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Versions: 00 01

SPRING Working Group                                               C. Li
Internet-Draft                                       Huawei Technologies
Intended status: Informational                                  A. Sawaf
Expires: May 7, 2020                               Saudi Telecom Company
                                                                   R. Hu
                                                                   Z. Li
                                                     Huawei Technologies
                                                        November 4, 2019


A Framework for Constructing Service Function Chaining Systems Based on
                            Segment Routing
           draft-li-spring-sr-sfc-control-plane-framework-01

Abstract

   Segment Routing (SR) allows for a flexible definition of end-to-end
   paths by encoding paths as sequences of topological sub-paths, called
   "segments".  Segment routing architecture can be implemented over an
   MPLS data plane as well as an IPv6 data plane.

   Service Function Chaining (SFC) provides support for the creation of
   composite services that consist of an ordered set of Service
   Functions (SF) that are to be applied to packets and/or frames
   selected as a result of classification.

   SFC can be implemented based on several technologies, such as Network
   Service Header (NSH) and SR.  This document describes a framework for
   constructing SFC based on Segment Routing.  The document reviews the
   control plane solutions for route distribution of service function
   instance and service function path, and steering packets into a
   service function chain.

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."




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   This Internet-Draft will expire on May 7, 2020.

Copyright Notice

   Copyright (c) 2019 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
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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.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview of SR Based SFC Control Plane  . . . . . . . . . . .   4
   3.  Stateless SR Based SFC  . . . . . . . . . . . . . . . . . . .   6
     3.1.  Service Function Instance Route Distribution  . . . . . .   6
     3.2.  Service Function Path Route Distribution  . . . . . . . .   7
     3.3.  Steer Packets into SFC  . . . . . . . . . . . . . . . . .   7
   4.  Stateful SR Based SFC . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Service Function Route Distribution . . . . . . . . . . .   8
     4.2.  Service Function Path Route Distribution  . . . . . . . .   8
     4.3.  Steer Packets into SFC  . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Segment routing (SR) [RFC8402] is a source routing paradigm that
   explicitly indicates the forwarding path for packets at the ingress
   node by inserting an ordered list of instructions, called segments.
   When segment routing is deployed on MPLS data plane, it is called SR-
   MPLS [I-D.ietf-spring-segment-routing-mpls].  When segment routing is
   deployed on IPv6 data plane, it is called SRv6
   [I-D.ietf-6man-segment-routing-header].



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   Service Function Chaining (SFC) [RFC7665] provides an architecture
   that supports the creation of composite service that consist of an
   ordered set of Service Functions (SF) that are to be applied to
   packets and/or frames selected as a result of classification.

   SFC can be implemented based on Network Service Header [RFC8300].  In
   NSH-based SFC, per-SFC state, such as a mapping between Service Path
   Identifier (SPI) and Service Index (SI) to next-hop forwarding, needs
   to be maintained on nodes along the Service Function Path(SFP), and
   it can therefore, be termed as "stateful SFC".
   [I-D.ietf-bess-nsh-bgp-control-plane] defines the use of BGP as a
   control plane for networks that support SFC based on NSH and MPLS.
   The document introduces a new BGP address family called the SFC AFI/
   SAFI with two route types: Service Function Instance Route (SFIR) and
   Service Function Path Route (SFPR).  An NSH or MPLS based SFC can be
   constructed based on the information of SFIR and SFPR.

   SFC can also be instantiated based on SR.  In SR, the forwarding path
   is explicitly encoded into the packets on the SR source node.  In SR-
   based SFC, an SFC can be represented by a SID list explicitly
   indicated by the source SR node.  The SID in SID list may need to be
   associated with service information in order to indicate network
   service, such as Deep Packet Inspection (DPI).  Therefore, no per-SFC
   state needs to be maintained along with the SFP, and it can therefore
   be termed "stateless SFC".

   In order to construct SR-based SFC, several mechanisms are proposed,
   including the mechanisms of SFIR and SFPR distribution, as well as
   the mechanism of steering packets into an SFP.  This document reviews
   these solutions to describe a framework for the construction of an
   SFC system based on Segment Routing.

1.1.  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.

1.2.  Terminology

   MPLS: Multiprotocol Label Switching.

   SID: Segment Identifier.

   SR: Segment Routing.




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   SR-MPLS: Segment Routing with MPLS data plane.

   SRH: Segment Routing Header.

   SFIR: Service Function Instance Route

   SFPR: Service Function Path Route

   Further, this document makes use of the terms defined in [RFC7665]
   and [I-D.ietf-spring-sr-service-programming].

2.  Overview of SR Based SFC Control Plane

   As per [RFC7665], the architecture of SFC consists of classifiers,
   Service Function Forwarders (SFFs), Service Functions (SFs) and SFC
   Proxies.  This is illustrated in Figure 1.

                                       +-----+         +-----+   +-----+
                                       |     |         | SFC |   |     |
                                       | SF1 |         |Proxy|---| SF2 |
                                       +-----+         +-----+   +-----+
                                          |               |
     +--------------+                     |               |
     |   Service    |       SFC        +------+        +------+
     |Classification|  Encapsulation   | SFF1 |        | SFF2 |
 --->|   Function   |+---------------->|      |--------|      |------->
     |              |                  |      |        |      |
     +--------------+                  +------+        +------+

          SFC-enabled Domain


                       Figure 1. SFC Architecture


   In order to construct an SFC, SFIR and SFPR should be distributed to
   classifiers and SFFs.  Also, the rules of steering packets into
   specific SFPs should be configured at the classifier.
   [I-D.ietf-bess-nsh-bgp-control-plane].

   In SR, a source node can explicitly indicate the forwarding path for
   packets by inserting an ordered list of instructions.  These packet
   steering policies, known as SR policy, can be installed by a central
   controller via BGP [I-D.ietf-idr-segment-routing-te-policy] or other
   mechanisms.

   When SFC is constructed based on SR, SFPR and packet steering rules
   can be installed by SR policy at the ingress node, which plays the



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   role of classifier in the SFC architecture.  In other words, SFPR
   does not need to be distributed to all the nodes along the SFP.  The
   architecture of SR based SFC is illustrated in Figure 2.

         +-----+                       +-----+         +-----+   +-----+
         |     |                       |     |         | SR  |   |     |
         |SR-C |                       | SF1 |         |Proxy|---| SF2 |
         +-----+                       +-----+         +-----+   +-----+
            |                             |               |
            |                             |               |
     +--------------+                  +------+        +------+
     |              |   SFC Encap/SR   | SFF1/|        | SFF2/|
 --->|CF/SR ingress |+---------------->|  SR  |--------|  SR  |------->
     |              |                  |      |        |      |
     +--------------+                  +------+        +------+

          SFC-enabled Domain

                     Figure 2. SR based SFC architecture.

   o  CF/SR ingress: an SR ingress node plays the role of Classifier in
      the SFC architecture, and it connects to an SR controller, where
      the SR policies originate.

   o  SR-C: SR Controller (SR-C) is connected to the SR ingress node,
      and may be attached to any node in the network.  SR-C is capable
      of discovering topology, and calculating constrained paths for
      SFCs.

   o  SFF/SR nodes: the SFF component in SFC architecture, which enables
      SR to steer packets to SFs.

   o  SFn: Service Functions, can be SR-aware or SR-unaware.  If an SF
      is SR-unaware then SR proxy is needed.

   o  SR proxy: A proxy between SFF/SR nodes and SR-unaware SF.

   There are two solutions to encode SFC in the SR data plane.
   [I-D.ietf-spring-sr-service-programming] defines data plane
   functionality required to implement service segments and achieve
   service programming in SR-enabled MPLS and IP networks.  It can be
   termed "Stateless SFC" since no per-SFC state is maintained on the SR
   nodes along the SFP.

   The second solution can be termed "Stateful SFC"
   [I-D.ietf-spring-nsh-sr], since it still maintains per-SFC state on
   nodes.  [I-D.ietf-spring-nsh-sr]describes two modes of operation:




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   o  NSH-based SFC with SR-based transport tunnel: SR is used as the
      transport tunnel to route packets between classifier and SFF or
      SFFs.  Service plane routing relies on NSH.

   o  SR-based SFC with Integrated NSH Service Plane: The SFP is encoded
      within the SR segment-list, while the NSH only maintains the
      service plane context information, which will be used at NSH-aware
      SFs, and at SFFs as a pointer to cache SR segment-lists.

   In order to support these data plane encodings, control plane
   mechanisms are required.  The existing control plane mechanisms are
   shown in table 1.

    +------------------------------------------------------------+
    | SR based SFC      |   SFIR    |    SFPR   | Steering policy|
    +-------------------+-----------+-----------+----------------+
    |                   |   BGP     |    BGP    |      BGP       |
    |Stateless          |   BGP-LS  |    PCEP   |      PCEP      |
    |                   |   IGP     |           |                |
    +-------------------+-----------+-----------+----------------+
    |NSH-based SFC      |   BGP     |    BGP    |      BGP       |
    |with SR-based      |           |    PCEP   |                |
    |transport tunnel   |           |           |                |
    |                   |           |           |                |
    |                   |           |           |                |
    +-------------------+-----------+-----------+----------------+
    |SR-based SFC       |   BGP     |    BGP    |      BGP       |
    |with Integrated    |   BGP-LS  |    PCEP   |      PCEP      |
    |NSH Service Plane  |   IGP     |           |                |
    |                   |           |           |                |
    +-------------------+-----------+-----------+----------------+
             Table 1. SR based SFC Control Plane Solutions

3.  Stateless SR Based SFC

   As describe in [I-D.ietf-spring-sr-service-programming], service
   instances are associated with a segment, called a service SID.  These
   service SIDs are leveraged as part of a SID-list to steer packets
   through the corresponding services

3.1.  Service Function Instance Route Distribution

   To associate a segment with a service, service information, such as
   Service Function Type (SFT), should be included in segment
   distribution.  [I-D.dawra-idr-bgp-ls-sr-service-segments] specifies
   the extensions to BGP-LS for discovery and advertisement of service
   segments to enable setup of service programming paths using Segment
   Routing.  [I-D.dawra-idr-bgp-ls-sr-service-segments] extends SRv6



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   Node SID TLV [I-D.ietf-idr-bgpls-srv6-ext] and SR-MPLS SID/ Label TLV
   [I-D.ietf-idr-bgp-ls-segment-routing-ext] to associate the Service
   SID Value with Service-related Information using Service Chaining
   Sub-TLV.  The Service Chaining Sub-TLV contains information of
   Service SID value, Function Identifier (Static Proxy, Dynamic Proxy,
   Shared Memory Proxy, Masquerading Proxy, SR Aware Service Etc.),
   Service Type (DPI, Firewall, Classifier, LB etc.), Traffic Type (IPv4
   OR IPv6 OR Ethernet) and Opaque Data (such as brand and version,
   other extra information).  This extension works for both SR- MPLS and
   SRv6.

   [I-D.ietf-bess-nsh-bgp-control-plane] proposes a BGP-based SFC
   control plane solution, and it works for SR-MPLS as well.  Service
   function instance route distribution can use SFIR in SFC AFI/SAFI.
   SFPR and steering rules for the classifier can be distributed by SR
   policy, which is defined in [I-D.ietf-idr-segment-routing-te-policy].
   BGP control plane of SRv6-based SFC still needs to be defined.

   IGP extensions are proposed by [I-D.xu-isis-service-function-adv] and
   [I-D.xu-ospf-service-function-adv].  In IS-IS solution, SFFs within
   the SFC domain need to advertise each SF they are offering by using a
   new sub-TLV of the IS-IS Router CAPABILITY TLV [RFC4971].  This new
   sub-TLV is called Service Function sub-TLV, and it can appear
   multiple times within a given IS-IS Router CAPABILITY TLV or when
   more than one SF needs to be advertised.  OSPF extensions are
   similar, and use the OSPF Router Information (RI) Opaque LSA
   [RFC4970] to carry Service Function sub-TLV.

   However, due to IGP flooding issues, IGP extensions are not very
   appropriate, and the drafts have expired for a long time.

3.2.  Service Function Path Route Distribution

   With SR, the SFPR does not need to be distributed to nodes along the
   SFP but only to the ingress node.  SFPR and steering rules for the
   classifier can be distributed by SR policy.  The BGP extension is
   defined in [I-D.ietf-idr-segment-routing-te-policy].  The PCEP
   extension is defined in [I-D.barth-pce-segment-routing-policy-cp].

3.3.  Steer Packets into SFC

   In SR, packet steering rules are learned through SR policy.  Thus,
   there is no need to install other rules in the classifier, which is
   the SR source node.







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4.  Stateful SR Based SFC

   "Stateful SFC" [I-D.ietf-spring-nsh-sr] proposes two modes of SR
   based SFC:

   o  NSH-based SFC with SR-based transport tunnel

   o  SR-based SFC with Integrated NSH Service Plane

4.1.  Service Function Route Distribution

   For NSH-based SFC with SR-based transport tunnel, service information
   is maintained by NSH while SR is only used for transport between
   SFFs, so [I-D.ietf-bess-nsh-bgp-control-plane] can be used for this
   mode.

   To indicate NSH, an SFF label [I-D.ietf-mpls-sfc-encapsulation]
   should be inserted as the last label in the label stack in SR-MPLS.
   The control plane of SFF is also described in
   [I-D.ietf-bess-nsh-bgp-control-plane].  For choosing/configuring SR
   as the transport tunnel, BGP route of SFF's BGP Tunnel Encapsulation
   Attribute Type should be "SR TE Policy Type"
   [I-D.ietf-idr-segment-routing-te-policy].  For SR-based SFC with
   Integrated NSH Service Plane, there is no control plane solution as
   yet defined.

4.2.  Service Function Path Route Distribution

   Same as SFIR distribution, SFPR BGP distribution in NSH-based SFC
   with SR-based transport tunnel is identical to the mechanism defined
   in [I-D.ietf-bess-nsh-bgp-control-plane].  PCEP extension for SFPR
   distribution can reuse the NSH based SFC extension defined in
   [I-D.wu-pce-traffic-steering-sfc].  For SR-based SFC with Integrated
   NSH Service Plane, control plane solution is to be added in other
   documents.

4.3.  Steer Packets into SFC

   For NSH-based SFC with SR-based transport tunnel, it is the same with
   the NSH based SFC.  The Classifier is responsible for determining to
   which packet flow a packet belongs (usually by inspecting the packet
   header), imposing an NSH, and initializing the NSH with the SPI of
   the selected SFP and the SI of its first hop
   [I-D.ietf-bess-nsh-bgp-control-plane].  For SR-based SFC with
   Integrated NSH Service Plane, control plane solution is to be added
   in other document.





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5.  IANA Considerations

   This document does not require any IANA actions.

6.  Security Considerations

   This document does not introduce additional security requirements and
   mechanisms.

7.  Acknowledgements

   TBA

8.  References

8.1.  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>.

   [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>.

8.2.  Informative References

   [I-D.barth-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Li, C., and H.
              Bidgoli, "PCEP extension to support Segment Routing Policy
              Candidate Paths", draft-barth-pce-segment-routing-policy-
              cp-04 (work in progress), October 2019.

   [I-D.dawra-idr-bgp-ls-sr-service-segments]
              Dawra, G., Filsfils, C., daniel.bernier@bell.ca, d.,
              Uttaro, J., Decraene, B., Elmalky, H., Xu, X., Clad, F.,
              and K. Talaulikar, "BGP-LS Advertisement of Segment
              Routing Service Segments", draft-dawra-idr-bgp-ls-sr-
              service-segments-02 (work in progress), July 2019.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.





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   [I-D.ietf-bess-nsh-bgp-control-plane]
              Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
              Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess-
              nsh-bgp-control-plane-12 (work in progress), August 2019.

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
              (work in progress), June 2019.

   [I-D.ietf-idr-bgpls-srv6-ext]
              Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
              daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link
              State Extensions for SRv6", draft-ietf-idr-bgpls-
              srv6-ext-01 (work in progress), July 2019.

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Mattes, P., Rosen, E., Jain,
              D., and S. Lin, "Advertising Segment Routing Policies in
              BGP", draft-ietf-idr-segment-routing-te-policy-07 (work in
              progress), July 2019.

   [I-D.ietf-mpls-sfc-encapsulation]
              Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
              "MPLS Transport Encapsulation For The SFC NSH", draft-
              ietf-mpls-sfc-encapsulation-04 (work in progress), March
              2019.

   [I-D.ietf-spring-nsh-sr]
              Guichard, J., Song, H., Tantsura, J., Halpern, J.,
              Henderickx, W., Boucadair, M., and S. Hassan, "Network
              Service Header (NSH) and Segment Routing Integration for
              Service Function Chaining (SFC)", draft-ietf-spring-nsh-
              sr-01 (work in progress), October 2019.

   [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-22
              (work in progress), May 2019.

   [I-D.ietf-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
              d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
              Henderickx, W., and S. Salsano, "Service Programming with
              Segment Routing", draft-ietf-spring-sr-service-
              programming-00 (work in progress), October 2019.



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   [I-D.wu-pce-traffic-steering-sfc]
              Wu, Q., Dhody, D., Boucadair, M., Jacquenet, C., and J.
              Tantsura, "PCEP Extensions for Service Function Chaining
              (SFC)", draft-wu-pce-traffic-steering-sfc-12 (work in
              progress), June 2017.

   [I-D.xu-isis-service-function-adv]
              Xu, X., Wu, N., Shah, H., and L. Contreras, "Advertising
              Service Functions Using IS-IS", draft-xu-isis-service-
              function-adv-05 (work in progress), May 2017.

   [I-D.xu-ospf-service-function-adv]
              Xu, X., Wu, N., Shah, H., and L. Contreras, "Advertising
              Service Functions Using OSPF", draft-xu-ospf-service-
              function-adv-02 (work in progress), June 2014.

   [RFC4970]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
              2007, <https://www.rfc-editor.org/info/rfc4970>.

   [RFC4971]  Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
              "Intermediate System to Intermediate System (IS-IS)
              Extensions for Advertising Router Information", RFC 4971,
              DOI 10.17487/RFC4971, July 2007,
              <https://www.rfc-editor.org/info/rfc4971>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

   [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>.

Authors' Addresses

   Cheng Li
   Huawei Technologies

   Email: chengli13@huawei.com



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Internet-Draft         SR based SFC Control Plane          November 2019


   Ahmed El Sawaf
   Saudi Telecom Company
   Riyadh
   Saudi Arabia

   Email: aelsawaf.c@stc.com.sa


   Ruizhao Hu
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: huruizhao@huawei.com


   Zhenbin Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: lizhenbin@huawei.com



























Li, et al.                 Expires May 7, 2020                 [Page 12]


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