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Network Work group                                        N. Nainar, Ed.
Internet-Draft                                         C. Pignataro, Ed.
Intended status: Standards Track                                  Z. Ali
Expires: September 10, 2020                                  C. Filsfils
                                                                   Cisco
                                                           March 9, 2020


  Segment Routing Generic TLV for MPLS Label Switched Path (LSP) Ping/
                               Traceroute
          draft-nainar-mpls-spring-lsp-ping-sr-generic-sid-02

Abstract

   RFC8402 introduces Segment Routing architecture that leverages source
   routing and tunneling paradigms and can be directly applied to the
   Multi Protocol Label Switching (MPLS) data plane.  A node steers a
   packet through a controlled set of instructions called segments, by
   prepending the packet with Segment Routing header.  SR architecture
   defines different types of segments with different forwarding
   semantics associated.  SR can be applied to the MPLS directly and to
   IPv6 dataplane using a new routing header.

   RFC8287 defines the extensions to MPLS LSP Ping and Traceroute for
   Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifier
   (SIDs) with an MPLS data plane.  Various SIDs are proposed as part of
   SR architecture with different associated instructions that raises a
   need to come up with new Target FEC Stack Sub-TLV for each such SIDs.

   This document defines a new Target FEC Stack Sub-TLV that is used to
   validate the instruction associated with any SID.

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 September 10, 2020.



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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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Challenges with Existing Mechanism  . . . . . . . . . . .   3
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Target FEC Stack sub-TLV for Segment Routing SID  . . . . . .   4
     4.1.  Segment Routing Generic Label . . . . . . . . . . . . . .   4
     4.2.  FEC for Path validation . . . . . . . . . . . . . . . . .   4
   5.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  SID to Interface Mapping  . . . . . . . . . . . . . . . .   5
     5.2.  Initiator behavior  . . . . . . . . . . . . . . . . . . .   6
       5.2.1.  SRGL in Target FEC Stack TLV  . . . . . . . . . . . .   6
     5.3.  Responder behavior  . . . . . . . . . . . . . . . . . . .   7
     5.4.  PHP flag behavior . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  New Target FEC Stack Sub-TLVs . . . . . . . . . . . . . .   8
     6.2.  Security Considerations . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC8402] introduces and describes a Segment Routing architecture
   that leverages the source routing and tunneling paradigms.  A node
   steers a packet through a controlled set of instructions called
   segments, by prepending the packet with Segment Routing header.  A
   detailed definition of the Segment Routing architecture is available
   in [RFC8402]



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   As described in [RFC8402] and [I-D.ietf-spring-segment-routing-mpls],
   the Segment Routing architecture can be directly applied to an MPLS
   data plane, the Segment identifier (Segment ID) will be of 20-bits
   size and the Segment Routing header is the label stack.

1.1.  Challenges with Existing Mechanism

   [RFC8287] defines the mechanism to perform LSP Ping and Traceroute
   for Segment Routing with MPLS data plane.  [RFC8287] defines the
   Target FEC Stack Sub-TLVs for IGP-Prefix Segment ID and IGP-Adjacency
   Segment ID.

   There are various other Segment IDs proposed by different documents
   that are applicable for SR architecture.
   [I-D.ietf-idr-bgp-prefix-sid] defines BGP Prefix Segment ID,
   [I-D.ietf-idr-bgpls-segment-routing-epe] defines BGP Peering Segment
   ID such as Peer Node SID, Peer Adj SID and Peer Set SID.
   [I-D.sivabalan-pce-binding-label-sid] defines Path Binding Segment
   ID.  As SR evolves for different usecases, we may see more types of
   SIDs defined in the future.  This raises a need to propose new Target
   FEC Stack Sub-TLV for each such Segment ID that may need specific or
   network wide software upgrade to support such new Target FEC Stack
   Sub-TLVs.

   So instead of proposing different Target FEC Stack Sub-TLV for each
   SID, this document attempt to propose a SR Generic Label Sub-TLV for
   Target FEC Stack TLV with the procedure to validate the associated
   instruction.

   This document describes the new Target FEC Stack Sub-TLV that carries
   the SID and the procedure to use LSP Ping and Traceroute using the
   new sub-tlv to support path validation and fault isolation for any SR
   Segment IDs.

2.  Requirements notation

   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 RFC
   2119 [RFC2119] RFC 8174 [RFC8174] when and only when, they appear in
   all capitals, as shown here.

3.  Terminology

   This document uses the terminologies defined in [RFC8402], [RFC8029],
   readers are expected to be familiar with it.





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4.  Target FEC Stack sub-TLV for Segment Routing SID

   Following the procedure defined in [RFC8029], below defined Target
   FEC Stack Sub-TLV will be included for each labels in the stack.  The
   below Sub-TLV is defined for Target FEC Stack TLV (Type 1), the
   Reverse-Path Target FEC Stack TLV (Type 16), and the Reply Path TLV
   (Type 21).

           sub-Type    Value Field
           --------  ---------------
            TBD1      Segment Routing Generic Label (SRGL)


4.1.  Segment Routing Generic Label

   The format of the Sub-TLV is as specified 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             SR SID                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   SR SID

      Carries 20 bits of Segment ID that is used for validating the
      instruction.

4.2.  FEC for Path validation

   In SR architecture, any SID is associated with topology or service
   instruction.  While the topology instruction steers the packet over
   best path or specific path, the service instruction instructs the
   type of service to be applied on the packet.















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                  R3-------R6      L1
                 /           \  +-------+
                /             \ |  L2   |
        R1----R2               R7------R8
                \             /
                 \           /
                  R4-------R5

          Figure 1: Segment Routing network

 The Node Segment IDs for Rx for Algo 0 is 16000x. (Ex: For R1, it is 160001)
 The Node Segment IDs for Rx for Algo 128 is 16128x. (Ex: For R1, it is 161281)

 9178 --> Adjacency Segment ID from R7 to R8 over link L1.
 9278 --> Adjacency Segment ID from R7 to R8 over link L2.
 9378 --> Parallel Adjacency Segment ID from R7 to R8 over Link L1 or L2.
 9187 --> Adjacency Segment ID from R8 to R7 over link L1.
 9287 --> Adjacency Segment ID from R8 to R7 over link L2.
 9387 --> Parallel Adjacency Segment ID from R8 to R7 over Link L1 or L2.

   The instruction associated with any SID can be validated by verifying
   if the segment is terminated on the correct node and optionally
   received over the correct incoming interface.  In Figure 1, inorder
   to validate the SID 9178, R1 can use {(SID=9178)} as FEC in Target
   FEC Stack Sub-TLV.

5.  Procedures

   This section describes the procedure to validate SR Generic Label
   Sub-TLV.

5.1.  SID to Interface Mapping

   Any End point MAY maintain a SID to Interface mapping table that
   maintains the below:

   o  All the local Prefix/Node SID with any SR enabled interface as
      incoming interface.

   o  All the Adj-SIDs assigned by directly connected remote nodes with
      the relevant interface incoming interface.

   In Figure 1, R8 maintains 160008 and 161288 with Incoming interface
   as any SR enabled interface.  Similarly, R8 maintains 9178 with Link
   L1 as incoming interface, 9278 with Link L2 as incoming interface and
   9378 with Link L1 or L2 as incoming interface.





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   How this mapping is populated and maintained is a local
   implementation matter.  It can be populated based on the IGP database
   or can be based on a query to Path Computation Element (PCE)
   controller.  The mapping can be persistent or on-demand triggered by
   receiving LSP Ping Request.

5.2.  Initiator behavior

   This section defines the Target FEC Stack TLV construction mechanism
   by an initiator when using SR Generic Label Sub-TLV.

      Ping

         Initiator MUST include FEC(s) corresponding to the destination
         segment.

         Initiator MAY include FECs corresponding to some or all of
         segments imposed in the label stack by the initiator to
         communicate the segments traversed.

      Traceroute

         Initiator MUST initially include FECs corresponding to all of
         segments imposed in the label stack.

         When a received echo reply contains FEC Stack Change TLV with
         one or more of original segment(s) being popped, initiator MAY
         remove corresponding FEC(s) from Target FEC Stack TLV in the
         next (TTL+1) traceroute request as defined in section 4.6 of
         [RFC8029].

         When a received echo reply does not contain FEC Stack Change
         TLV, initiator MUST NOT attempt to remove FEC(s) from Target
         FEC Stack TLV in the next (TTL+1) traceroute request.

5.2.1.  SRGL in Target FEC Stack TLV

   When the last segment ID in the label stack is IGP Prefix SID, Adj-
   SID, Binding SID, BGP Prefix SID or BGP Peering SID, set the SR SID
   field to the Segment ID value derived based on the index and the SRGB
   advertised by the LSP End Point.

   How the above values are derived is a local implementation matter.
   It can be manually defined using CLI knob while triggering the LSP
   Ping Request or can use other mechanisms like querying the local
   database.





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5.3.  Responder behavior

   Step 4a defined in Section 7.4 of [RFC8287] is updated as below:

      If the Label-stack-depth is 0 and Target FEC Stack Sub-TLV at FEC-
      stack-depth is TBD1 (SRGL) {

      *  Set the Best-return-code to 10 when the responding node is not
         the LSP End Point for SR SID.

      *  Set the Best-return-code to 35, if Interface-I does not match
         the SID to Interface mapping for the received SR SID.

      *  set FEC-Status to 1, and return.

      }

      If the Label-stack-depth is greater than 0 and Target FEC Stack
      Sub-TLV at FEC-stack-depth is TBD1 (SRGL), {

      *  If the Label at Label-stack-depth is Imp-null {

         +  Set the Best-return-code to 10 when the responding node is
            not the LSP End Point for the SR SID.

         +  Set the Best-return-code to 35, if Interface-I does not
            match the SID to Interface mapping for the received SR SID.

         +  set FEC-Status to 1, and return.

         }

      *  Else:

         +  Set the Best-return-code to 10 when the index derived from
            the label at Label-stack-depth is not advertised by LSP End
            Point.

         +  set FEC-Status to 1, and return.

      }

5.4.  PHP flag behavior

   Section 7.2 of [RFC8287] explains the behavior for FEC stack change
   for Adjacency Segment ID.  The same procedure is applicable for BGP
   Peering SID as well.




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6.  IANA Considerations

6.1.  New Target FEC Stack Sub-TLVs

   IANA is requested to assign three new Sub-TLVs from "Sub-TLVs for TLV
   Types 1, 16 and 21" sub-registry from the "Multi-Protocol Label
   Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
   [IANA-MPLS-LSP-PING] registry.

   Sub-Type    Sub-TLV Name                 Reference
   --------    -----------------            ------------
     TBD1    Segment Routing Generic Label Section 4.1 of this document

6.2.  Security Considerations

   This document defines additional MPLS LSP Ping Sub-TLVs and follows
   the mechanisms defined in [RFC8029].  All the security considerations
   defined in [RFC8029] will be applicable for this document, and in
   addition, they do not impose any additional security challenges to be
   considered.

7.  Acknowledgement

   TBD

8.  Contributors

   Danial Johari, Cisco Systems

9.  References

9.1.  Normative References

   [I-D.ietf-idr-bgp-prefix-sid]
              Previdi, S., Filsfils, C., Lindem, A., Sreekantiah, A.,
              and H. Gredler, "Segment Routing Prefix SID extensions for
              BGP", draft-ietf-idr-bgp-prefix-sid-27 (work in progress),
              June 2018.

   [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.







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   [I-D.sivabalan-pce-binding-label-sid]
              Sivabalan, S., Filsfils, C., Tantsura, J., Hardwick, J.,
              Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
              in PCE-based Networks.", draft-sivabalan-pce-binding-
              label-sid-07 (work in progress), July 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>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [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>.

   [RFC8287]  Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
              N., Kini, S., and M. Chen, "Label Switched Path (LSP)
              Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
              IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
              Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
              <https://www.rfc-editor.org/info/rfc8287>.

   [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>.

9.2.  Informative References

   [I-D.ietf-spring-segment-routing-mpls]
              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-22
              (work in progress), May 2019.

   [IANA-MPLS-LSP-PING]
              IANA, "Multi-Protocol Label Switching (MPLS) Label
              Switched Paths (LSPs) Ping Parameters",
              <http://www.iana.org/assignments/mpls-lsp-ping-parameters/
              mpls-lsp-ping-parameters.xhtml>.





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Authors' Addresses

   Nagendra Kumar Nainar (editor)
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709-4987
   US

   Email: naikumar@cisco.com


   Carlos Pignataro (editor)
   Cisco Systems, Inc.
   7200-11 Kit Creek Road
   Research Triangle Park, NC  27709-4987
   US

   Email: cpignata@cisco.com


   Zafar Ali
   Cisco Systems, Inc.

   Email: zali@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.

   Email: cfilsfil@cisco.com





















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