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Introducing Resource Awareness to SR Segments
draft-ietf-spring-resource-aware-segments-06

Document Type Active Internet-Draft (spring WG)
Authors Jie Dong , Stewart Bryant , Takuya Miyasaka , Yongqing Zhu , Fengwei Qin , Zhenqiang Li , Francois Clad
Last updated 2022-10-11
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draft-ietf-spring-resource-aware-segments-06
SPRING Working Group                                             J. Dong
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                               S. Bryant
Expires: 14 April 2023                              University of Surrey
                                                             T. Miyasaka
                                                        KDDI Corporation
                                                                  Y. Zhu
                                                           China Telecom
                                                                  F. Qin
                                                                   Z. Li
                                                            China Mobile
                                                                 F. Clad
                                                           Cisco Systems
                                                         11 October 2022

             Introducing Resource Awareness to SR Segments
              draft-ietf-spring-resource-aware-segments-06

Abstract

   This document describes the mechanism to associate network resources
   to Segment Routing Identifiers (SIDs).  Such SIDs are referred to as
   resource-aware SIDs in this document.  The resource-aware SIDs retain
   their original forwarding semantics, but with the additional
   semantics to identify the set of network resources available for the
   packet processing and forwarding action.  The resource-aware SIDs can
   therefore be used to build SR paths or virtual networks with a set of
   reserved network resources.  The proposed mechanism is applicable to
   both segment routing with MPLS data plane (SR-MPLS) and segment
   routing with IPv6 data plane (SRv6).

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 14 April 2023.

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Copyright Notice

   Copyright (c) 2022 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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Segments with Resource Awareness  . . . . . . . . . . . . . .   3
     2.1.  SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  SRv6  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Control Plane Considerations  . . . . . . . . . . . . . . . .   7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Segment Routing (SR) [RFC8402] specifies a mechanism to steer packets
   through an ordered list of segments.  A segment is referred to by its
   Segment Identifier (SID).  With SR, explicit source routing can be
   achieved without introducing per-path state into the network.
   Compared with RSVP-TE [RFC3209], the base SR specifications do not
   have the capability of reserving network resources or identifying a
   set of network resources reserved for an individual or a group of
   services or customers.  Although a centralized controller can have a
   global view of network state and can provision different services
   using different SR paths, in data packet forwarding it still relies
   on the DiffServ QoS mechanism [RFC2474] [RFC2475] to provide coarse-
   grained traffic differentiation in the network.  While such a
   mechanism may be sufficient for some types of services, some
   customers or services may require to have a set of dedicated network
   resources allocated in the network to achieve resource isolation from

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   other customers/services in the same network.  Also note the number
   of such customers or services could be larger than the number of
   traffic classes available with DiffServ QoS.

   Without needing to define new SID types, this document extends the SR
   paradigm by associating SIDs with network resource attributes.  These
   resource-aware SIDs retain their original functionality, with the
   additional semantics of identifying the set of network resources
   available for the packet processing action.  Typical types of network
   resources include link bandwidth, buffers, and queues that are
   associated with class of service, scheduling weights or time cycles,
   and it is also possible to associate SR SIDs with other types of
   resources (e.g., the processing and storage resources).  On a
   particular segment, multiple resource-aware SIDs can be allocated,
   each of which represents a subset of network resources allocated in
   the network to meet the requirements of an individual or a group of
   customers or services.  The allocation of network resources on
   segments can be done either via local configuration or via a
   centralized controller.  Other approaches are possible such as use of
   a control plane signaling protocol, but they are out of the scope of
   this document.  Each set of network resources can be associated with
   one or multiple resource-aware SIDs.  The resource-aware SIDs can be
   used to build SR paths with a set of reserved network resources,
   which can be used to carry service traffic which requires dedicated
   network resources along the path.  The resource-aware SIDs can also
   be used to build SR-based virtual networks with the required network
   topology and resource attributes.  The mechanism is applicable to SR
   with both MPLS data plane (SR-MPLS) and IPv6 data plane (SRv6).

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
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Segments with Resource Awareness

   In Segment Routing architecture [RFC8402], several types of segments
   are defined to represent either topological or service instructions.
   A topological segment can be a node segment or an adjacency segment.
   A service segment may be associated with specific service functions
   for service chaining purpose.  This document introduces additional
   resource semantics to these existing types of SIDs, so that the
   resource-aware SIDs can be used to identify not only the topology or
   service functions, but also the set of network resources allocated on
   the segments for packet processing.

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   This section describes the mechanisms of using SR SIDs to identify
   the additional resource information associated with the SR paths or
   virtual networks based on the two SR data plane instantiations: SR-
   MPLS and SRv6.  The mechanisms to identify the forwarding path or
   network topology with SIDs as defined in [RFC8402] can be reused, and
   the control plane can be based on [RFC4915], [RFC5120] and
   [I-D.ietf-lsr-flex-algo].

2.1.  SR-MPLS

   The MPLS instantiation of Segment Routing is specified in [RFC8660].
   As specified in [RFC8402], an IGP Adjacency Segment (Adj-SID) is an
   SR segment attached to a unidirectional adjacency or a set of
   unidirectional adjacencies.  An IGP Prefix Segment (Prefix-SID) is an
   SR segment attached to an IGP prefix, which identifies an instruction
   to forward the packet along the path computed using the routing
   algorithm in the associated topology.  An IGP node segment is an IGP-
   Prefix segment that identifies a specific router (e.g., a loopback).
   As described in [RFC9086] and [RFC9087], a BGP PeerAdj SID is used as
   an instruction to steer over a local interface towards a specific
   peer node in a peering Autonomous System (AS).  These types of SID
   can be extended to represent both the topological instructions and
   the set of network resources allocated for packet processing
   following the instruction.

   A resource-aware Adj-SID represents a subset of the resources (e.g.,
   bandwidth, buffer and queuing resources) of a given link, thus each
   resource-aware Adj-SID is associated with a subset of the link's
   traffic engineering (TE) capabilities and resources (known as TE
   attributes [RFC2702]).

   For one IGP link, multiple resource-aware Adj-SIDs can be allocated,
   each of which is associated with a subset of the link resources
   allocated on the link.  For one inter-domain link, multiple BGP
   PeerAdj SIDs may be allocated, each of which is associated with a
   subset of the link resources allocated on the inter-domain link.  The
   resource-aware Adj-SIDs may be associated with a specific network
   topology and/or algorithm, so that it is used only for resource-aware
   SR paths computed within the topology and/or algorithm.

   Note this per-segment resource allocation complies with the SR
   paradigm, which avoids introducing per-path state into the network.
   Several approaches can be used to partition and reserve the link
   resources, such as [FLEXE], Layer-2 logical sub-interfaces, dedicated
   queues, etc.  The detailed mechanism of link resource partitioning is
   out of scope of this document.

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   A resource-aware Prefix-SID is associated with a network topology
   and/or algorithm in which the attached node participates, and in
   addition, a resource-aware prefix-SID is associated with a set of
   network resources (e.g., bandwidth, buffer and queuing resources)
   allocated on each node and link participating in the same topology
   and/or algorithm.  Such set of network resources can be used for
   forwarding packets which are encapsulated with this resource-aware
   prefix-SID along the paths computed in the associated topology and/or
   algorithm.

   Although it is possible that each resource-aware prefix-SID is
   associated with a set of dedicated resources in the network, this
   implies the overhead with per-prefix resource reservation in both
   control plane signaling and data plane states, and if network
   resources are allocated for one prefix on all the possible paths, it
   is likely some resources will be wasted.  A practical approach is
   that a common set of network resources are allocated by each network
   node and link participating in a topology and/or algorithm, and are
   associated with a group of resource-aware prefix-SIDs of the same
   topology and/or algorithm.  Such common set of network resources
   constitutes a network resource group.  For a given <topology,
   algorithm> tuple, there can be one or multiple network resource
   groups, the resource-aware prefix-SIDs which are associated with the
   same <topology, algorithm> tuple share the path computation result.

   This helps to reduce the dynamics in per-prefix resource allocation
   and adjustment, so that the network resource can be allocated based
   on planning and does not have to rely on dynamic signaling.  When the
   set of nodes and links participate in a <topology, algorithm> tuple
   changes, the set of network resources allocated on specific nodes and
   links may need to be adjusted.  This means that the resources
   allocated to resource-aware Adj-SIDs on those links may have to be
   adjusted and new TE attributes for the associated Adj-SIDs re-
   advertised.

   For one IGP prefix, multiple resource-aware prefix-SIDs can be
   allocated.  Each resource-aware prefix-SID may be associated with a
   unique <topology, algorithm> tuple, in this case different <topology,
   algorithm> tuples can be used to distinguish the resource-aware
   prefix-SIDs of the same prefix.  In another case, for one IGP prefix,
   multiple resource-aware prefix-SIDs may be associated with the same
   <topology, algorithm> tuple, then an additional control plane
   distinguisher needs to be introduced to distinguish different
   resource-aware prefix-SIDs associated with the same <topology,
   algorithm> but different groups of network resources.

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   A group of resource-aware Adj-SID and resource-aware Prefix-SIDs can
   be used to construct the SID lists, which are used to steer the
   traffic to be forwarded along the explicit paths (either strict or
   loose) and processed using the set of network resources identified by
   the resource-aware SIDs.

   In data packet forwarding, each resource-aware Adj-SID identifies
   both the next-hop and the set of resources used for packet processing
   on the outgoing interface.  Each resource-aware Prefix-SID identifies
   the path to the node which the prefix is attached to, and the common
   set of network resources used for packet forwarding on network nodes
   along the path.  The transit nodes use the resource-aware prefix-SIDs
   to determine the next-hop of the packet and the set of associated
   local resources, then forward the packet to the next-hop using the
   set of local resources.

   When the set of network resources allocated on the egress node also
   needs to be determined, it is RECOMMENDED that Penultimate Hop
   Popping (PHP) [RFC3031] be disabled, otherwise the inner service
   label needs to be used to infer the set of resources to be used for
   packet processing on the egress node of the SR path.

   This mechanism requires the allocation of additional prefix-SIDs or
   adj-SIDs for network segments to identify different sets of network
   resources.  As the number of resource groups increases, the number of
   SIDs would increase accordingly, while it should be noted that there
   is still no per-path state introduced into the network.

2.2.  SRv6

   As specified in [RFC8986], an SRv6 Segment Identifier (SID) is a
   128-bit value which consists of a locator (LOC) and a function
   (FUNCT), optionally it may also contain additional arguments (ARG)
   immediately after the FUNCT.  The Locator part of the SID is routable
   and leads to the node which instantiates that SID, which means the
   Locator can be parsed by all nodes in the network.  The FUNCT part of
   the SID is an opaque identification of a local function bound to the
   SID, and the ARG bits of the SID can be used to encode additional
   information for the processing of the behavior bound to the SID.
   Thus the FUNCT and ARG parts can only be parsed by the node which
   instantiates the SRv6 SID.

   For one SRv6 node, multiple resource-aware SRv6 LOCs can be
   allocated.  A resource-aware LOC is associated with a network
   topology and/or algorithm in which the node participates, and in
   addition, a resource-aware LOC is associated with a set of local
   resources (e.g., bandwidth, buffer, and queueing resources) on each
   node participating in the same topology and/or algorithm.  Such a set

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   of network resources are used to forward the packets with SIDs which
   have the resource-aware LOC as its prefix, along the path computed
   with the associated topology and/or algorithm.  Similar to the
   resource-aware prefix-SIDs in SR-MPLS, a practical approach is that a
   common set of network resources are allocated by each network node
   and link participating in a topology and/or algorithm, and are
   associated with a group of resource-aware LOCs of the same topology
   and/or algorithm.

   For one IGP link, multiple resource-aware SRv6 End.X SIDs can be
   allocated to identify different set of link resources.  Each
   resource-aware End.X SID SHOULD use a resource-aware LOC as its
   prefix.  SRv6 SIDs for other types of functions MAY also be assigned
   as resource-aware SIDs, which can identify the set of network
   resources allocated by the node for executing the behavior.

   A group of resource-aware SRv6 SIDs can be used to construct the SID
   lists, which are used to steer the traffic to be forwarded along the
   explicit paths (either strict or loose) and processed using the set
   of network resources identified by the resource-aware SIDs and
   Locators.

   In data packet forwarding, each resource-aware End.X SID identifies
   both the next-hop and the set of resources used for packet processing
   on the outgoing interface.  Each resource-aware Locator identifies
   the path to the node which the Locator is assigned to, and the set of
   network resources used for packet forwarding on network nodes along
   the path.  The transit nodes use the resource-aware Locators to
   determine the next-hop of the packet and the set of associated local
   resources, then forward the packet to the next-hop using the set of
   local resources.

   This mechanism requires the allocation of additional SRv6 Locators
   and SIDs for network segments to identify different set of network
   resources.  As the number of resource groups increases, the number of
   SRv6 Locators and SIDs would increase accordingly, while it should be
   noted that there is still no per-path state introduced into the
   network.

3.  Control Plane Considerations

   The mechanism described in this document makes use of a centralized
   controller to collect the information about the network
   (configuration, state, routing databases, etc.) as well as the
   service information (traffic matrix, performance statistics, etc.)
   for the planning of network resources based on the service
   requirement.  Then the centralized controller instructs the network
   nodes to allocate the network resources and associate the resources

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   with the resource-aware SIDs.  The resource-aware SIDs can be either
   explicitly provisioned by the controller, or dynamically allocated by
   network nodes then reported to the controller.  The controller is
   also responsible for the centralized computation and optimization of
   the SR paths taking the topology, algorithm and network resource
   constraints into consideration.  The interaction between the
   controller and the network nodes can be based on Netconf/YANG
   [RFC6241] [RFC7950], BGP-LS [RFC7752], BGP SR Policy
   [I-D.ietf-idr-segment-routing-te-policy] or PCEP [RFC5440].  In some
   scenarios, extensions to some of these protocols are needed, which
   are out of the scope of this document.  In some cases, a centralized
   controller may not be used, but this would complicate the operations
   and planning therefore is not suggested.

   On network nodes, the support for a resource group and the
   information to associate packets with that resource group needs to be
   advertised in the control plane, so that all the nodes have a
   consistent view of the resource group.  Given that resource
   management is a central function, the knowledge of the exact
   resources provided to a resource group needs to be known accurately
   by the relevant central control components (e.g., PCE) and the
   network nodes.  This may be done by configuration, alternative
   protocols, or by advertisements in the IGP for collection by BGP-LS.
   If there are related link advertisements, then consistency MUST be
   assured across that set of advertisements.  To advertise its support
   for a given resource group, a node needs to advertise the identifier
   of the resource group, the associated topology and algorithm, the
   resource-aware SIDs and potentially a set of TE attributes
   representing the resources allocated to it.

   The distributed control plane is complementary to the centralized
   controller.  A distributed control plane can be used for the
   collection and distribution of the network topology and resource
   information associated with the resource-aware SIDs among network
   nodes, then some of the nodes can distribute the collected
   information to the centralized controller.  Distributed route
   computation for services with topology and/or resource constraints
   may also be performed by network nodes.  The distributed control
   plane may be based on [RFC4915], [RFC5120], [I-D.ietf-lsr-flex-algo]
   with necessary extensions.

   When a network node is instructed to associate a SID with specific
   resources, its actions will depend on the operational configuration
   of the network.  In some cases the association between SIDs and
   resources is configured on the individual network nodes, and the
   control plane (the IGPs) is used to distribute the information and
   resource availability to the controller and the ingress nodes for TE
   constraint-based path computation.  In hybrid cases with SR and other

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   TE mechanisms co-existing in the network, the IGP advertisements of
   available resources will need to be updated to indicate that there
   has been a change to the available resources resulting from the
   instantiation of a new SID: such updates would be rate-limited in the
   normal way.  In still other cases the association between SIDs and
   network resources is known by the central controller which is
   responsible for all TE management, and the control plane does not
   need to take any additional action.

4.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

5.  Security Considerations

   The security considerations of segment routing in [RFC8402] [RFC8754]
   are applicable to this document.

   The resource-aware SIDs may be used for provisioning of SR paths or
   virtual networks to carry traffic with latency as one of the SLA
   parameters.  By disrupting the latency of such traffic an attack can
   be directly targeted at the customer application, or can be targeted
   at the network operator by causing them to violate their SLA,
   triggering commercial consequences.  Dynamic attacks of this sort are
   not something that networks have traditionally guarded against, and
   networking techniques need to be developed to defend against this
   type of attack.  By rigorously policing ingress traffic and carefully
   provisioning the resources provided to such services, this type of
   attack can be prevented.  However care needs to be taken when
   providing shared resources, and when the network needs to be
   reconfigured as part of ongoing maintenance or in response to a
   failure.

   The details of the underlay network MUST NOT be exposed to third
   parties, to prevent attacks aimed at exploiting shared network
   resources.

6.  Contributors

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   Zhenbin Li
   Email: lizhenbin@huawei.com

   Zhibo Hu
   Email: huzhibo@huawei.com

   Joel Halpern
   Email: jmh@joelhalpern.com

7.  Acknowledgements

   The authors would like to thank Mach Chen, Stefano Previdi, Charlie
   Perkins, Bruno Decraene, Loa Andersson, Alexander Vainshtein and John
   Drake for the valuable discussion and suggestions to this document.

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>.

   [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>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

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   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

8.2.  Informative References

   [FLEXE]    "Flex Ethernet Implementation Agreement", March 2016,
              <http://www.oiforum.com/wp-content/uploads/OIF-FLEXE-
              01.0.pdf>.

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
              Jain, D., and S. Lin, "Advertising Segment Routing
              Policies in BGP", Work in Progress, Internet-Draft, draft-
              ietf-idr-segment-routing-te-policy-20, 27 July 2022,
              <https://www.ietf.org/archive/id/draft-ietf-idr-segment-
              routing-te-policy-20.txt>.

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", Work in Progress,
              Internet-Draft, draft-ietf-lsr-flex-algo-25, 6 October
              2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
              flex-algo-25.txt>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
              <https://www.rfc-editor.org/info/rfc2475>.

   [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>.

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   [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>.

   [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>.

   [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>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC9086]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
              Ray, S., and J. Dong, "Border Gateway Protocol - Link
              State (BGP-LS) Extensions for Segment Routing BGP Egress
              Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
              2021, <https://www.rfc-editor.org/info/rfc9086>.

   [RFC9087]  Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
              and D. Afanasiev, "Segment Routing Centralized BGP Egress
              Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
              2021, <https://www.rfc-editor.org/info/rfc9087>.

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Authors' Addresses

   Jie Dong
   Huawei Technologies
   Email: jie.dong@huawei.com

   Stewart Bryant
   University of Surrey
   Email: stewart.bryant@gmail.com

   Takuya Miyasaka
   KDDI Corporation
   Email: ta-miyasaka@kddi.com

   Yongqing Zhu
   China Telecom
   Email: zhuyq8@chinatelecom.cn

   Fengwei Qin
   China Mobile
   Email: qinfengwei@chinamobile.com

   Zhenqiang Li
   China Mobile
   Email: li_zhenqiang@hotmail.com

   Francois Clad
   Cisco Systems
   Email: fclad@cisco.com

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