MPLS Working Group                                               T. Saad
Internet-Draft                                          Juniper Networks
Intended status: Informational                              K. Makhijani
Expires: 11 July 2022                                            H. Song
                                                  Futurewei Technologies
                                                          7 January 2022

            Usecases for MPLS Indicators and Ancillary Data


   This document presents a number of use cases that have a common need
   for encoding MPLS function indicators and ancillary data inside MPLS
   packets.  The use cases described are not an exhaustive set, but
   rather the ones that are actively discussed at the MPLS Working

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 11 July 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Acronyms and Abbreviations  . . . . . . . . . . . . . . .   3
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  In-situ OAM . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Network Slicing . . . . . . . . . . . . . . . . . . . . .   4
       2.2.1.  Global Identifier as Slice Selector . . . . . . . . .   5
       2.2.2.  Forwarding Label as a Slice Selector  . . . . . . . .   6
     2.3.  Time Sensitive Networking . . . . . . . . . . . . . . . .   6
       2.3.1.  Stack-based Methods for Latency Control . . . . . . .   6
       2.3.2.  Stack Entry Format  . . . . . . . . . . . . . . . . .   7
     2.4.  NSH Based Service Function Chaining . . . . . . . . . . .   7
     2.5.  Network Programming . . . . . . . . . . . . . . . . . . .   7
     2.6.  Application Aware Networking (APN)  . . . . . . . . . . .   8
   3.  Co-existence of Usecases  . . . . . . . . . . . . . . . . . .   8
     3.1.  IOAM with Network Slicing . . . . . . . . . . . . . . . .   8
     3.2.  IOAM with Time Sensitive Networking . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This document describes important cases that require carrying
   additional ancillary data within the MPLS packets, as well as the
   means to indicate ancillary data is present.

   These use cases have been identified by the MPLS working group design
   team working on defining MPLS function indicators and ancillary data
   for the MPLS data plane.  The use cases described in this document
   will be used to assist in identifying requirements and issues to be
   considered for future resolution by the working group.

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   *  ID: draft-gandhi-mpls-ioam describes applicability of IOAM to MPLS

   *  RFC 8986 describes the network programming usecase for SRv6

   *  RFC 8595 describes solution for MPLS-based forwarding for Service
      Function Chaining

1.1.  Terminology

   The following terminology is used in the document:

   IETF Network Slice:
      a well-defined composite of a set of endpoints, the connectivity
      requirements between subsets of these endpoints, and associated
      requirements; the term 'network slice' in this document refers to
      'IETF network slice' as defined in

   IETF Network Slice Controller (NSC):
      controller that is used to realize an IETF network slice

   Network Resource Partition:
      the collection of resources that are used to support a slice

   Time Sensitive Networking:
      Networks that transport time sensitive traffic.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

1.2.  Acronyms and Abbreviations

      MIAD: MPLS Label Stack Indicators for Ancillary Data

      ISD: In-stack data

      PSD: Post-stack data

      MPLS: Multiprotocol Label Switching

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2.  Use Cases

2.1.  In-situ OAM

   In-situ Operations, Administration, and Maintenance (IOAM) records
   operational and telemetry information within the packet while the
   packet traverses a particular path in a network domain.

   The term "in-situ" refers to the fact that the IOAM data fields are
   added to the data packets rather than being sent within the probe
   packets specifically dedicated to OAM or Performance Measurement

   IOAM can run in two modes End-to-End (E2E) and Hop-by-Hop (HbH).  In
   E2E mode, only the encapsulating and decapsulating nodes will process
   IOAM data fields.  In HbH mode, the encapsulating and decapsulating
   nodes as well as intermediate nodes process IOAM data fields.

   The IOAM data fields are defined in [I-D.ietf-ippm-ioam-data], and
   can be used for various use-cases of OAM and PM.

   [I-D.gandhi-mpls-ioam-sr] defines how IOAM data fields are
   transported using the MPLS data plane encapsulations, including
   Segment Routing (SR) with MPLS data plane (SR-MPLS).

   IOAM data are added after the bottom of the label stack.  The IOAM
   data fields can be of fixed or incremental size as defined in
   [I-D.ietf-ippm-ioam-data].  [I-D.gandhi-mpls-ioam] describes
   applicability of IOAM to MPLS dataplane.  The encapsulating MPLS node
   needs to know if the decapsulating MPLS node can process the IOAM
   data before adding it in the packet.

2.2.  Network Slicing

   [I-D.ietf-teas-ietf-network-slices] specifies the definition of a
   network slice for use within the IETF and discusses the general
   framework for requesting and operating IETF Network Slices, their
   characteristics, and the necessary system components and interfaces.

   Multiple network slices can be realized on top of a single shared

   In order to overcome scale challenges, IETF Network Slices may be
   aggregated into groups according to similar characteristics.  The
   slice aggregate [I-D.bestbar-teas-ns-packet] is a construct that
   comprises of the traffic flows of one or more IETF Network Slices of
   similar characteristics.

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   A router that requires forwarding of a packet that belongs to a slice
   aggregate may have to decide on the forwarding action to take based
   on selected next-hop(s), and the forwarding treatment (e.g.,
   scheduling and drop policy) to enforce based on the associated per-
   hop behavior.

   The routers in the network that forward traffic over links that are
   shared by multiple slice aggregates need to identify the slice
   aggregate packets in order to enforce the associated forwarding
   action and treatment.

   An IETF network slice need MAY support the following key features:

   1.  A Slice Selector

   2.  A Network Resource Partition associated with a slice aggregate.

   3.  A Path selection criteria

   4.  Verification that per slice SLOs are being met.  This may be done
       by active measurements (inferred) or by using IOAM.

   5.  Additionally, there is an on-going discussion on using Service
       Functions (SFs) with network slices.  This may require insertion
       of an NSH.

   6.  For multi-domain scenarios, a packet that traverses multiple
       domains may encode different identifiers within each domain.

2.2.1.  Global Identifier as Slice Selector

   A Global Identifier as a Slice Selector (GISS) can be encoded in the
   MPLS packet as defined in [I-D.kompella-mpls-mspl4fa],
   [], and
   [I-D.decraene-mpls-slid-encoded-entropy-label-id].  The Global
   Identifier Slice Selector can be used to associate the packets to the
   slice aggregate, independent of the MPLS forwarding label that is
   bound to the destination.  LSRs use the MPLS forwarding label to
   determine the forwarding next-hop(s), and use the Global Identifier
   Slice Selector field in the packet to infer the specific forwarding
   treatment that needs to be applied on the packet.

   The GISS can be encoded within an MPLS label that is carried in the
   packet's MPLS label stack.  All packets that belong to the same slice
   aggregate MAY carry the same GISS in the MPLS label stack.  It is
   also possible to have multiple GISS's map to the same slice
   aggregate.  The GISS can be encoded in an MPLS label and may appear
   in several positions in the MPLS label stack.

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2.2.2.  Forwarding Label as a Slice Selector

   [RFC3031] states in Section 2.1 that: 'Some routers analyze a
   packet's network layer header not merely to choose the packet's next
   hop, but also to determine a packet's "precedence" or "class of

   It is possible by assigning a unique MPLS forwarding label to each
   slice aggregate (FEC) to distinguish the packets forwarded to the
   same destination but that belong to different slice aggregates.  In
   this case, LSRs can use the top forwarding label to infer both the
   forwarding action and the forwarding treatment to be invoked on the
   packets.  A similar approach is described in
   [I-D.ietf-spring-resource-aware-segments] and

2.3.  Time Sensitive Networking

   The routers in a network can perform two distinct functions on
   incoming packets, namely forwarding (where the packet should be sent)
   and scheduling (when the packet should be sent).  Time Sensitive
   Networking (TSN) and Deterministic Networking provide several
   mechanisms for scheduling under the assumption that routers are time
   synchronized.  The most effective mechanisms for delay minimization
   involve per-flow resource allocation.

   Segment Routing (SR) is a forwarding paradigm that allows encoding
   forwarding instructions in the packet in a stack data structure,
   rather than being programmed into the routers.  The SR instructions
   are contained within a packet in the form of a first-in first-out
   stack dictating the forwarding decisions of successive routers.
   Segment routing may be used to choose a path sufficiently short to be
   capable of providing sufficiently low end- to-end latency but does
   not influence the queueing of individual packets in each router along
   that pat

   TSN is required for networks transporting time sensitive traffic,
   that is, packets that are required to be delivered to their final
   destination by a given time.

2.3.1.  Stack-based Methods for Latency Control

   One efficient data structure for inserting local deadlines into the
   headers is a "stack", similar to that used in Segment Routing to
   carry forwarding instructions.  The number of deadline values in the
   stack equals the number of routers the packet needs to traverse in
   the network, and each deadline value corresponds to a specific
   router.  The Top-of-Stack (ToS) corresponds to the first router's

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   deadline while the Bottom-of-Stack (BoS) refers to the last's.  All
   local deadlines in the stack are later or equal to the current time
   (upon which all routers agree), and times closer to the ToS are
   always earlier or equal to times closer to the BoS.

   The ingress router inserts the deadline stack into the packet
   headers; no other router needs to be aware of the requirements of the
   time sensitive flows.  Hence admitting a new flow only requires
   updating the information base of the ingress router.

   MPLS LSRs that expose the Top of Stack (ToS) label can also inspect
   the associated "deadline" carried in the packet (either in MPLS stack
   or after BoS).

2.3.2.  Stack Entry Format

   A number of different time formats commonly used in networking
   applications and can be used to encode the local deadlines.

   For the forwarding sub-entry we could adopt like SR-MPLS standard
   32-bit MPLS labels (which contain a 20-bit label and BoS bit), and
   thus SR-TSN stack entries could be 64-bits in size comprising a
   32-bit MPLS label and the aforementioned nonstandard 32-bit

   Alternatively, an SR-TSN stack entry could be 96 bits in length
   comprising a 32-bit MPLS label and either of the standardized 64-bit

2.4.  NSH Based Service Function Chaining

   The Network Service Header (NSH) can be embedded in an Extended
   Header (EH) to support the Path ID and any metadata that needs to be
   carried and exchanged between Service Function Forwarders (SFFs).

   A reference to the NSH SFC use case is defined in [RFC8596].

2.5.  Network Programming

   In SR, an ingress node steers a packet through an ordered list of
   instructions, called "segments".  Each one of these instructions
   represents a function to be called at a specific location in the
   network.  A function is locally defined on the node where it is
   executed and may range from simply moving forward in the segment list
   to any complex user-defined behavior.

   Network Programming combines Segment Routing (SR) functions to
   achieve a networking objective that goes beyond mere packet routing.

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   It may be desirable to encode a pointers to function and its
   function-arguments within an MPLS packet transport header.  For
   example, in MPLS we can encode the FUNC::ARGs within the label stack
   or after the bottom of stack to support the equivalent of FUNC::ARG
   in SRv6 as described in [RFC8986].

2.6.  Application Aware Networking (APN)

   Application-aware Networking (APN) allows application-aware
   information (i.e., APN attribute) including APN identification (ID)
   and/or APN parameters (e.g. network performance requirements) to be
   encapsulated at network edge devices and carried in packets
   traversing an APN domain in order to facilitate service provisioning,
   perform fine-granularity traffic steering and network resource
   adjustment.  To support APN in MPLS networks, mechanisms are needed
   to hold the APN attribute.

3.  Co-existence of Usecases

   Two or more of the aforementioned use cases MAY co-exist in the same
   packet.  Some examples of such usecases are described below.

3.1.  IOAM with Network Slicing

   IOAM may provide key functions with network slicing to help ensure
   that critical network slice SLOs are being met by the network

   In such a case, IOAM is able collect key performance measurement
   parameters of network slice traffic flows as it traverses the
   transport network.

   This may require, in addition to carrying a specific network slice
   selector (e.g., GISS), the MPLS network slice packets may have to
   also carry IOAM ancillary data.

   Note that the IOAM ancillary data may have to be modified, and
   updated on some/all LSRs traversed by the network slice MPLS packets.

3.2.  IOAM with Time Sensitive Networking

   IOAM operation may also be desirable on MPLS packets that carry time-
   sensitive related data.  Similarly, this may require the presence of
   multiple ancillary data (whether In-stack or Post-stack ancillary
   data) to be present in the same MPLS packet.

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4.  IANA Considerations

   This document has no IANA actions.

5.  Security Considerations

   This document introduces no new security considerations.

6.  Acknowledgement

   The authors gratefully acknowledge the input of the members of the
   MPLS Open Design Team.

7.  Contributors

   The following individuals contributed to this document:

      Kiran Makhijani
      Futurewei Technologies

      Haoyu Song
      Futurewei Technologies

      Loa Andersson
      Bronze Dragon Consulting

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

8.2.  Informative References

              Saad, T., Beeram, V. P., Wen, B., Ceccarelli, D., Halpern,
              J., Peng, S., Chen, R., Liu, X., Contreras, L. M., Rokui,
              R., and L. Jalil, "Realizing Network Slices in IP/MPLS

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              Networks", Work in Progress, Internet-Draft, draft-
              bestbar-teas-ns-packet-06, 22 December 2021,

              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-02, 6 August 2021,

              Gandhi, R., Ali, Z., Brockners, F., Wen, B., Decraene, B.,
              and V. Kozak, "MPLS Data Plane Encapsulation for In-situ
              OAM Data", Work in Progress, Internet-Draft, draft-gandhi-
              mpls-ioam-01, 9 September 2021,

              Gandhi, R., Ali, Z., Filsfils, C., Brockners, F., Wen, B.,
              and V. Kozak, "MPLS Data Plane Encapsulation for In-situ
              OAM Data", Work in Progress, Internet-Draft, draft-gandhi-
              mpls-ioam-sr-06, 18 February 2021,

              Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
              for In-situ OAM", Work in Progress, Internet-Draft, draft-
              ietf-ippm-ioam-data-17, 13 December 2021,

              Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
              Z., and F. Clad, "Introducing Resource Awareness to SR
              Segments", Work in Progress, Internet-Draft, draft-ietf-
              spring-resource-aware-segments-03, 12 July 2021,

              Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L. M., and J. Tantsura,

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              "Framework for IETF Network Slices", Work in Progress,
              Internet-Draft, draft-ietf-teas-ietf-network-slices-05, 25
              October 2021, <

              Kompella, K., Beeram, V. P., Saad, T., and I. Meilik,
              "Multi-purpose Special Purpose Label for Forwarding
              Actions", Work in Progress, Internet-Draft, draft-
              kompella-mpls-mspl4fa-01, 12 July 2021,

              Li, Z. and J. Dong, "Carrying Virtual Transport Network
              Identifier in MPLS Packet", Work in Progress, Internet-
              Draft, draft-li-mpls-enhanced-vpn-vtn-id-01, 14 April
              2021, <

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,

   [RFC8596]  Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
              "MPLS Transport Encapsulation for the Service Function
              Chaining (SFC) Network Service Header (NSH)", RFC 8596,
              DOI 10.17487/RFC8596, June 2019,

   [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,

Authors' Addresses

   Tarek Saad
   Juniper Networks


   Kiran Makhijani
   Futurewei Technologies

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   Haoyu Song
   Futurewei Technologies


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