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Versions: 00

IDR Working Group                                                J. Dong
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: May 7, 2020                                    November 4, 2019


        BGP-LS Extensions for Segment Routing based Enhanced VPN
                draft-dong-idr-bgpls-sr-enhanced-vpn-00

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 be used for 5G transport network slicing, and will also be of
   use in more generic scenarios.  This document specifies BGP-LS based
   mechanism with necessary extensions to advertise the information of
   Segment Routing (SR) based virtual networks.  These virtual networks
   could be used as the underlay of enhanced VPN service.  The proposed
   mechanism is applicable to both segment routing with MPLS data plane
   (SR-MPLS) and segment routing with IPv6 data plane (SRv6).

Requirements Language

   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].

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 May 7, 2020.





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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
   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.  Advertisement of Transport Network Slice Definition . . . . .   3
     2.1.  Sub-TLVs of TNSD TLV  . . . . . . . . . . . . . . . . . .   4
   3.  Advertisement of Network Topology and Resource Attributes . .   6
     3.1.  Intra-domain Network Topology Advertisement . . . . . . .   6
       3.1.1.  MTR based Topology Advertisement  . . . . . . . . . .   6
       3.1.2.  Flex-Algo based Topology Advertisement  . . . . . . .   7
     3.2.  Intra-domain Resource Information Advertisement . . . . .   8
     3.3.  Inter-Domain Topology and Resource Information
           Advertisement . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Driven largely by needs arising from the 5G mobile network, the
   concept of network slicing has gained traction
   [NGMN-NS-Concept][TS23501][TS28530] . Network slicing requires to
   partition the physical network to several pieces to provide each
   network slice with the required networking, computing, and storage
   resources and functions to meet the requirement of slice tenants.  As
   specified in [I-D.ietf-teas-enhanced-vpn], a transport network slice
   is a virtual (logical) network with a particular network topology and
   a set of shared or dedicated network resources, which are used to
   provide the network slice consumer with the required connectivity,
   appropriate isolation and specific Service Level Agreement (SLA).



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   The enhanced VPN service (VPN+) [I-D.ietf-teas-enhanced-vpn] is
   targeted at new applications which require better isolation from both
   control plane and data plane's perspective and have more stringent
   performance requirements than can be provided with existing overlay
   VPNs.  To meet the requirement of enhance VPN services, a number of
   virtual networks need be created, each with a subset of the underlay
   network topology and a set of network resources allocated to meet the
   requirement of a specific enhanced VPN or a group of enhanced VPNs.
   In the context of 5G, each virtual network can be considered as a
   transport network slice.

   [I-D.dong-spring-sr-for-enhanced-vpn] describes the mechanisms to
   build Segment Routing (SR) based virtual networks, which could be
   used to as the underlay of different enhanced VPN services.
   [I-D.dong-lsr-sr-enhanced-vpn] specifies the IGP mechanism and
   extensions to build a set of SR based virtual networks with
   customized topology and resource attributes.  When the virtual
   networks span multiple areas or multiple Autonomous Systems(ASes),
   BGP-LS is needed to advertise the virtual network information of each
   IGP area or AS to the network controller to build the inter-area or
   inter-AS SR based transport network slices.

   This document describes BGP-LS [RFC7752] based mechanism with
   necessary extensions to advertise the topology and resource
   information of intra-domain and inter-domain Segment Routing (SR)
   based transport network slices.  The definition of transport network
   slice is advertised as a node attribute using BGP-LS.  The attributes
   of network resources allocated to a transport network slice is
   advertised as a link attribute using BGP-LS.

2.  Advertisement of Transport Network Slice Definition

   The definition of a transport network slice or virtual network
   consists of the combination of a set of network attributes.  The
   topology attribute and resource attribute are two major types of
   attributes of a transport network slice, and they can be decoupled in
   the control plane advertisement and processing.  Transport Network
   Slice Definition (TNSD) TLV is a new TLV of the optional BGP-LS
   Attribute which is associated with the node NLRI.

   The format of TNSD TLV is as follows:










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      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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Flags            |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Transport Network Slice Identifier              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Sub-TLVs                             |
      ~                            ...                                ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   o  Type: TBD

   o  Length: the length of the value field of the sub-TLV.  It is
      variable dependent on the included Sub-TLVs.

   o  Flags: 16-bit flags to indicate the attributes of the transport
      network slice.  All flags are reserved and MUST be set to zero on
      transmission and ignored on reception.

   o  Reserved: this field is reserved for future use, MUST be set to
      zero on transmission and ignored on reception.

   o  Transport Network Slice Identifier (TNSI): A 32-bit identifier
      which is used to identify a transport network slice.

   o  Sub-TLVs: optional sub-TLVs to specify the attributes of a virtual
      network.

2.1.  Sub-TLVs of TNSD TLV

   The sub-TLVs of the TNSD TLV is used to advertise the identifiers of
   different types of attributes of the transport network slice.  Two
   sub-TLVs of the TNSD TLV are defined in this document: Network
   Topology sub-TLV and Network Resource sub-TLV.

   The format of the Network Topology sub-TLV is as below:









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      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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |M|A|          Flags            |             MT-ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Algorithm   |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   o  Type: 1

   o  Length: the length of the value field of the sub-TLV.

   o  Flags: 16-bit flags to indicate the attribute of the virtual
      network topology.  Where:

         M flag: indicates the topology is determined by the MT-ID when
         set.

         A flag: indicates the topology is determined by the Algorithm
         when set.  In this case, the value of the Algorithm field
         SHOULD be between 128 and 255.

   o  MT-ID: 16-bit identifier which indicates the multi-topology
      identifier of the IGP topology.

   o  Algorithm: 8-bit identifier which indicates the algorithm which is
      used within this network topology.

   o  Reserved: this field is reserved for future use, MUST be set to
      zero on transmission and ignored on reception.

   The format of the Network Resource sub-TLV is as below:

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Flags            |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Resource Identifier                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:



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      Type: 2

      Length: 6 octets.

      Flags: 16 bit flags.  All the bits are reserved, which MUST be set
      to 0 on transmission and ignored on receipt.

      Reserved: this field is reserved for future use, MUST be set to
      zero on transmission and ignored on reception.

      Resource Identifier: A 32-bit identifier which is used to identify
      the group of network resources allocated to a transport network
      slice.

3.  Advertisement of Network Topology and Resource Attributes

   [I-D.dong-lsr-sr-enhanced-vpn] describes the candidate IGP mechanisms
   to distribute the topology attributes of SR based transport network
   slices.  This section describes the BGP-LS mechanism to distribute
   both the intra-domain and inter-domain topology and resource
   attribute of SR based transport network slices.

3.1.  Intra-domain Network Topology Advertisement

3.1.1.  MTR based Topology Advertisement

   In section 3.2.1.5 of [RFC7752], the Multi-Topology Identifier (MT-
   ID) TLV is defined, which can contain one or more IS-IS or OSPF
   Multi-Topology IDs.  The MT-ID TLV MAY be present in a Link
   Descriptor, a Prefix Descriptor, or the BGP-LS attribute of a Node
   NLRI.

   [I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS
   extensions to carry the segment routing information using TLVs of
   BGP-LS Attribute.  When MTR is used with SR-MPLS data plane,
   topology-specific prefix SIDs and topology-specific adjacency SIDs
   can be carried in the BGP-LS Attribute associated with the prefix
   NLRI and link NLRI respectively, the MT-ID TLV is carried in the
   prefix descriptor and link descriptor to identify the corresponding
   topology of the SIDs.

   [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to
   advertise SRv6 segments along with their functions and attributes.
   When MTR is used with SRv6 data plane, the SRv6 Locator TLV is
   carried in the BGP-LS Attribute associated with the prefix-NLRI, the
   MT-ID TLV can be carried in the prefix descriptor to identify the
   corresponding topology of the SRv6 Locator.  The SRv6 End.X SIDs are
   carried in the BGP-LS Attribute associated with the link NLRI, the



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   MT-ID TLV can be carried in the link descriptor to identify the
   corresponding topology of the SIDs.  The SRv6 SID NLRI is defined to
   advertise other types of SRv6 SIDs, in which the SRv6 SID Descriptors
   can include the MT-ID TLV so as to advertise topology-specific SRv6
   SIDs.

   [RFC7752] also defines the rules of the usage of MT-ID TLV:

   "In a Link or Prefix Descriptor, only a single MT-ID TLV containing
   the MT-ID of the topology where the link or the prefix is reachable
   is allowed.  In case one wants to advertise multiple topologies for a
   given Link Descriptor or Prefix Descriptor, multiple NLRIs need to be
   generated where each NLRI contains an unique MT-ID.  In the BGP-LS
   attribute of a Node NLRI, one MT-ID TLV containing the array of MT-
   IDs of all topologies where the node is reachable is allowed."

   This indicates that only one MT-ID is allowed to be carried the Link
   or Prefix descriptors.  When a link or prefix participates in
   multiple topologies, multiple NLRIs needs to be generated to report
   all the topologies a link or prefix participates in, together with
   the topology-specific segment routing information.  This would
   increase the number of BGP Updates and may introduce additional
   processing burden to both the sending BGP speaker and the receiving
   network controller.  When the number of topologies in a network is
   not a small number, some optimization may be introduced for the
   reporting of multi-topology information and the associated segment
   routing information in BGP-LS.  This will be elaborated in a future
   version.

3.1.2.  Flex-Algo based Topology Advertisement

   As specified in [I-D.dong-lsr-sr-enhanced-vpn], Flex-Algo
   [I-D.ietf-lsr-flex-algo] can also be used to advertise the
   topological constraints of a virtual network.  The BGP-LS extensions
   for SR-MPLS [I-D.ietf-idr-bgp-ls-segment-routing-ext] and SRv6
   [I-D.ietf-idr-bgpls-srv6-ext]provide the mechanisms to advertise the
   Flex-Algo definition information and the algorithm-specific segment
   routing information.

   The Flex-Algo definition can be used to describe the topological
   constraints for path computation.  According to the network nodes'
   participation of a Flex-Algo, and the rules of including or excluding
   specific Admin Groups (colors), a network topology can be determined
   by a Flex-Algo.

   In[I-D.ietf-idr-bgp-ls-segment-routing-ext], algorithm-specific
   prefix-SIDs can be advertised as Link attributes of the associated
   Link NLRI.  In [I-D.ietf-idr-bgpls-srv6-ext], algorithm-specific SRv6



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   Locators can be advertised as Link attributes of the associated
   prefix NLRI, and algorithm-specific End.X SIDs can be advertised as
   Link attributes of the associated Link NLRI.  Other types of SRv6
   SIDs are advertised using SRv6 SID NLRI and can also be algorithm-
   specific.

3.2.  Intra-domain Resource Information Advertisement

   [I-D.dong-lsr-sr-enhanced-vpn] specifies the mechanism to advertise
   the resource information associated with each transport network
   slice.  It is based on the extensions to the advertisement of L2
   bundle member links information.  This section defines the
   corresponding BGP-LS extensions.

   In [I-D.ietf-idr-bgp-ls-segment-routing-ext], L2 bundle member
   Attribute TLV is used to advertise the attributes of a member link of
   a parent L3 link.  Two new sub-TLVs are defined under the L2 bundle
   member Attribute TLV.

   The link attribute sub-TLV is use to carry the link characteristics
   of a L2 member link.  The format of the sub-TLV is as below:

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Flags             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

      Type: TBD

      Length: 4 octets.

      Flags: 16-bit flags.  This field is consistent with the Flag field
      in IS-IS Link Attribute sub-TLV in [RFC5029].  In addition to the
      flags defined in [RFC5029], A new Flag V is defined in this
      document.  When the V flag is set, it indicates this link is a L2
      virtual member link.

   The Resource Identifier (ResID) sub-TLV is used to describe to which
   resource group a particular member links belongs to.

   A global-significant Resource Identifier (ResID) is introduced to
   identify a resource group which is the collection of all the network
   resources allocated to a transport network slice.



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   The format of Resource Identifier sub-TLV is as below:

       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             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Flags            |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Resource Identifier                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   o  Type: TBD

   o  Length: 12 octets.

   o  Flags: 16 bit flags.  All the bits are reserved, which MUST be set
      to 0 on transmission and ignored on receipt.

   o  Reserved: this field is reserved for future use.  MUST be set to 0
      on transmission and ignored on receipt.

   o  Bundle Member Link Local Identifier: A 32-bit local identifier of
      a member link.  The link can be physical or virtual.

   o  Resource Identifier: A 32-bit global-significant identifier to
      identify the resource group this member link belongs to.

3.3.  Inter-Domain Topology and Resource Information Advertisement

   [I-D.ietf-idr-bgpls-segment-routing-epe] defines the BGP-LS
   extensions for advertisement of BGP Peering Segments and the peering
   topology information between ASes.  Such information could be used by
   a network controller for the computation and instantiation of inter-
   AS traffic engineering SR paths.

   In some scenarios, transport network slices which spans multiple ASes
   need to be created.  The inter-domain network slices may have
   different inter-domain connectivity, and may be associated with
   different set of network resources in each domain and on the inter-
   domain links.  In order to build the inter-domain transport network
   slices using segment routing, it is necessary to advertise the
   topology and resource attribute of the inter-domain links and the
   associated BGP Peering Segments.





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   Depending on the requirement of inter-domain network slices,
   different levels of isolation on the inter-domain connection can be
   achieved:

   o  One EBGP session between two ASes can be established over several
      underlying links.  In this case, different underlying links can be
      used for different inter-domain transport network slices which
      requires hard isolation between each other.  In another similar
      case, the EBGP session is established over a single link, while
      the resource on this link can be splited into several pieces, each
      of which can be considered as a virtual member link.  In both
      cases, different BGP Peer-Adj-SIDs are allocated to each
      underlying physical or virtual link, and the ASBRs SHOULD
      advertise the transport network slice identifiers associated with
      each BGP Peer-Adj-SID.

   o  For inter-domain connection between two ASes, multiple EBGP
      sessions can be established between different peering ASBRs.  It
      is possible that some of these BGP sessions are used for one
      inter-domain transport network slice, while some other BGP
      sessions are used for another inter-domain transport network
      slice.  Different BGP peer-node-SIDs are allocated to each BGP
      session, and ASBR SHOULD advertise the information of topology
      identifiers associated with different BGP Peer-node-SIDs.

   o  Different inter-domain transport network slices can have different
      inter-domain connectivity at the AS level.  Different BGP Peer-
      Set-SID can be allocated to represent the groups of BGP peers
      which can be used for load-balancing in each transport network
      slice.

   The detailed protocol extensions for advertising the inter-domain
   network slice information will be specified in a future version.

4.  Security Considerations

   This document introduces no additional security vulnerabilities to
   BGP-LS.

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

5.  IANA Considerations

   TBD






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6.  Acknowledgments

   The authors would like to thank Shunwan Zhuang for the review and
   discussion of this document.

7.  References

7.1.  Normative References

   [I-D.dong-lsr-sr-enhanced-vpn]
              Dong, J. and S. Bryant, "IGP Extensions for Segment
              Routing based Enhanced VPN", draft-dong-lsr-sr-enhanced-
              vpn-01 (work in progress), October 2018.

   [I-D.dong-spring-sr-for-enhanced-vpn]
              Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., and
              Z. Li, "Segment Routing for Enhanced VPN Service", draft-
              dong-spring-sr-for-enhanced-vpn-05 (work in progress),
              October 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-segment-routing-epe]
              Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
              S., and J. Dong, "BGP-LS extensions for Segment Routing
              BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
              segment-routing-epe-19 (work in progress), May 2019.

   [I-D.ietf-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Service", draft-ietf-teas-enhanced-vpn-03 (work in
              progress), September 2019.

   [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>.

   [RFC5029]  Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
              Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
              September 2007, <https://www.rfc-editor.org/info/rfc5029>.





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   [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>.

7.2.  Informative References

   [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-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-04 (work in progress), September 2019.

   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extension to Support Segment Routing over
              IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-03
              (work in progress), October 2019.

   [NGMN-NS-Concept]
              "NGMN NS Concept", 2016, <https://www.ngmn.org/fileadmin/u
              ser_upload/161010_NGMN_Network_Slicing_framework_v1.0.8.pd
              f>.

   [TS23501]  "3GPP TS23.501", 2016,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3144>.

   [TS28530]  "3GPP TS28.530", 2016,
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3273>.

Authors' Addresses

   Jie Dong
   Huawei Technologies

   Email: jie.dong@huawei.com







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   Zhibo Hu
   Huawei Technologies

   Email: huzhibo@huawei.com















































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