Internet DRAFT - draft-filsfils-spring-path-tracing-srmpls

draft-filsfils-spring-path-tracing-srmpls







SPRING                                                       C. Filsfils
Internet-Draft                                        A. Abdelsalam, Ed.
Intended status: Standards Track                       P. Camarillo, Ed.
Expires: 21 May 2024                                 Cisco Systems, Inc.
                                                               I. Meilik
                                                                Broadcom
                                                            M. Valentine
                                                           Goldman Sachs
                                                                 R. Geib
                                                        Deutsche Telekom
                                                            J. Desmarais
                                                Colt Technology Services
                                                        18 November 2023


                    Path Tracing in SR-MPLS networks
              draft-filsfils-spring-path-tracing-srmpls-03

Abstract

   Path Tracing provides a record of the packet path as a sequence of
   interface ids.  In addition, it provides a record of end-to-end
   delay, per-hop delay, and load on each interface that forwards the
   packet.

   Path Tracing has the lowest MTU overhead compared to alternative
   proposals such as [INT], [RFC9197], [I-D.song-opsawg-ifit-framework],
   and [I-D.kumar-ippm-ifa].

   Path Tracing supports fine grained timestamp.  It has been designed
   for linerate hardware implementation in the base pipeline.

   This document defines the Path Tracing specification for the SR-MPLS
   dataplane.  The Path Tracing specification for the SRv6 dataplane is
   defined in [I-D.filsfils-spring-path-tracing].

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/.






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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 21 May 2024.

Copyright Notice

   Copyright (c) 2023 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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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  PT Source Node Dataplane Behavior . . . . . . . . . . . . . .   4
   4.  PT Midpoint Node Dataplane Behavior . . . . . . . . . . . . .   5
   5.  PT Sink Node Dataplane Behavior . . . . . . . . . . . . . . .   5
   6.  PT Headers  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  MPLS Hop-by-Hop Path Tracing Option . . . . . . . . . . .   6
   7.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Path Tracing provides a record of the packet path as a sequence of
   interface ids.  In addition, it provides a record of end-to-end
   delay, per-hop delay, and load on each interface that forwards the
   packet.





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   Path Tracing has the lowest MTU overhead compared to alternative
   proposals such as [INT], [RFC9197], [I-D.song-opsawg-ifit-framework],
   and [I-D.kumar-ippm-ifa].

   Path Tracing supports fine grained timestamp.  It has been designed
   for linerate hardware implementation in the base pipeline.

   Path Tracing is applicable to both SR-MPLS [RFC8660], as well as SRv6
   [RFC8986].  This document defines the Path Tracing specification for
   the SR-MPLS dataplane.  The SRv6 dataplane is detailed in
   [I-D.filsfils-spring-path-tracing].

2.  Terminology

   The following terms used within this document are defined in
   [RFC6790], [RFC8402], [RFC8754], [RFC8986],
   [I-D.decraene-mpls-slid-encoded-entropy-label-id] and
   [I-D.filsfils-spring-path-tracing]: Segment Routing (SR), SR Domain,
   Segment Identifier (SID), SR-MPLS SID, SR Policy, Segment Routing
   Header (SRH), SR source node, transit node, SR Endpoint, SA, DA, EL,
   ELI, ELC, PT, PT Probing Instance, PT Source, PT Midpoint, PT Sink,
   RC, MCD, SRH PT-TLV, TEF.

   The following terms are used in this document as defined below:

   MPLS HbH-PT: MPLS Hop-by-Hop Path Tracing Option used for Path
   Tracing.  It contains a stack of MCDs.  It is defined in Section 6.1
   of this document.

   SEL: Structured Entropy Label as defined in
   [I-D.decraene-mpls-slid-encoded-entropy-label-id].

   TEF Label: MPLS Label bound to Timestamp, Encapsulation and Forward
   (TEF) behavior.  The allocation of the TEF Label is out of scope of
   this document.

   PTI: PT Indicator is a flag bit used to indicate the presence of the
   MPLS HbH-PT after the BoS Label and triggers PT behavior at a PT
   Midpoint.

2.1.  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.




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3.  PT Source Node Dataplane Behavior

   For each configured PT Probing Instance, according to the probe-rate,
   the PT Source generates a PT probe packet as follows:

   S01. Generate a new packet
   S02. Push an SRH PT-TLV
   S03. Set the session ID field of the SRH PT-TLV as per
        PT Probing Instance configuration
   S04. Set the Sequence Number field of SRH PT-TLV and
        increase local counter
   S05. Push an MPLS HbH-PT header
   S06. Set all bits of MCD Stack of the MPLS HbH-PT header to zero
   S07. Set the VER field of the MPLS HbH-PT to 0x2
   S08. Set the value of Opt Data Len field as per
        the PT Probing Instance configuration
   S09. Push an MPLS Structured Entropy Label (SEL)
   S10. Set the PTI flag in the ELC field of the SEL
   S11. Set the value of the SEL entropy field as per
        the PT Probing Instance configuration
   S12. Set Bottom of Stack bit (S) of the SEL to 1
   S13. Push an MPLS Entropy Indicator Label (ELI)
   S14. Push an MPLS TEF Label as per the PT Probing
        Instance configuration
   S15. Set the TC and TTL value of the TEF Label as per
        PT Probing Instance configuration
   S16. Push an SR-MPLS transport Label stack as per the
        PT Probing Instance configuration
   S17. Set the TC and TTL value of the SR-MPLS transport Labels
        as per PT Probing Instance configuration
   S18. Add padding bytes after SRH PT-TLV to reach the desired
        packet size as per the MTU sweeping range configuration in
        the PT Probing Instance configuration
   S19. Perform MPLS lookup using the topmost label to
        determine the Outgoing Interface (IFACE-OUT)
   S20. Record Transmit 64-bit timestamp (SRC.T64) in the
        T64 field of the SRH PT-TLV
   S21. Record IFACE-OUT ID (SRC.OIF) in the IF_ID field
        of the SRH PT-TLV
   S22. Record IFACE-OUT Load (SRC.OIL) in the IF_LD field
        of the SRH PT-TLV
   S23. Forward the packet via IFACE-OUT

   Notes:







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   *  The pseudocode describes local processing at a node.  An
      implementation of the pseudocode is compliant as long as the
      externally observable wire protocol is as described in the
      pseudocode.

4.  PT Midpoint Node Dataplane Behavior

   When an MPLS LSR router receives an MPLS packet with SEL, the MPLS
   LSR router processes the SEL as follows:

   S01. When processing SEL {
   S02.    Use Entropy field to compute ECMP hash and decide IFACE-OUT
   S03.    IF (SEL[ELC].PTI == 1 and SEL[BOS] == 1) {
   S04.       Compute the Midpoint MCD for IFACE-OUT
   S05.       Locate the MPLS HbH-PT immediately after SEL
   S06.       MPLS_HbH-PT.MCD_Stack[3:Opt_Data_Len -1] =
              MPLS_HbH-PT.MCD_Stack[0:Opt_Data_Len -4]
                 //Shift MCD Stack 3Bytes to the right
   S07.       MPLS_HbH-PT.MCD_Stack[0:2] = MCD[0:2]
                //i.e., Push the MCD at the beginning of the Stack
   S08.    }
   S09. }

   Notes:

   *  The PT Midpoint behavior MUST be implemented in the normal
      pipeline to experience the regular datapath (i.e., linerate).
      Offloading the processing of this option to either the slow-path
      or a co-processors is not acceptable and yields invalid results.

5.  PT Sink Node Dataplane Behavior

   We define a new MPLS Label bound to an SRv6 Policy with Timestamp,
   Encapsulation and Forward ("TEF Label" for short).  When Node N
   receives an MPLS packet with topmost Label is TEF Label, N performs
   the TEF behavior to the MPLS packet.















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   S01. Record Rx 64-bit timestamp (SNK.T64)
   S02. Record incoming interface ID (Sink.IIF)
   S03. Record incoming interface Load (Sink.IIL)
   S04. Push a new IPv6 header
   S05. Set the IPv6 SA to the Sink node loopback
   S06. Set the IPv6 DA to the first SID in the SRv6 SID List
   S07. Set the IPv6 Next Header field to 43 (SRH)
   S08. Append an SRH
   S09. Set the SRH Next Header field to 137 (MPLS)
   S10. Write the SID list in the SRH
   S11. Append an SRH PT-TLV
   S12. Set the session ID field of the SRH PT-TLV to zero
   S13. Set the Sequence Number field of the SRH PT-TLV to zero
   S14. Write Sink.T64 in the T64 field of the SRH PT-TLV
   S15. Write Sink.IIF in the IF_ID field of the SRH PT-TLV
   S16. Write Sink.IIL in the IF_LD field of the SRH PT-TLV
   S17. Perform an IPv6 lookup and forward the packet

   Notes:

   *  The pseudocode describes local processing at a node.  An
      implementation of the pseudocode is compliant as long as the
      externally observable wire protocol is as described in the
      pseudocode.

6.  PT Headers

6.1.  MPLS Hop-by-Hop Path Tracing Option

   We define a new header called MPLS Hop-by-Hop Path Tracing option
   ("MPLS HbH-PT" for short).  The header is used to collect the MCD of
   each PT Midpoint on the packet path.  The MPLS HbH-PT has the
   following format:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  VER  |  RSVD |  Opt Data Len |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   ~                           MCD Stack                           ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 1: IPv6 Hop-by-Hop Path Tracing Option Format

   Where:

   *  VER: In MPLS, the first nibble after the Label stack indicates the
      packet IP protocol version.  VER is set to 0x2.



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   *  RSVD: Reserved 4-bits.  Currently not used.

   *  Opt Data Len: carries the length of MCD stack (in bytes).  Used by
      PT Midpoint to determine the MCD stack shift value.

   *  MCD Stack: used to collect the MCDs from PT Midpoints

   Note: The MPLS Hop-by-Hop Path Tracing option has a variable length.
   The operator, upon configuring the Source node behavior, MUST select
   an option length that is supported by all the routers in the network.

7.  Benefits

   *  Insignificant MTU overhead:

      -  PT has the lowest MTU overhead compared to alternative
         solutions such as [INT], [RFC9197],
         [I-D.song-opsawg-ifit-framework], and [I-D.kumar-ippm-ifa].

   *  Linerate and HW friendliness:

      -  Designed for linerate hardware implementation, using the
         regular forwarding pipeline.  No offloading to co-processors
         whose databases might defer from forwarding pipeline.

      -  Leverages mature hardware capabilities (basic shift operation);
         no packet resizing at every node along the path

   *  Scalable Fine-grained Timestamp:

      -  64-bits timestamp at PT SRC and PT SNK

      -  8-bits truncated timestamp at PT Midpoint leveraging flexible
         per-outgoing-link template allowing diverse link types in the
         same measurement (e.g., DC, metro, WAN)

   *  Scalable Load measurement

8.  Security Considerations

   TBD

9.  IANA Considerations

   TBD

10.  References




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10.1.  Normative References

   [I-D.decraene-mpls-slid-encoded-entropy-label-id]
              Decraene, B., Filsfils, C., Henderickx, W., Saad, T.,
              Beeram, V. P., and L. Jalil, "Using Entropy Label for
              Network Slice Identification in MPLS networks.", Work in
              Progress, Internet-Draft, draft-decraene-mpls-slid-
              encoded-entropy-label-id-05, 12 December 2022,
              <https://datatracker.ietf.org/doc/html/draft-decraene-
              mpls-slid-encoded-entropy-label-id-05>.

   [I-D.filsfils-spring-path-tracing]
              Filsfils, C., Abdelsalam, A., Camarillo, P., Yufit, M.,
              Graf, T., Su, Y., Matsushima, S., Valentine, M., and
              Dhamija, "Path Tracing in SRv6 networks", Work in
              Progress, Internet-Draft, draft-filsfils-spring-path-
              tracing-05, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-filsfils-
              spring-path-tracing-05>.

   [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>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [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>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.







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   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

10.2.  Informative References

   [I-D.kumar-ippm-ifa]
              Kumar, J., Anubolu, S., Lemon, J., Manur, R., Holbrook,
              H., Ghanwani, A., Cai, D., Ou, H., Li, Y., and X. Wang,
              "Inband Flow Analyzer", Work in Progress, Internet-Draft,
              draft-kumar-ippm-ifa-07, 7 September 2023,
              <https://datatracker.ietf.org/doc/html/draft-kumar-ippm-
              ifa-07>.

   [I-D.song-opsawg-ifit-framework]
              Song, H., Qin, F., Chen, H., Jin, J., and J. Shin,
              "Framework for In-situ Flow Information Telemetry", Work
              in Progress, Internet-Draft, draft-song-opsawg-ifit-
              framework-21, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-song-opsawg-
              ifit-framework-21>.

   [INT]      "In-band Network Telemetry (INT) Dataplane Specification",
              2020, <https://github.com/p4lang/p4-
              applications/blob/master/docs/INT_v2_1.pdf>.

   [RFC9197]  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
              Ed., "Data Fields for In Situ Operations, Administration,
              and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
              May 2022, <https://www.rfc-editor.org/info/rfc9197>.

Contributors

   Jisu Bhattacharya
   Cisco Systems, Inc.
   United States of America
   Email: jisu@cisco.com







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   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com


   Shay Zadok
   Broadcom
   Israel
   Email: shay.zadok@broadcom.com


   Mark Yufit
   Broadcom
   Israel
   Email: mark.yufit@broadcom.com


   Bart Janssens
   Colt Technology Services
   Belgium
   Email: Bart.Janssens@colt.net


Authors' Addresses

   Clarence Filsfils
   Cisco Systems, Inc.
   Belgium
   Email: cf@cisco.com


   Ahmed Abdelsalam (editor)
   Cisco Systems, Inc.
   Italy
   Email: ahabdels@cisco.com


   Pablo Camarillo Garvia (editor)
   Cisco Systems, Inc.
   Spain
   Email: pcamaril@cisco.com


   Israel Meilik
   Broadcom
   Israel
   Email: israel.meilik@broadcom.com



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   Mike Valentine
   Goldman Sachs
   United States of America
   Email: michael.j.valentine@gs.com


   Ruediger Geib
   Deutsche Telekom
   Germany
   Email: Ruediger.Geib@telekom.de


   Jonathan Desmarais
   Colt Technology Services
   United Kingdom
   Email: Jonathan.Desmarais@colt.net



































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