Internet DRAFT - draft-xie-idr-bgpls-sr-vtn-mt

draft-xie-idr-bgpls-sr-vtn-mt







IDR Working Group                                                 C. Xie
Internet-Draft                                                     C. Li
Intended status: Standards Track                           China Telecom
Expires: January 14, 2021                                        J. Dong
                                                                   Z. Li
                                                     Huawei Technologies
                                                           July 13, 2020


 BGP-LS with Multi-topology for Segment Routing based Virtual Transport
                                Networks
                    draft-xie-idr-bgpls-sr-vtn-mt-01

Abstract

   Enhanced VPN (VPN+) as defined in I-D.ietf-teas-enhanced-vpn aims to
   provide enhanced VPN service to support applications's needs of
   enhanced isolation and stringent performance requirements.  VPN+
   requries integration between the overlay VPN and the underlay
   network.  A Virtual Transport Network (VTN) is a virtual network
   which consists of a subset of the network toplogy and network
   resources allocated from the underlay network.  A VTN could be used
   as the underlay for one or a group of VPN+ services.

   I-D.dong-idr-bgpls-sr-enhanced-vpn defines the BGP-LS extensions to
   distribute the information of Segment Routing (SR) based VTNs to
   external entities, such as the network controllers.  This document
   describes a simplified mechanism to distribute the information of SR
   based VTNs using BGP-LS with Multi-Topology.

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
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   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



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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 January 14, 2021.

Copyright Notice

   Copyright (c) 2020 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
   2.  Advertisement of SR VTN Topology  . . . . . . . . . . . . . .   3
     2.1.  Intra-domain Topology Advertisement . . . . . . . . . . .   3
     2.2.  Inter-Domain Topology Advertisement . . . . . . . . . . .   5
   3.  Advertisement of VTN Resource Attribute . . . . . . . . . . .   6
     3.1.  Advertising Topology specific TE attributes . . . . . . .   6
   4.  Scalability Considerations  . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   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
   enhanced isolation and have more stringent performance requirements
   than that can be provided with traditional overlay VPNs.  These
   properties cannot be met with pure overlay networks, as they require
   integration between the underlay and the overlay networks.
   [I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN
   and describes the candidate component technologies in different



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   network planes and layers.  An enhanced VPN can be used for 5G
   transport network slicing, and will also be of use in more generic
   scenarios.

   To meet the requirement of enhanced VPN services, a number of Virtual
   Transport Networks (VTNs) need to 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 VPN+ service or a
   group of VPN+ services.

   [I-D.dong-spring-sr-for-enhanced-vpn] specifies how segment routing
   (SR) [RFC8402] can be used to build virtual transport networks (VTNs)
   with the required network topology and network resources, which could
   be used as the underlay of enhanced VPN services.
   [I-D.dong-lsr-sr-enhanced-vpn] and [I-D.xie-lsr-isis-sr-vtn-mt]
   specifies the IGP mechanism and extensions to build a set of SR based
   VTNs.  When a VTN spans multiple IGP areas or multiple Autonomous
   Systems (ASes), BGP-LS is needed to advertise the VTN information in
   each IGP area or AS to the network controller, so that the controller
   could use the collected information to build the inter-area or inter-
   AS SR VTNs.

   [I-D.dong-idr-bgpls-sr-enhanced-vpn] defines the BGP-LS extensions to
   distribute the information of Segment Routing (SR) based VTNs to
   external entities, such as the network controllers, which allows
   flexible combination of the topology and resource attribute to build
   customized VTNs.  While in some network scenarios, it is assumed that
   each VTN has an independent topology and a set of dedicated network
   resources.  For such scenarios, this document describes a simplified
   mechanism to distribute the information of SR based VTNs using BGP-LS
   with Multi-Topology.

2.  Advertisement of SR VTN Topology

   [I-D.xie-lsr-isis-sr-vtn-mt] describes the ISIS Multi-topology
   mechanisms to distribute the topology attributes of SR based VTNs.
   This section describes the corresponding BGP-LS mechanism to
   distribute both the intra-domain and inter-domain topology attributes
   of SR based VTNs.

2.1.  Intra-domain Topology Advertisement

   In section 3.2.1.5 of [RFC7752], 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.





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   [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 Adj-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
   MT-ID TLV can be carried in the link descriptor to identify the
   corresponding topology of the End.X 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."

   Editor's note: the above rules 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.  Based on the WG's
   opinion, this will be elaborated in a future version.







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2.2.  Inter-Domain Topology Advertisement

   [I-D.ietf-idr-bgpls-segment-routing-epe] and
   [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions for
   advertisement of BGP topology information between ASes and the BGP
   Peering Segment Identifiers.  Such information could be used by a
   network controller for the computation and instantiation of inter-AS
   traffic engineering SR paths.

   In some network scenarios, there are needs to create VTNs which span
   multiple ASes.  The inter-domain VTNs could have different inter-
   domain connectivity, and may be associated with different set of
   network resources in each domain and also on the inter-domain links.
   In order to build the multi-domain VTNs using segment routing, it is
   necessary to advertise the topology and resource attribute of VTN on
   the inter-domain links and the associated BGP Peering SIDs.

   Depending on the requirement of inter-domain VTNs, different
   mechanism can be used on the inter-domain connection:

   o  One EBGP session between two ASes can be established over multiple
      underlying links.  In this case, different underlying links can be
      used for different inter-domain VTNs which requires link isolation
      between each other.  In another similar case, the EBGP session is
      established over a single link, while the network resource (e.g.
      bandwidth) on this link can be partitioned into several pieces,
      each of which can be considered as a virtual member link.  In both
      cases, different BGP Peer-Adj-SIDs SHOULD be allocated to each
      underlying physical or virtual member link, and ASBRs SHOULD
      advertise the VTN identifier associated with each BGP Peer-Adj-
      SID.

   o  For inter-domain connection between two ASes, multiple EBGP
      sessions can be established between different set of peering
      ASBRs.  It is possible that some of these BGP sessions are used
      for one multi-domain VTN, while some other BGP sessions are used
      for another multi-domain VTN.  In this case, different BGP peer-
      node-SIDs are allocated to each BGP session, and ASBRs SHOULD
      advertise the VTN identifier associated with each BGP Peer-node-
      SIDs.

   o  At the AS-level topology, different multi-domain VTNs may have
      different inter-domain connectivity.  Different BGP Peer-Set-SIDs
      can be allocated to represent the groups of BGP peers which can be
      used for load-balancing in each multi-domain VTN.

   When MT-ID is used consistently in multiple ASes covered by a VTN,
   the topology-specific BGP peering SIDs can be advertised with the MT-



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   ID carried in the corresponding Link NLRI.  This can be achieved with
   the existing mechanisms as defined in
   [RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and
   [I-D.ietf-idr-bgpls-srv6-ext].

   In network scenarios where consistent usage of MT-ID among multiple
   ASes can not be expected, then a global-significant VTN ID needs to
   be introduced to define the AS level topologies.  Within each domain,
   the MT based mechanism could be used for intra-domain topology
   advertisement.  The detailed mechanism is specified in
   [I-D.dong-idr-bgpls-sr-enhanced-vpn].

3.  Advertisement of VTN Resource Attribute

   [I-D.xie-lsr-isis-sr-vtn-mt] specifies the mechanism to advertise the
   resource information associated with each VTN.  This section
   describes the corresponding BGP-LS mechanisms.

3.1.  Advertising Topology specific TE attributes

   The information of the network resources associated with a VTN can be
   specified by carrying the Link TE attribute TLVs [RFC7752] in BGP-LS
   Attribute, with the associated MT-ID carried in the corresponding
   Link NLRI.

   When Maximum Link Bandwidth sub-TLV is carried in the MT-ISN TLV, it
   indicates the amount of link bandwidth allocated to the corresponding
   VTN.  The bandwidth allocated to a VTN can be exclusive for services
   carried in the corresponding VTN.  The usage of other TE attribute
   TLVs in topology-specific TLVs is for further study.

4.  Scalability Considerations

   The mechanism described in this document requires that each VTN has
   an independent topology, and for inter-domain VTNs, the MT-ID used in
   each involved domain is consistent.  While this brings the benefits
   of simplicity, it also has some limitations.  For example, it means
   that even if multiple VTNs may have the same topology attribute, they
   would still need to be identified using different MT-IDs in the
   control plane.  This requires that for each VTN, independent path
   computation would be executed.  The number of VTNs supported in a
   network may be dependent on the number of topologies supported, which
   is related to the control plane computation overhead.








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5.  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.

6.  IANA Considerations

   This document does not request any IANA actions.

7.  Acknowledgments

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

8.  References

8.1.  Normative References

   [I-D.dong-spring-sr-for-enhanced-vpn]
              Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., and
              Z. Li, "Segment Routing for Resource Guaranteed Virtual
              Networks", draft-dong-spring-sr-for-enhanced-vpn-08 (work
              in progress), June 2020.

   [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-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-03 (work in progress), July 2020.







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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>.

   [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>.

   [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>.

   [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>.

8.2.  Informative References

   [I-D.dong-idr-bgpls-sr-enhanced-vpn]
              Dong, J., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS
              Extensions for Segment Routing based Enhanced VPN", draft-
              dong-idr-bgpls-sr-enhanced-vpn-02 (work in progress), June
              2020.

   [I-D.dong-lsr-sr-enhanced-vpn]
              Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L.,
              and S. Bryant, "IGP Extensions for Segment Routing based
              Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-04 (work in
              progress), June 2020.

   [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-08
              (work in progress), April 2020.

   [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+)
              Services", draft-ietf-teas-enhanced-vpn-05 (work in
              progress), February 2020.






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   [I-D.xie-lsr-isis-sr-vtn-mt]
              Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi-
              Topology (MT) for Segment Routing based Virtual Transport
              Network", draft-xie-lsr-isis-sr-vtn-mt-00 (work in
              progress), March 2020.

   [RFC8667]  Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
              Extensions for Segment Routing", RFC 8667,
              DOI 10.17487/RFC8667, December 2019,
              <https://www.rfc-editor.org/info/rfc8667>.

Authors' Addresses

   Chongfeng Xie
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing  102209
   China

   Email: xiechf@chinatelecom.cn


   Cong Li
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing  102209
   China

   Email: licong@chinatelecom.cn


   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing  100095
   China

   Email: jie.dong@huawei.com


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

   Email: lizhenbin@huawei.com



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