Internet DRAFT - draft-xie-lsr-isis-sr-vtn-mt

draft-xie-lsr-isis-sr-vtn-mt







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


   Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual
                           Transport Network
                    draft-xie-lsr-isis-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 some application's needs of
   enhanced isolation and stringent performance requirements.  VPN+
   requires 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 topology 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-lsr-sr-enhanced-vpn defines the IGP extensions to build a
   set of Segment Routing (SR) based VTNs.  This document describes a
   simplified mechanism to build the SR based VTNs using IGP multi-
   topology together with other well-defined IS-IS extensions.

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
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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
   publication of this document.  Please review these documents
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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 Attribute  . . . . . . . . .   3
   3.  Advertisement of SR VTN Resource Attribute  . . . . . . . . .   4
     3.1.  Advertising Topology-specific TE attributes . . . . . . .   4
   4.  Scalability Considerations  . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

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
   network planes and layers.  An enhanced VPN may be used for 5G




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   transport network slicing, and will also be of use in other generic
   scenarios.

   To meet the requirement of enhanced VPN services, a number of virtual
   transport networks (VTN) 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.  Another existing approach is to build a set
   of point-to-point paths, each with a set of network resource reserved
   along the path, such paths is called Virtual Transport Path (VTP).
   Although using a set of dedicated VTPs can provide similar
   characteristics, it has some scalability issues in large networks.

   [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 resource attributes to
   support enhanced VPN services.  With segment routing based data
   plane, Segment Identifiers (SIDs) can be used to represent the
   topology and the set of network resources allocated by network nodes
   to a virtual network.  The SIDs of each VTN and the associated
   topology and resource attributes need to be distributed using control
   plane.

   [I-D.dong-lsr-sr-enhanced-vpn] defines the IGP mechanisms with
   necessary extensions to build a set of Segment Routing (SR) based
   VTNs.  The VTNs could be used as the underlay of the enhanced VPN
   service.  The mechanism described in [I-D.dong-lsr-sr-enhanced-vpn]
   allows flexible combination of the topology and resource attribute to
   build customized VTNs.  In some network scenarios, it is assumed that
   each VTN has an independent topology and a set of dedicated network
   resources.  This document describes a simplified mechanism to build
   the SR based VTNs in those scenarios.

   The approach is to use IS-IS Multi-Topology [RFC5120] with segment
   routing [RFC8667] to define the independent network topologies of
   each VTN.  The information of network resources allocated to a VTN
   can be advertised by using IS-IS MT with the Traffic Engineering (TE)
   extensions defined in [RFC5305].

2.  Advertisement of SR VTN Topology Attribute

   Multi-Topology Routing (MTR) [RFC5120] has been defined to create
   independent topologies in one network.  It also has the capability of
   specifying the customized attributes of each topology.  MTR can be
   used with segment routing based data plane.  The IS-IS extensions to
   support the advertisement of topology-specific MPLS SIDs are
   specified in [RFC8667].  Topology-specific Prefix-SIDs are advertised
   by carrying the Prefix-SID sub-TLVs in the IS-IS TLV 235 (MT IP



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   Reachability) and TLV 237 (MT IPv6 IP Reachability).  Topology-
   specific Adj-SIDs are advertised by carrying the Adj-SID sub-TLVs in
   IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS Neighbor Attribute).

   The IS-IS extensions to support the advertisement of topology-
   specific SRv6 Locators and SIDs are specified in
   [I-D.ietf-lsr-isis-srv6-extensions].  The topology-specific SRv6
   locators are advertised using SRv6 Locator TLV, and SRv6 End SIDs
   inherit the MT-ID from the parent locator.  The topology-specific
   End.X SID are advertised by carrying SRv6 End.X SID sub-TLVs in the
   IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS Neighbor Attribute).

   When each VTN has an independent network topology, the MT-ID could be
   used as the identifier of VTN in control plane.  Thus the topology
   attribute of a VTN could be advertised using MTR with segment
   routing.

3.  Advertisement of SR VTN Resource Attribute

   In order to perform constraint based path computation for each VTN on
   the network controller or on the ingress nodes, the network resource
   attribute associated with each VTN needs to be advertised.

3.1.  Advertising Topology-specific TE attributes

   On each network link, the information of the network resources
   associated with a VTN can be specified by carrying the TE attributes
   sub-TLVs [RFC5305] in the IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS
   Neighbor Attribute) of the corresponding topology.

   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 attributes
   in topology-specific TLVs is for further study.

   Editor's note1: It is noted that carrying per-topology TE attributes
   was considered as a possible feature in future when the encoding of
   IS-IS multi-topology was defined [RFC5120].

4.  Scalability Considerations

   The mechanism described in this document requires that each VTN has
   an independent topology.  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




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   VTNs supported in a network may be dependent on the control plane
   computation overhead.

5.  Security Considerations

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

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

6.  IANA Considerations

   This document does not request any IANA actions.

7.  Acknowledgments

   The authors would like to thank Zhibo Hu, Dean Cheng, Les Ginsberg
   and Peter Psenak 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-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.

   [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>.

   [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>.





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   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [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>.

   [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>.

8.2.  Informative References

   [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-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-16 (work in
              progress), June 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.

Authors' Addresses

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

   Email: xiechf@chinatelecom.cn







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   Chenhao Ma
   China Telecom
   China Telecom Beijing Information Science & Technology, Beiqijia
   Beijing  102209
   China

   Email: machh@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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