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SPRING Working Group                                           G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                             J. Tantsura
Expires: February 24, 2019                                Nuage Networks
                                                           I. Varlashkin
                                                                  Google
                                                                 M. Chen
                                                                  Huawei
                                                         August 23, 2018


  Bidirectional Forwarding Detection (BFD) in Segment Routing Networks
                          Using MPLS Dataplane
                       draft-mirsky-spring-bfd-06

Abstract

   Segment Routing (SR) architecture leverages the paradigm of source
   routing.  It can be realized in the Multiprotocol Label Switching
   (MPLS) network without any change to the data plane.  A segment is
   encoded as an MPLS label, and an ordered list of segments is encoded
   as a stack of labels.  Bidirectional Forwarding Detection (BFD) is
   expected to monitor any existing path between systems.  This document
   defines how to use Label Switched Path Ping to bootstrap a BFD
   session, control path in reverse direction of the SR-MPLS tunnel and
   applicability of BFD Demand mode in the SR-MPLS domain.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 24, 2019.








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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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
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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Bootstrapping BFD Session over Segment Routed Tunnel with
       MPLS Data Plane . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Use BFD Reverse Path TLV over Segment Routed MPLS Tunnel  . .   5
   4.  Use Non-FEC Path TLV  . . . . . . . . . . . . . . . . . . . .   5
   5.  BFD Reverse Path TLV over Segment Routed MPLS Tunnel with
       Dynamic Control Plane . . . . . . . . . . . . . . . . . . . .   7
   6.  Applicability of BFD Demand Mode in SR-MPLS Domain  . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Non-FEC Path TLV  . . . . . . . . . . . . . . . . . . . .   7
     7.2.  Return Code . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   [RFC5880], [RFC5881], and [RFC5883] defined the operation of
   Bidirectional Forwarding Detection (BFD) protocol between the two
   systems over IP networks.  [RFC5884] and [RFC7726] set rules for
   using BFD Asynchronous mode over point-to-point (p2p) Multiprotocol
   Label Switching (MPLS) Label Switched Path (LSP).  These latter
   standards implicitly assume that the egress BFD peer, which is the
   egress Label Edge Router (LER), will use the shortest path route




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   regardless of the path the ingress LER uses to send BFD Control
   packets towards it.

   This document defines the use of LSP Ping for Segment Routing
   networks over MPLS data plane [RFC8287] to bootstrap and control path
   of a BFD session from the egress to ingress LER using Segment Routing
   tunnel with MPLS data plane (SR-MPLS).

1.1.  Conventions

1.1.1.  Terminology

   BFD: Bidirectional Forwarding Detection

   FEC: Forwarding Equivalence Class

   MPLS: Multiprotocol Label Switching

   SR-MPLS Segment Routing with MPLS data plane

   LSP: Label Switched Path

   LSR Label Switching Router

   LER Label Edge Router

   p2p Point-to-point

   SID Segment Identifier

   SR Segment Routing

1.1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Bootstrapping BFD Session over Segment Routed Tunnel with MPLS Data
    Plane

   Use of an LSP Ping to bootstrap BFD over MPLS LSP is required, as
   documented in [RFC5884], to establish an association between a fault
   detection message, i.e., BFD Control message, and the Forwarding
   Equivalency Class (FEC) of a single label stack LSP in case of
   Penultimate Hop Popping or when the egress Label Switching Router



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   (LSR) distributes the Explicit NULL label to the penultimate hop
   router.  The Explicit NULL label is not advertised as a Segment
   Identifier (SID) by an SR node but, as demonstrated in section 3.1
   [I-D.ietf-spring-segment-routing-mpls] if the operation at the
   penultimate hop is NEXT; then the egress SR node will receive an IP
   encapsulated packet.  Thus the conclusion is that LSP Ping MUST be
   used to bootstrap a BFD session in SR-MPLS domain.

   As demonstrated in [RFC8287], the introduction of Segment Routing
   network domains with an MPLS data plane requires three new sub-TLVs
   that MAY be used with Target FEC TLV.  Section 6.1 addresses use of
   the new sub-TLVs in Target FEC TLV in LSP ping and LSP traceroute.
   For the case of LSP ping, the [RFC8287] states that:

      The initiator, i.e., ingress LSR, MUST include FEC(s)
      corresponding to the destination segment.

      The initiator MAY include FECs corresponding to some or all of
      segments imposed in the label stack by the ingress LSR to
      communicate the segments traversed.

   It has been noted in [RFC5884] that a BFD session monitors for
   defects particular <MPLS LSP, FEC> tuple.  [RFC7726] clarified how to
   establish and operate multiple BFD sessions for the same <MPLS LSP,
   FEC> tuple.  Because only ingress edge router is aware of the SR-
   based explicit route, the egress edge router can associate the LSP
   ping with BFD Discriminator TLV with only one of the FECs it
   advertised for the particular segment.  Thus this document clarifies
   that:

      When LSP Ping is used to bootstraping a BFD session for SR-MPLS
      tunnel the FEC corresponding to the segment to be associated with
      the BFD session MUST be as the very last sub-TLV in the Target FEC
      TLV.

   If the target segment is an anycast prefix segment
   ([I-D.ietf-spring-mpls-anycast-segments]) the corresponding Anycast
   SID MUST be included in the Target TLV as the very last sub-TLV.
   Also, for BFD control packet the ingress SR node MUST use precisely
   the same label stack encapsulation, especially Entropy Label
   ([RFC6790]), as for the LSP ping with the BFD Discriminator TLV that
   bootstrapped the BFD session.  Other operational aspects of using BFD
   to monitor the continuity of the path to the particular Anycast SID,
   advertised by a group of SR-MPLS capable nodes, will be considered in
   the future versions of the document.

   Encapsulation of a BFD Control packet in Segment Routing network with
   MPLS data plane MUST follow Section 7 [RFC5884] when the IP/UDP



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   header used and MUST follow Section 3.4 [RFC6428] without IP/UDP
   header being used.

3.  Use BFD Reverse Path TLV over Segment Routed MPLS Tunnel

   For BFD over MPLS LSP case, per [RFC5884], egress LER MAY send BFD
   control packet to the ingress LER either over IP network or an MPLS
   LSP.  Similarly, for the case of BFD over p2p SR-MPLS tunnel, the
   egress LER MAY route BFD control packet over the IP network, as
   described in [RFC5883], or transmit over a segment tunnel, as
   described in Section 7 [RFC5884].  In some cases, there may be a need
   to direct egress BFD peer to use specific path for the reverse
   direction of the BFD session by using the BFD Reverse Path TLV and
   following all procedures as defined in [I-D.ietf-mpls-bfd-directed].

4.  Use Non-FEC Path TLV

   For the case of MPLS data plane, Segment Routing Architecture
   [RFC8402] explains that "a segment is encoded as an MPLS label.  An
   ordered list of segments is encoded as a stack of labels."  YANG Data
   Model for MPLS Static LSPs [I-D.ietf-mpls-static-yang] models
   outgoing MPLS labels to be imposed as leaf-list [RFC6020], i.e., as
   array of rt-types:mpls-label [RFC8294].

   This document defines new optional Non-FEC Path TLV.  The format of
   the Non-FEC Path TLV is presented in Figure 1

       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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Non-FEC Path TLV Type    |           Length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                             |
       ~                        Non-FEC Path                         ~
       |                                                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Non-FEC Path TLV Format

   Non-FEC Path TLV Type is two octets in length and has a value of TBD1
   (to be assigned by IANA as requested in Section 7.1).

   Length field is two octets long and defines the length in octets of
   the Non-FEC Path field.

   Non-FEC Path field contains a sub-TLV.  Any Non-FEC Path sub-TLV
   (defined in this document or to be defined in the future) for Non-FEC
   Path TLV type MAY be used in this field.  None or one sub-TLV MAY be



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   included in the Non-FEC Path TLV.  If no sub-TLV has been found in
   the Non-FEC Path TLV, the egress BFD peer MUST revert to using the
   reverse path selected based on its local policy.  If there is more
   than one sub-TLV, then the Return Code in echo reply MUST be set to
   value TBD3 "Too Many TLVs Detected" (to be assigned by IANA as
   requested in Table 4).

   Non-FEC Path TLV MAY be used to specify the reverse path of the BFD
   session identified in the BFD Discriminator TLV.  If the Non-FEC Path
   TLV is present in the echo request message the BFD Discriminator TLV
   MUST be present as well.  If the BFD Discriminator TLV is absent when
   the Non-FEC Path TLV is included, then it MUST be treated as
   malformed Echo Request, as described in [RFC8029].

   This document defines Static Routing MPLS Tunnel sub-TLV that MAY be
   used with the Non-FEC Path TLV.  The format of the sub-TLV is
   presented in Figure 2.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | SR MPLS Tunnel sub-TLV Type |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Label Entry 1 (Top Label)                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Label Entry 2                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                             ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Label Entry N (Bottom Label)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


               Figure 2: Segment Routing MPLS Tunnel sub-TLV

   The Segment Routing MPLS Tunnel sub-TLV Type is two octets in length,
   and has a value of TBD2 (to be assigned by IANA as requested in
   Section 7.1).

   The egress LSR MUST use the Value field as label stack for BFD
   control packets for the BFD session identified by the source IP
   address of the MPLS LSP Ping packet and the value in the BFD
   Discriminator TLV.  Label Entries MUST be in network order.








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5.  BFD Reverse Path TLV over Segment Routed MPLS Tunnel with Dynamic
    Control Plane

   When Segment Routed domain with MPLS data plane uses distributed
   tunnel computation BFD Reverse Path TLV MAY use Target FEC sub-TLVs
   defined in [RFC8287].

6.  Applicability of BFD Demand Mode in SR-MPLS Domain

   [I-D.mirsky-bfd-mpls-demand] defines how Demand mode of BFD,
   specified in sections 6.6 and 6.18.4 of [RFC5880], can be used to
   monitor uni-directional MPLS LSP.  Similar procedures can be
   following in SR-MPLS to monitor uni-directional SR tunnels:

   o  ingress SR node bootstraps BFD session over SR-MPLS in Async BFD
      mode;

   o  once BFD session is Up, the ingress node switches the egress BFD
      node into the Demand mode by setting D field in BFD Control packet
      it transmits;

   o  if the egress BFD node detects the failure of the BFD session, it
      sends its BFD control packet to the ingress over the IP network
      with Poll sequence;

   o  if the ingress node receives a BFD control packet from the remote
      node in a Demand mode with Poll sequence and Diag field indicating
      the failure, the ingress transmits BFD control packet with Final
      over IP and switches the BFD over SR-MPLS back into Async mode,
      sending BFD Control packets one per second.

7.  IANA Considerations

7.1.  Non-FEC Path TLV

   IANA is requested to assign new TLV type from the from Standards
   Action range of the registry "Multiprotocol Label Switching
   Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
   TLVs" as defined in Table 1.

               +-------+------------------+---------------+
               | Value | TLV Name         | Reference     |
               +-------+------------------+---------------+
               | TBD1  | Non-FEC Path TLV | This document |
               +-------+------------------+---------------+

                       Table 1: New Non-FEC Path TLV




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   IANA is requested to create new Non-FEC Path sub-TLV registry for the
   Non-FEC Path TLV as described in Table 2.

   +-------------+---------------+-------------------------------------+
   | Range       |  Registration | Note                                |
   |             |   Procedures  |                                     |
   +-------------+---------------+-------------------------------------+
   | 0-16383     |   Standards   | This range is for mandatory TLVs or |
   |             |     Action    | for optional TLVs that require an   |
   |             |               | error message if not recognized.    |
   | 16384-31743 | Specification | Experimental RFC needed             |
   |             |    Required   |                                     |
   | 32768-49161 |   Standards   | This range is for optional TLVs     |
   |             |     Action    | that can be silently dropped if not |
   |             |               | recognized.                         |
   | 49162-64511 | Specification | Experimental RFC needed             |
   |             |    Required   |                                     |
   | 64512-65535 |  Private Use  |                                     |
   +-------------+---------------+-------------------------------------+

                  Table 2: Non-FEC Path sub-TLV registry

   IANA is requested to allocate the following values from the Non-FEC
   Path sub-TLV registry as defined in Table 3.

      +-------+-------------------------------------+---------------+
      | Value | Description                         | Reference     |
      +-------+-------------------------------------+---------------+
      | 0     | Reserved                            | This document |
      | TBD2  | Segment Routing MPLS Tunnel sub-TLV | This document |
      | 65535 | Reserved                            | This document |
      +-------+-------------------------------------+---------------+

                Table 3: New Segment Routing Tunnel sub-TLV

7.2.  Return Code

   IANA is requested to create Non-FEC Path sub-TLV sub-registry for the
   new Non-FEC Path TLV and assign a new Return Code value from the
   "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
   Ping Parameters" registry, "Return Codes" sub-registry, as follows
   using a Standards Action value.









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           +--------+-------------------------+---------------+
           | Value  | Description             | Reference     |
           +--------+-------------------------+---------------+
           | X TBD3 | Too Many TLVs Detected. | This document |
           +--------+-------------------------+---------------+

                         Table 4: New Return Code

8.  Security Considerations

   Security considerations discussed in [RFC5880], [RFC5884], [RFC7726],
   and [RFC8029] apply to this document.

9.  Acknowledgments

   TBD

10.  References

10.1.  Normative References

   [I-D.ietf-mpls-bfd-directed]
              Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Directed Return
              Path", draft-ietf-mpls-bfd-directed-09 (work in progress),
              August 2018.

   [I-D.ietf-spring-segment-routing-mpls]
              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-14
              (work in progress), June 2018.

   [I-D.mirsky-bfd-mpls-demand]
              Mirsky, G., "BFD in Demand Mode over Point-to-Point MPLS
              LSP", draft-mirsky-bfd-mpls-demand-03 (work in progress),
              June 2018.

   [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>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.





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   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <https://www.rfc-editor.org/info/rfc5881>.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <https://www.rfc-editor.org/info/rfc5883>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [RFC6428]  Allan, D., Ed., Swallow, G., Ed., and J. Drake, Ed.,
              "Proactive Connectivity Verification, Continuity Check,
              and Remote Defect Indication for the MPLS Transport
              Profile", RFC 6428, DOI 10.17487/RFC6428, November 2011,
              <https://www.rfc-editor.org/info/rfc6428>.

   [RFC7726]  Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
              Aldrin, "Clarifying Procedures for Establishing BFD
              Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726,
              DOI 10.17487/RFC7726, January 2016,
              <https://www.rfc-editor.org/info/rfc7726>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [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>.

   [RFC8287]  Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
              N., Kini, S., and M. Chen, "Label Switched Path (LSP)
              Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
              IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
              Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
              <https://www.rfc-editor.org/info/rfc8287>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.




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10.2.  Informative References

   [I-D.ietf-mpls-static-yang]
              Saad, T., Raza, K., Gandhi, R., Liu, X., and V. Beeram, "A
              YANG Data Model for MPLS Static LSPs", draft-ietf-mpls-
              static-yang-05 (work in progress), February 2018.

   [I-D.ietf-spring-mpls-anycast-segments]
              Sarkar, P., Gredler, H., Filsfils, C., Previdi, S.,
              Decraene, B., and M. Horneffer, "Anycast Segments in MPLS
              based Segment Routing", draft-ietf-spring-mpls-anycast-
              segments-02 (work in progress), January 2018.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC8294]  Liu, X., Qu, Y., Lindem, A., Hopps, C., and L. Berger,
              "Common YANG Data Types for the Routing Area", RFC 8294,
              DOI 10.17487/RFC8294, December 2017,
              <https://www.rfc-editor.org/info/rfc8294>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


   Jeff  Tantsura
   Nuage Networks

   Email: jefftant.ietf@gmail.com


   Ilya Varlashkin
   Google

   Email: Ilya@nobulus.com





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   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com















































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