on other protocols.

9.6.  Impact on Network Operation

   Mechanisms defined in [RFC5440], Section 8.6 also apply to PCEP
   extensions defined in this document.

   Additionally, a PCEP implementation SHOULD allow a limit to be placed
   on the number of LSPs delegated to the PCE and on the rate of PCUpd
   and PCRpt messages sent by a PCEP speaker and processed from a peer.
   It SHOULD also allow sending a notification when a rate threshold is
   reached.

   A PCC implementation SHOULD allow a limit to be placed on the rate of
   LSP Updates to the same LSP to avoid signaling overload discussed in
   Section 10.3.

10.  Security Considerations

10.1.  Vulnerability

   This document defines extensions to PCEP to enable stateful PCEs.
   The nature of these extensions and the delegation of path control to
   PCEs results in more information being available for a hypothetical
   adversary and a number of additional attack surfaces that must be
   protected.

   The security provisions described in [RFC5440] remain applicable to
   these extensions.  However, because the protocol modifications
   outlined in this document allow the PCE to control path computation
   timing and sequence, the PCE defense mechanisms described in
   [RFC5440], Section 7.2 are also now applicable to PCC security.

   As a general precaution, it is RECOMMENDED that these PCEP extensions
   only be activated on authenticated and encrypted sessions across PCEs
   and PCCs belonging to the same administrative authority, using
   Transport Layer Security (TLS) [PCEPS], as per the recommendations
   and best current practices in [RFC7525].

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   The following sections identify specific security concerns that may
   result from the PCEP extensions outlined in this document along with
   recommended mechanisms to protect PCEP infrastructure against related
   attacks.

10.2.  LSP State Snooping

   The stateful nature of this extension explicitly requires LSP status
   updates to be sent from PCC to PCE.  While this gives the PCE the
   ability to provide more optimal computations to the PCC, it also
   provides an adversary with the opportunity to eavesdrop on decisions
   made by network systems external to PCE.  This is especially true if
   the PCC delegates LSPs to multiple PCEs simultaneously.

   Adversaries may gain access to this information by eavesdropping on
   unsecured PCEP sessions and might then use this information in
   various ways to target or optimize attacks on network infrastructure,
   for example, by flexibly countering anti-DDoS measures being taken to
   protect the network or by determining choke points in the network
   where the greatest harm might be caused.

   PCC implementations that allow concurrent connections to multiple
   PCEs SHOULD allow the operator to group the PCEs by administrative
   domains, and they MUST NOT advertise LSP existence and state to a PCE
   if the LSP is delegated to a PCE in a different group.

10.3.  Malicious PCE

   The LSP delegation mechanism described in this document allows a PCC
   to grant effective control of an LSP to the PCE for the duration of a
   PCEP session.  While this enables PCE control of the timing and
   sequence of path computations within and across PCEP sessions, it
   also introduces a new attack vector: an attacker may flood the PCC
   with PCUpd messages at a rate that exceeds either the PCC's ability
   to process them or the network's ability to signal the changes, by
   either spoofing messages or compromising the PCE itself.

   A PCC is free to revoke an LSP delegation at any time without needing
   any justification.  A defending PCC can do this by enqueueing the
   appropriate PCRpt message.  As soon as that message is enqueued in
   the session, the PCC is free to drop any incoming PCUpd messages
   without additional processing.

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10.4.  Malicious PCC

   A stateful session also results in an increased attack surface by
   placing a requirement for the PCE to keep an LSP state replica for
   each PCC.  It is RECOMMENDED that PCE implementations provide a limit
   on resources a single PCC can occupy.  A PCE implementing such a
   limit MUST send a PCNtf message with notification-type 4 (Stateful
   PCE resource limit exceeded) and notification-value 1 (Entering
   resource limit exceeded state) upon receiving an LSP State Report
   causing it to exceed this threshold.

   Delegation of LSPs can create further strain on PCE resources and a
   PCE implementation MAY preemptively give back delegations if it finds
   itself lacking the resources needed to effectively manage the
   delegation.  Since the delegation state is ultimately controlled by
   the PCC, PCE implementations SHOULD provide throttling mechanisms to
   prevent strain created by flaps of either a PCEP session or an LSP
   delegation.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <https://www.rfc-editor.org/info/rfc5088>.

   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
              January 2008, <https://www.rfc-editor.org/info/rfc5089>.

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   [RFC5284]  Swallow, G. and A. Farrel, "User-Defined Errors for RSVP",
              RFC 5284, DOI 10.17487/RFC5284, August 2008,
              <https://www.rfc-editor.org/info/rfc5284>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, DOI 10.17487/RFC5511, April
              2009, <https://www.rfc-editor.org/info/rfc5511>.

   [RFC8051]  Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,
              <https://www.rfc-editor.org/info/rfc8051>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

   [MPLS-PC]  Chaieb, I., Le Roux, JL., and B. Cousin, "Improved MPLS-TE
              LSP Path Computation using Preemption", Global
              Information Infrastructure Symposium,
              DOI 10.1109/GIIS.2007.4404195, July 2007.

   [MXMN-TE]  Danna, E., Mandal, S., and A. Singh, "A practical
              algorithm for balancing the max-min fairness and
              throughput objectives in traffic engineering", INFOCOM,
              2012 Proceedings IEEE, pp. 846-854,
              DOI 10.1109/INFCOM.2012.6195833, March 2012.

   [PCE-Init-LSP]
              Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
              Extensions for PCE-initiated LSP Setup in a Stateful PCE
              Model", Work in Progress,
              draft-ietf-pce-pce-initiated-lsp-10, June 2017.

   [PCEP-GMPLS]
              Margaria, C., de Dios, O., and F. Zhang, "PCEP extensions
              for GMPLS", Work in Progress,
              draft-ietf-pce-gmpls-pcep-extensions-11, October 2015.

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   [PCEP-YANG]
              Dhody, D., Hardwick, J., Beeram, V., and j.
              jefftant@gmail.com, "A YANG Data Model for Path
              Computation Element Communications Protocol (PCEP)", Work
              in Progress, draft-ietf-pce-pcep-yang-05, June 2017.

   [PCEPS]    Lopez, D., de Dios, O., Wu, Q., and D. Dhody, "Secure
              Transport for PCEP", Work in Progress,
              draft-ietf-pce-pceps-18, September 2017.

   [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
              McManus, "Requirements for Traffic Engineering Over MPLS",
              RFC 2702, DOI 10.17487/RFC2702, September 1999,
              <https://www.rfc-editor.org/info/rfc2702>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC3346]  Boyle, J., Gill, V., Hannan, A., Cooper, D., Awduche, D.,
              Christian, B., and W. Lai, "Applicability Statement for
              Traffic Engineering with MPLS", RFC 3346,
              DOI 10.17487/RFC3346, August 2002,
              <https://www.rfc-editor.org/info/rfc3346>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

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   [RFC5394]  Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
              "Policy-Enabled Path Computation Framework", RFC 5394,
              DOI 10.17487/RFC5394, December 2008,
              <https://www.rfc-editor.org/info/rfc5394>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
              and D. Dhody, "Optimizations of Label Switched Path State
              Synchronization Procedures for a Stateful PCE", RFC 8232,
              DOI 10.17487/RFC8232, September 2017,
              <http://www.rfc-editor.org/info/rfc8232>.

Acknowledgements

   We would like to thank Adrian Farrel, Cyril Margaria, and Ramon
   Casellas for their contributions to this document.

   We would like to thank Shane Amante, Julien Meuric, Kohei Shiomoto,
   Paul Schultz, and Raveendra Torvi for their comments and suggestions.
   Thanks also to Jon Hardwick, Oscar Gonzales de Dios, Tomas Janciga,
   Stefan Kobza, Kexin Tang, Matej Spanik, Jon Parker, Marek Zavodsky,
   Ambrose Kwong, Ashwin Sampath, Calvin Ying, Mustapha Aissaoui,
   Stephane Litkowski, and Olivier Dugeon for helpful comments and
   discussions.

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Contributors

   The following people contributed substantially to the content of this
   document and should be considered coauthors:

   Xian Zhang
   Huawei Technology
   F3-5-B R&D Center
   Huawei Industrial Base, Bantian, Longgang District
   Shenzhen, Guangdong 518129
   China
   Email: zhang.xian@huawei.com

   Dhruv Dhody
   Huawei Technology
   Leela Palace
   Bangalore, Karnataka 560008
   INDIA
   Email: dhruv.dhody@huawei.com

   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario K2K 3E8
   Canada
   Email: msiva@cisco.com

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Authors' Addresses

   Edward Crabbe
   Oracle
   1501 4th Ave, suite 1800
   Seattle, WA  98101
   United States of America

   Email: edward.crabbe@oracle.com


   Ina Minei
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   United States of America

   Email: inaminei@google.com


   Jan Medved
   Cisco Systems, Inc.
   170 West Tasman Dr.
   San Jose, CA  95134
   United States of America

   Email: jmedved@cisco.com


   Robert Varga
   Pantheon Technologies SRO
   Mlynske Nivy 56
   Bratislava  821 05
   Slovakia

   Email: robert.varga@pantheon.tech