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L                                                              P. Shaofu
Internet-Draft                                                    C. Ran
Intended status: Standards Track                         ZTE Corporation
Expires: May 30, 2020                                          G. Mirsky
                                                               ZTE Corp.
                                                       November 27, 2019


        IGP Flexible Algorithm Optimazition for Netwrok Slicing
                draft-peng-lsr-flex-algo-opt-slicing-00

Abstract

   IGP Flex Algorithm proposes a solution that allows IGPs themselves to
   compute constraint based paths over the network, and it also
   specifies a way of using Segment Routing (SR) Prefix-SIDs and SRv6
   locators to steer packets along the constraint-based paths.  This
   document extends the use of the IGP Flex Algorithm to satisfy network
   slicing scenarios.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on May 30, 2020.

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
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   to this document.  Code Components extracted from this document must



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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.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  SR Policy Using Slice-based Resources . . . . . . . . . . . .   3
   4.  SR Policy Optimaztion with IGP Flex-algo  . . . . . . . . . .   3
   5.  IGP Flex-algo Enhancement with AII  . . . . . . . . . . . . .   4
   6.  AII of FAD Sub-TLV  . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  ISIS AII of FAD Sub-TLV . . . . . . . . . . . . . . . . .   5
     6.2.  OSPF AII of FAD Sub-TLV . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  ISIS IANA Considerations  . . . . . . . . . . . . . . . .   6
     7.2.  OSPF IANA Considerations  . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   IGP Flex Algorithm [I-D.ietf-lsr-flex-algo] proposes a solution that
   allows IGPs themselves to compute constraint based paths over the
   network, and it also specifies a way of using Segment Routing (SR)
   Prefix-SIDs and SRv6 locators to steer packets along the constraint-
   based paths.  It specifies a set of extensions to ISIS, OSPFv2 and
   OSPFv3 that enable a router to send TLVs that identify (a)
   calculation-type, (b) specify a metric-type, and (c )describe a set
   of constraints on the topology, that are to be used to compute the
   best paths along the constrained topology.  A given combination of
   calculation-type, metric-type, and constraints is known as an FAD
   (Flexible Algorithm Definition).

   [I-D.peng-teas-network-slicing] proposes a solution to extend the
   control plane of transport network to instantiate the Network Slice
   Instance (NSI) in transport network.  A new identifier, AII, instead
   of existing TE affinity or other identifiers, is introduced to
   represent a TN-slice and specify the dedicated resource for the TN-
   slice.

   This document extends the FAD of IGP Flex Algorithm to let IGPs
   compute constraint based paths limited in specific TN-slice.






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

3.  SR Policy Using Slice-based Resources

   [I-D.ietf-spring-segment-routing-policy] details the concepts of SR
   Policy and steering into an SR Policy.  These apply equally to the
   MPLS and IPv6 (known as SRv6) data plane instantiations of Segment
   Routing with their respective representations of segments as SR-MPLS
   SID and SRv6 SID as described in [RFC8402].  The color of SR policy
   defines a TE purpose, which includes a set of constraints such as
   bandwidth, delay, TE metric, etc.

   The overlay service can select underlay SR policy according to a
   meaningful color value.  From the perspective of service, color is
   the key to get the expected SLA, and it is a global administrative
   configuration or setting that could be exchangeable between two
   devices for SR policy on-demand next-hop triggering.  The service
   never concern whether the underlay network has been partitioned as
   multi-domains, or multi-topologies.  That is, color has not semantic
   local within one domain, or one topology.  Instead, any type of
   resources such as topology, computation, storage could be selected by
   the color template.  In this sense, TN-slices are also high-level
   resouces that could be selected by color template.  A simple way to
   achieve this is to contain the specific AII information in the color
   template, to restrict the TE path to the corresponding TN-slice.

4.  SR Policy Optimaztion with IGP Flex-algo

   Indeed, FA-id defined in [I-D.ietf-lsr-flex-algo] is a short mapping
   of SR policy color to optimaze segment stack depth for the IGP area
   partial of the entire SR policy.  The overlay service that want to be
   carried over a particual SR-FA path must firstly let the SR policy
   supplier know that requirement.  There are two possible ways to map a
   color to an FA-id.  One is explicit mapping configuration within
   color template, the other is dynamic to replace a long segment list
   to short FA segment by headend or controller once the creterias
   contained in the color-template equal to that contained in FAD.

   [I-D.ietf-lsr-flex-algo] described that Application specific Flex-
   Algorithm participation advertisements MAY be topology specific or
   MAY be topology independent, and also emphasize that Segment Routing
   Flex-Algorithm participation advertisement is topology independent,



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   i.e., when a router advertises participation in an SR-Algorithm, the
   participation applies to all topologies in which the advertising node
   participates.  Here the topology means Multi-Topology Routing (MTR)
   described in [RFC5120], [RFC4915], [RFC5340].  [RFC8402] also
   mentioned that multiple SIDs MAY be allocated to the same prefix so
   long as the tuple <prefix, topology, algorithm> is unique.  In fact,
   this will lead to many forwarding tables, such as table per topology,
   table per each combined tuple <topology, algorithm>.

   According to [I-D.peng-teas-network-slicing], we donot use MTR to
   identify the TN-slice and partition the virtual topology for the TN-
   slice.  Instead, a slice-based identifier AII is introduced to
   represent a TN-slice, and the first feature of AII is a TE criteria
   for TE service just like AG/EAG.  In order to make the contents of
   the color template and mapping FAD consistent, AII is also necessary
   put into FAD.

   Although the network operator may change the AII information within
   the FAD for the specific FA-id, there is only one forwarding table
   with constant table ID, i.e., FA-id.  Note that there are also
   independent forwarding tables per AII, but not those per tuple <AII,
   FA-id>.  That is, FA-id has not semantic local within AII, as the
   same as color.

5.  IGP Flex-algo Enhancement with AII

   FAD that contains AII information will enhance the capability of
   Flex-algo to support network slicing.  For example, Loop Free
   Alternate (LFA) paths for a given Flex-Algorithm can include Prefix-
   SIDs advertised specifically for the given algorithm, and especially
   Adjacency-SIDs for the specific AII.  When different FA planes share
   the same link resouce, Adjacency-SID per AII (according to
   [I-D.peng-teas-network-slicing]) can distinguish the flow of
   different slices well and provide different treatment.

   The following figure shows an example of Flex-algo enhancement with
   AII.

                        [S1]--------[D]--------[S2]
                         |           |          |
                         |           |          |
                         |           |          |
                        [A]---------[B]--------[C]


                 Figure 1: Flex-algo Enhancement with AII





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   Suppose that node S1, A, B, D and their inter-connected links belongs
   to FA-id 128 plane as well as AII-1, and S2, B, C, D and their inter-
   connected links belongs to FA-id 129 plane as well as AII-2.  The IGP
   metric of link B-D is 100, and all other links have IGP metric 1.  In
   FA-id 128 plane, from S1 to destination D, the primary path is S1-D,
   and the TI-LFA backup path is segment list {node(B), adjacency(B-D)}.
   Similarly, In FA-id 129 plane, from S2 to destination D, the primary
   path is S2-D, and the TI-LFA backup path is segment list {node(B),
   adjacency(B-D)}. With the help of AII parameter contained in the FAD,
   the above TI-LFA path of FA-id 128 plane will be translated to {node-
   SID(B)@FA-id128, adjacency-SID(B-D)@AII-1}, and TI-LFA path of FA-id
   129 plane will be translate to {node-SID(B)@FA-id129, adjacency-
   SID(B-D)@AII-2}. So that node B can distinguish the flow of FA-id 128
   and FA-id 129 with different treatment (e.g., QoS) and send to the
   same outgoing link B-D.

   For inter-domain case, different domain can config different FA-id
   independently, but they can contain the same AII to construct an E2E
   slice-based SR policy.  IGP flex-algo is responsible for creating
   constraint based paths within the domain according to FAD including
   AII parameter, and BGP-LU or SDN controller is responsible for
   selecting inter-domain links according to color template including
   AII parameter.  AII is easy to address the requirement of E2E Slicing
   view.

6.  AII of FAD Sub-TLV

6.1.  ISIS AII of FAD Sub-TLV

   ISIS AII of FAD Sub-TLV is used to advertise the AII information that
   is used during the Flex-Algorithm path calculation.  It is a Sub-TLV
   of the ISIS FAD Sub-TLV.  It has the following format:

       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     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               AII                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                 Figure 2: ISIS AII of FAD Sub-TLV format

   where:

   Type: TBD1.




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   Length: 4 octets.

   AII: Administrative Instance Identifier as defined in
   [I-D.peng-teas-network-slicing].

   ISIS AII of FAD Sub-TLV MAY NOT appear more then once in an ISIS FAD
   Sub-TLV.  If it appears more then once, the ISIS FAD Sub-TLV MUST be
   ignored by the receiver.

6.2.  OSPF AII of FAD Sub-TLV

   OSPF AII of FAD Sub-TLV is used to advertise the AII information that
   is used during the Flex-Algorithm path calculation.  It is a Sub-TLV
   of the OSPF FAD TLV.  It has the following format:

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              AII                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                 Figure 3: OSPF AII of FAD Sub-TLV format

   where:

   Type: TBD2.

   Length: 4 octets.

   AII: Administrative Instance Identifier as defined in
   [I-D.peng-teas-network-slicing].

   OSPF AII of FAD Sub-TLV MAY NOT appear more then once in an OSPF FAD
   TLV.  If it appears more then once, the OSPF FAD TLV MUST be ignored
   by the receiver.

7.  IANA Considerations

7.1.  ISIS IANA Considerations

   This document defines the following Sub-Sub-TLVs in the "Sub-Sub-TLVs
   for Flexible Algorithm Definition Sub-TLV" registry:

   Type: TBD1




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   Description: Administrative Instance Identifier

   Reference: This document (Section 6.1)

7.2.  OSPF IANA Considerations

   This document registers following Sub-TLVs in the "TLVs for Flexible
   Algorithm Definition TLV" registry:

   Type: TBD2

   Description: Administrative Instance Identifier

   Reference: This document (Section 6.2)

8.  Security Considerations

   This specification inherits all security considerations of
   [I-D.ietf-lsr-flex-algo].

9.  Acknowledgements

   TBD

10.  Normative References

   [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-05 (work in progress), November 2019.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-05 (work in progress),
              November 2019.

   [I-D.peng-teas-network-slicing]
              Peng, S., Chen, R., Mirsky, G., and F. Qin, "Packet
              Network Slicing using Segment Routing", draft-peng-teas-
              network-slicing-01 (work in progress), November 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>.





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

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

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

   [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>.

Authors' Addresses

   Peng Shaofu
   ZTE Corporation
   No.68 Zijinghua Road, Yuhuatai District
   Nanjing
   China

   Email: peng.shaofu@zte.com.cn


   Chen Ran
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing
   China

   Email: chen.ran@zte.com.cn


   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com



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