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Versions: 00 01

LSR Working Group                                                J. Dong
Internet-Draft                                                 S. Bryant
Intended status: Standards Track                     Huawei Technologies
Expires: April 25, 2019                                 October 22, 2018


         IGP Extensions for Segment Routing based Enhanced VPN
                   draft-dong-lsr-sr-enhanced-vpn-01

Abstract

   Enhanced VPN (VPN+) is an enhancement to VPN services to support the
   needs of new applications, particularly including the applications
   that are associated with 5G services.  These applications require
   better isolation and have more stringent performance requirements
   than that can be provided with traditional overlay VPNs.  An enhanced
   VPN may form the underpin of 5G transport network slicing, and will
   also be of use in its own right.  This document describes how Multi-
   Topology Routing (MTR) as described in RFC 5120, RFC 4915 and
   RFC5340, can be extended to signal the network resources allocated in
   the underlay network to construct the customized virtual networks for
   enhanced VPN services, together with the Segment Routing Identifiers
   (SIDs) used to identify and access the network resources allocated
   for each virtual network in the data plane.

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
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   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 April 25, 2019.

Copyright Notice

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





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   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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Specification of Requirements . . . . . . . . . . . . . . . .   3
   3.  Overview of Approach  . . . . . . . . . . . . . . . . . . . .   3
   4.  SR Virtual Topology with Resource Guarantee . . . . . . . . .   4
     4.1.  Topology specific Link Resource Allocation and
           Identification  . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Topology specific Node Resource Allocation and
           Identification  . . . . . . . . . . . . . . . . . . . . .   6
   5.  Multiple Services in SR Virtual Topology  . . . . . . . . . .   6
     5.1.  Common Service Types  . . . . . . . . . . . . . . . . . .   7
       5.1.1.  Best Effort . . . . . . . . . . . . . . . . . . . . .   7
       5.1.2.  Assured Bandwidth . . . . . . . . . . . . . . . . . .   7
       5.1.3.  Deterministic . . . . . . . . . . . . . . . . . . . .   8
   6.  Topology and Algorithm  . . . . . . . . . . . . . . . . . . .   8
   7.  SRv6 Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Fast Repair . . . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  LAN interface . . . . . . . . . . . . . . . . . . . . . . . .  10
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  10
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The framework for an enhanced virtual private network (VPN+) is
   described in [I-D.dong-teas-enhanced-vpn].

   Driven largely by needs arising from the 5G mobile network design,
   the concept of network slicing has gained traction.  There is a need
   to create a VPN service with enhanced isolation and performance
   characteristics.  Specifically, there is a need for a transport
   network to support a set of virtual networks, each of which provides
   the client with some dedicated (private) network resources drawn from



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   a shared pool.  The tenant of such a virtual network can require a
   degree of isolation and performance that previously could only be
   satisfied by dedicated networks.  Additionally the tenant may ask for
   some level of control of their virtual networks e.g. to customize the
   service paths in their network slices.

   These properties cannot be met with pure overlay networks, as they
   require tighter coordination and integration between the underlay and
   the overlay network.  [I-D.dong-teas-enhanced-vpn] provides the
   framework of enhanced VPN and describes the candidate component
   technologies.  [I-D.dong-spring-sr-for-enhanced-vpn] describes how
   segment routing (SR) [I-D.ietf-spring-segment-routing] is used to
   construct the required virtual networks with the network resources
   allocated for enhanced VPN services.

   This document describes how Multi-Topology Routing (MTR), as
   described in [RFC5120] [RFC4915] and [RFC5340] , is extended to
   signal the resources allocated in the underlay to construct the
   virtual networks for enhanced VPN services, together with the segment
   routing identifiers (SIDs) used to identify and access the resource
   allocated for different virtual networks in the data plane.  The
   mechanism is applicable to both SR with MPLS data plane and SR with
   IPv6 data plane (SRv6).

2.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Overview of Approach

   To meet the requirement of enhance VPN services, a number of virtual
   networks can be created, each representing a subset of the underlay
   network topology and resources to be used by a specific customer.  In
   a 5G context, each virtual network is considered as a network slice
   which serves one slice tenant.  Depending on the service
   requirements, different virtual networks can either share the same
   physical links or nodes, or use separate links or nodes in the
   network, while the required level of isolation and performance SHOULD
   be guaranteed in both cases.

   IGP multi-topology routing can be seen as a candidate mechanism to
   create multiple network topologies in one network.  Different from
   the traditional multi-topology mechanism, which only provides logical
   topological isolation, in the proposed mechanism network resources
   can be partitioned and allocated to different virtual network
   topologies to meet the isolation and performance requirements of



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   enhanced VPN.  Service in one virtual topology can be instructed to
   be processed only using the network resources allocated to this
   virtual topology.  This is achieved by using multi-topology routing
   (MTR) together with segment routing, and extending the SR paradigm to
   use Segment Identifiers (SIDs) to identify different set of resources
   allocated from a particular network element (e.g. link or node).
   Different set of SIDs are associated with different virtual
   topologies, and are used to create the SID lists within different
   virtual topologies.  In some cases, it is also possible for several
   virtual network topologies to share some network resources, this can
   be achieved by using the same SR SIDs between those topologies.  The
   detailed mechanism of resource sharing will be described in a future
   version.

   Within one SR virtual network, one or more type of services can be
   deployed using the resources allocated to that topology, some of
   which may have different characteristics and require dedicated
   resources or special treatment.  The concept is similar to the DS-TE
   model [RFC4124] of RSVP-TE based mechanism, while in this case the SR
   paradigm is applied, which avoids the introduction of per-path state
   into the network.

   In general this approach applies to both IS-IS and OSPF, while the
   specific protocol extensions and encodings are different.  In the
   current version of this document, the required IS-IS extensions are
   described.  The required OSPF extensions will be described in a
   future version.

4.  SR Virtual Topology with Resource Guarantee

   As described in [I-D.ietf-isis-segment-routing-extensions], IS-IS
   TLV-222 (MT-ISN) and TLV-223 (MT IS Neighbor Attribute) have been
   enhanced to carry the Adj-SID sub-TLV, and TLV-235 (Multitopology
   IPv4 Reachability) and TLV-237 (Multitopology IPv6 IP Reachability)
   have been enhanced to carry the Prefix-SID sub-TLV.  With these
   enhancements, dedicated Segment Identifiers (SIDs) can be assigned
   for each SR virtual network topology.  The topology-specific SIDs can
   be used as distinguisher in packet forwarding of different
   topologies.

   This section specifies the necessary extensions to enable the
   deployment of resource guaranteed SR virtual topologies.  Each
   virtual topology can be allocated with a particular partition of
   network resources from the underlay network, the SIDs can be used to
   identify the set of resources allocated for different virtual
   topologies on each involved network element.





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4.1.  Topology specific Link Resource Allocation and Identification

   A network link can participate in one or multiple SR virtual
   topologies, each virtual topology is assigned with a dedicated adj-
   SID.  In order to describe the amount of link resource allocated to a
   particular SR virtual topology, a new IS-IS sub-TLV called "SR
   Bandwidth" sub-TLV is defined:

   The SR-Bandwidth sub-TLV is an optional sub-TLV carrying the
   aggregated bandwidth allocated to a particular SR adj-SID, which is
   associated witha particular virtual topology.  In the data plane, the
   allocated bandwidth and the associated functional components are
   identified by the adj-SID of the virtual topology.  This sub-TLV may
   be advertised as a sub-TLV of the following TLVs:

     TLV-22  (Extended IS reachability) [RFC5305]

     TLV-23 (IS Neighbor Attribute) [RFC5311]

     TLV-141 (inter-AS reachability information) [RFC5316]

     TLV-222 (Multitopology IS)[RFC5120]

     TLV-223 (Multitopology IS Neighbor Attribute) [RFC5311]

   The SR bandwidth sub-TLV can appear at most once for a particular
   topology.  Multiple SR Bandwidth sub-TLVs MAY be associated with a
   single IS neighbor.

   The following format is defined for the SR Bandwidth sub-TLV:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Type        |     Length    |      Bandwidth
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Bandwidth Cont      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     SR Bandwidth sub-TLV

   where:

   Type: TBD, to be assigned by IANA.

   Length: variable.

   The SR bandwidth is encoded in 32 bits in IEEE floating
   point format.  The units are bytes (not bits!) per second.



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   [I-D.ietf-teas-sr-rsvp-coexistence-rec] describes several options for
   traffic engineering in networks where RSVP-TE and SR LSPs coexist.
   Note that section 3.1 of [I-D.ietf-teas-sr-rsvp-coexistence-rec]
   proposes to partition the network bandwidth between RSVP-TE and SR.
   The can be considered as a special case of creating one default SR
   virtual topology with dedicated bandwidth allocated, so that the
   network resources and operation of SR are isolated from the RSVP-TE
   based LSPs.

4.2.  Topology specific Node Resource Allocation and Identification

   A network node can participate in one or multiple SR virtual
   topologies, each virtual topology is assigned with a dedicated node-
   SID.  In SR loose path forwarding, the topology specific node-SIDs
   can be used by transit network nodes to identify the virtual topology
   the packet belongs to, so as to steer the packet through the set of
   link resources allocated to the identified virtual topology.  A
   prefix-SID sub-TLV describing the dedicated node-SID for each virtual
   topology is needed, this is supported in
   [I-D.ietf-isis-segment-routing-extensions] for SR using MPLS data
   plane.  The mechanism for SRv6 is described in section 7.

   In addition, similar to the allocation of link resource to virtual
   topologies, it is possible to allocate a subset of nodal resources to
   a particular virtual topology to ensure end-to-end service delivery.
   The nodal resources can be identified by topology specific node-SIDs.
   During packet forwarding, the node SIDs can be used to steer a packet
   through the set of nodal resources allocated to this topology.
   Optional sub-TLVs describing the resources allocated at the node
   level for a particular virtual topology can be defined in future.
   The specification of nodal resources is for further study.

5.  Multiple Services in SR Virtual Topology

   Within one SR virtual topology, one or more types of service can be
   deployed using the resources allocated to this virtual topology.
   Each service type can have specific resource constraints and
   characteristics.  The concept is similar to the DS-TE model [RFC4124]
   of RSVP-TE based mechanism, while in this case the SR paradigm is
   applied, which avoids the introduction of per-flow state into the
   network.

   Some mechanism is needed to identify different service types and
   specify the different service characteristics within one virtual
   topology.  The detailed protocol extensions will be provided in a
   future version.





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5.1.  Common Service Types

   A service type is fundamentally the sum of the properties of a group
   of services.  The authors considered specifically creating a number
   of specific service types within the protocol but concluded that this
   was meaningless.  The following sections show how a number of well
   known service types can be constructed.

5.1.1.  Best Effort

   Best effort service can be the only service type in a particular
   virtual topology.  In this case, all of the resources allocated to
   this virtual topology instance are available to the best effort
   services.

   Where there are multiple service types being carried in a virtual
   topology, best effort service will be transmitted over the links and
   nodes when there is an opportunity.  The maximum resources which can
   be used by best effort service may be constrained to a subset of the
   topology resource.  The Traffic Class (TC) of the best effort service
   SHOULD be set to lower than any other service types.

   In the data plane, the SID and the Traffic Class value in the packet
   can be used to identify the service type and steer the best effor
   packets into the correct forwarding resources, such as queues.

   Best effort services may or may not be protected at the discretion of
   the network operator.

5.1.2.  Assured Bandwidth

   An Assured Bandwidth service is one in which the bandwidth is assured
   but the latency is not.  Thus, some bandwidth can be allocated to the
   assured bandwidth service, and traffic up to that bandwidth will be
   transmitted over the service, but the traffic may be delayed by other
   traffic.

   It is likely that the assured bandwidth service will be carried in a
   virtual topology together with other service types, such as the best
   effort service.  The maximum resources which can be used by assured
   bandwidth service SHOULD be constrained to a subset of the topology
   resource.

   There will frequently be more than one assured bandwidth service
   running on a topology, and the Traffic Class (TC) could be used to
   determine how the various services compete for access to the link.
   Whilst the bandwidth is assured over the long term, over the short
   term it is not and such services will interact with similar and lower



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   service classes in such a way that packet delay and jitter is not
   assured.

   In the data plane, the SID and the Traffic Class value in the packet
   can be used to identify the service type and priority and steer the
   assured bandwidth service packets into the correct forwarding
   resources, such as queues.

5.1.3.  Deterministic

   A Deterministic service is a service that may have controlled delay/
   jitter characteristics and/or an enhanced packet delivery assurance.
   Delay/Jitter may be addressable through the provision of sufficient
   bandwidth, or it may require some form of packet scheduling.
   Enhanced delivery assurance may require the use of packet replication
   and elimination mechanism.  The design of a deterministic network is
   discussed in [I-D.ietf-detnet-architecture].  Note that delay
   protection and delivery protection are orthogonal characteristics and
   a service may provide just one of the characteristics or it may
   provide both.

   The details of a deterministic service will be provided in a future
   version.  Such a service may be specified using the TLVs defined in
   [I-D.geng-detnet-info-distribution]

6.  Topology and Algorithm

   In the proposed mechanism, SR is used with IGP multi-topology to
   create one or more SR virtual topologies, each associated with a set
   of network resources allocated for the virtual topology.  The service
   paths used between nodes in one virtual topology are not constrained
   to be shorted path by IGP metric, and can be any non-looping path
   that best suits the needs of the service.  These paths may be imposed
   by the network controller, or calculated using a distributed method.
   For example, different SR algorithms as defined in
   [I-D.ietf-isis-segment-routing-extensions] can be used within one
   virtual topology.  The Flex-Algo mechanism defined in
   [I-D.ietf-lsr-flex-algo] may also be used in one virtual topology to
   meet different service requirements.

7.  SRv6 Considerations

   The mechanism to create virtual network topologies with guaranteed
   resource using SRv6 data plane is similar to SR with MPLS data plane,
   while there are some differences to be considered.

   As described in [I-D.filsfils-spring-srv6-network-programming], an
   SRv6 SID is represented with the format of LOC:FUNCT, where LOC is



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   the locator field, and FUNCT is the function field. the Locator of
   the SID is routable and leads to the node which instantiates that
   SID.  The function of the SID is an opaque identification of a local
   function bound to the SID, which means the function field can only be
   parsed by the node which instantiates the SRv6 SID.  In order to
   build multiple virtual topologies with SRv6 data plane, all the nodes
   in one particular topology must have consistent forwarding behavior.
   On one node which participate in multiple topologies, it MUST to be
   able to distinguish packets of different topologies to perform
   correct packet forwarding.

   Taking the above into consideration, each node MUST allocate
   dedicated SRv6 locator for each virtual topology it participates in,
   the mapping of locator to topology MUST be advertised into the
   network.  For one virtual topology, all the SRv6 SIDs on a node MUST
   be allocated from the SID space identified by the topology-specific
   locator which is associated with the topology.

   In the latest version of [I-D.bashandy-isis-srv6-extensions], the
   SRv6 Locator TLV is defined to advertise the locators for each
   topology/algorithm pair.  The SRv6 SIDs are defined as sub-TLVs of
   SRv6 Locator TLV, except for SRv6 End.X SIDs/LAN End.X SIDs which are
   associated with a specific Neighbor/Link.  Such protocol extensions
   can support the advertisement of topology-specific locators, and the
   SRv6 SIDs which inherits the topology information from the locator.

   In order to advertise the SRv6 End.X SID/LAN End.X SIDs associated
   with different topologies the node participates in, the SRv6 End.X
   SID sub-TLV as defined in [I-D.bashandy-isis-srv6-extensions] MUST be
   advertised as sub-TLVs in the MT Intermediate Systems TLV (type 222).
   The SR bandwidth sub-TLV as defined in this document SHOULD also be
   carried in the MT Intermediate Systems TLV.

8.  Fast Repair

   In some instances it is desirable to provide some form of fast repair
   for a failed link or node.  The methods available fall into two
   categories, end-to-end, for example 1+1, and IP fast reroute.
   Whichever of these is used, it is desirable that the repair path
   provides the same level of service to the tenant as the tenant's
   normal service.  This would mean that the repair path needs to be
   constrained to the tenant's topology and resource, or to some repair
   topology and resource reserved exclusively for that tenant for the
   duration of the repair.  The normal way that IPFRR operates is that
   the point of local repair (PLR) calculates the repair path based on
   the information flooded by the routing protocol.  How the PLR can
   maintain the level of service through the repair is for further
   study.



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9.  LAN interface

   The use of multi-point to multi-point (MP2MP) interfaces is currently
   out of scope for this design.

   A LAN interface MUST be used in point to point mode.

   Note support for MP2MP may be needed in the future, and this is for
   further study.

10.  Security Considerations

   This document introduces no additional security vulnerabilities to
   IS-IS and OSPF.

   The mechanism proposed in this document is subject to the same
   vulnerabilities as any other protocol that relies on IGPs.

11.  IANA Considerations

   This document requests IANA to allocate a sub-TLV type as defined in
   Section 4 from "Sub-TLVs for TLVs 22, 23, 25, 141, 222 and 223"
   registry.

            Value     Description                      Reference
            -----     --------------------             -------------
            TBA1      SR bandwidth sub-TLV             This document

   Per TLV information where SR bandwidth sub-TLV can be part of:

        TLV  22 23 25 141 222 223
        ---  --------------------
             y  y  n   y   y   y

12.  Acknowledgments

   The authors would like to thank Mach Chen, Robin Li and Dean Cheng
   for the review and discussion of this document.

13.  References

13.1.  Normative References

   [I-D.dong-spring-sr-for-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., and T. Miyasaka, "Segment
              Routing for Enhanced VPN Service", draft-dong-spring-sr-
              for-enhanced-vpn-01 (work in progress), July 2018.




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   [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>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

13.2.  Informative References

   [I-D.bashandy-isis-srv6-extensions]
              Ginsberg, L., Bashandy, A., Filsfils, C., and B. Decraene,
              "IS-IS Extensions to Support Routing over IPv6 Dataplane",
              draft-bashandy-isis-srv6-extensions-01 (work in progress),
              September 2017.

   [I-D.dong-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., and T. Miyasaka, "A
              Framework for Enhanced Virtual Private Networks (VPN+)",
              draft-dong-teas-enhanced-vpn-02 (work in progress),
              October 2018.

   [I-D.filsfils-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-filsfils-spring-srv6-network-
              programming-05 (work in progress), July 2018.

   [I-D.geng-detnet-info-distribution]
              Geng, X. and M. Chen, "IGP-TE Extensions for DetNet
              Information Distribution", draft-geng-detnet-info-
              distribution-01 (work in progress), September 2017.







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   [I-D.ietf-detnet-architecture]
              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", draft-ietf-
              detnet-architecture-04 (work in progress), October 2017.

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
              segment-routing-extensions-15 (work in progress), December
              2017.

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-00 (work in progress), May 2018.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.

   [I-D.ietf-teas-sr-rsvp-coexistence-rec]
              Sitaraman, H., Beeram, V., Minei, I., and S. Sivabalan,
              "Recommendations for RSVP-TE and Segment Routing LSP co-
              existence", draft-ietf-teas-sr-rsvp-coexistence-rec-04
              (work in progress), May 2018.

   [RFC4124]  Le Faucheur, F., Ed., "Protocol Extensions for Support of
              Diffserv-aware MPLS Traffic Engineering", RFC 4124,
              DOI 10.17487/RFC4124, June 2005,
              <https://www.rfc-editor.org/info/rfc4124>.

Authors' Addresses

   Jie Dong
   Huawei Technologies

   Email: jie.dong@huawei.com


   Stewart Bryant
   Huawei Technologies

   Email: stewart.bryant@gmail.com





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