MPLS Working Group                                               T. Saad
Internet-Draft                                          Juniper Networks
Intended status: Informational                              K. Makhijani
Expires: 20 November 2022                                        H. Song
                                                  Futurewei Technologies
                                                               G. Mirsky
                                                                Ericsson
                                                             19 May 2022


  Use Cases for MPLS Network Action Indicators and MPLS Ancillary Data
                    draft-ietf-mpls-mna-usecases-00

Abstract

   This document presents a number of use cases that have a common need
   for encoding network action indicators and associated ancillary data
   inside MPLS packets.  There has been significant recent interest in
   extending the MPLS data plane to carry such indicators and ancillary
   data to address a number of use cases that are described in this
   document.

   The use cases described in this document are not an exhaustive set,
   but rather the ones that are actively discussed by members of the
   IETF MPLS, PALS and DETNET working groups participating in the MPLS
   Open Design Team.

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
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on 20 November 2022.

Copyright Notice

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



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   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 carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Acronyms and Abbreviations  . . . . . . . . . . . . . . .   3
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  No Further Fastreroute  . . . . . . . . . . . . . . . . .   3
     2.2.  In-situ OAM . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Network Slicing . . . . . . . . . . . . . . . . . . . . .   4
       2.3.1.  Global Identifier as Flow-Aggregate Selector  . . . .   5
       2.3.2.  Forwarding Label as a Flow-Aggregate Selector . . . .   6
     2.4.  Delay Budgets for Time-Bound Applications . . . . . . . .   6
       2.4.1.  Stack Based Methods for Latency Control . . . . . . .   7
     2.5.  NSH-based Service Function Chaining . . . . . . . . . . .   7
     2.6.  Network Programming . . . . . . . . . . . . . . . . . . .   7
     2.7.  Application Aware Networking  . . . . . . . . . . . . . .   8
   3.  Co-existence of Usecases  . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   This document describes important cases that require carrying
   additional ancillary data within the MPLS packets, as well as means
   to indicate the ancillary data is present, and a specific action
   needs to be performed on the packet.

   These use cases have been identified by the MPLS Working Group Open
   Design Team working on defining MPLS Network Actions for the MPLS
   data plane.  The MPLS Ancillary Data (AD) can be classified as:

   *  implicit, or "no-data" associated with a Network Action (NA)
      indicator,





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   *  residing within the MPLS label stack and referred to as In Stack
      Data (ISD), and

   *  residing after the Bottom of MPLS label Stack (BoS) and referred
      to as Post Stack Data (PSD).

   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.

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
      [I-D.ietf-teas-ietf-network-slices].

   Time-Bound Networking:
      Networks that transport time-bounded traffic.

1.2.  Acronyms and Abbreviations

      ISD: In-stack data

      PSD: Post-stack data

      MNA: MPLS Network Action

      NAI: Network Action Indicator

      AD: Ancillary Data

2.  Use Cases

2.1.  No Further Fastreroute

   MPLS Fast Reroute (FRR) [RFC4090], [RFC5286] and [RFC7490] is a
   useful and widely deployed tool for minimizing packet loss in the
   case of a link or node failure.

   Several cases exist where, once FRR has taken place in an MPLS
   network and resulted in rerouting a packet away from the failure, a
   second FRR that impacts the same packet to rerouting is not helpful,
   and may even be disruptive.



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   For example, in such a case, the packet may continue to loop until
   its TTL expires.  This can lead to link congestion and further packet
   loss.  Thus, the attempt to prevent a packet from being dropped may
   instead affect many other packets.  A proposal to address this is
   presented in [I-D.kompella-mpls-nffrr].

2.2.  In-situ OAM

   In-situ Operations, Administration, and Maintenance (IOAM) may record
   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
   (PM).

   IOAM can run in two modes Edge-to-Edge (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 IOAM-capable 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).

   The IOAM data may be added after the bottom of the MPLS 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 the
   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.  In HbH IOAM mode, nodes that
   are capable of processing IOAM will intercept and process the IOAM
   data accordingly.  The presence of IOAM header and optional IOAM data
   will betransparent to nodes that do not support or do not participate
   in the IOAM process.

2.3.  Network Slicing

   [I-D.ietf-teas-ietf-network-slices] specifies the definition of an
   IETF Network Slice.  It further discusses the general framework for
   requesting and operating IETF Network Slices, their characteristics,
   and the necessary system components and interfaces.




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   Multiple network slices can be realized on top of a single physical
   network.

   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.

   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 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 Slice Level Objectives (SLOs) are
       being met.  This may be done by active measurements (inferred) or
       by using hybrid measurement methods, e.g., 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.

2.3.1.  Global Identifier as Flow-Aggregate Selector

   A Global Identifier as a Flow-Aggregate Selector (G-FAS) can be
   encoded in the MPLS packet as defined in [I-D.kompella-mpls-mspl4fa],
   [I-D.li-mpls-enhanced-vpn-vtn-id], and
   [I-D.decraene-mpls-slid-encoded-entropy-label-id].  The G-FAS is used
   to associate the packets belonging to Slice-Flow Aggregate to the
   underlying Network Resource Partition (NRP) as described in
   [I-D.bestbar-teas-ns-packet].



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   The G-FAS can be encoded within an MPLS label carried in the packet's
   MPLS label stack.  All packets that belong to the same flow aggregate
   MAY carry the same FAS in the MPLS label stack.

   When MPLS packets carry a G-FAS, MPLS LSRs use the forwarding label
   to select the forwarding next-hop(s), and use the G-FAS in the MPLS
   packet to infer the specific forwarding treatment that needs to be
   applied on the packet.

2.3.2.  Forwarding Label as a Flow-Aggregate 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
   service"'.

   It is possible by assigning a unique MPLS forwarding label to each
   flow aggregate (FEC) to distinguish the packets forwarded to the same
   destination. from other flow 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.

2.4.  Delay Budgets for Time-Bound Applications

   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).  IEEE-802.1 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 a bounded end-to-end latency but does not
   influence the queueing of individual packets in each router along
   that path.

   When carried over the MPLS data plane, a solution is required to
   enable the delivery of such packets that can be delivered to their
   final destination by a given time budget.






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2.4.1.  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
   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-bound 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
   as ISD or after BoS as PSD).

2.5.  NSH-based Service Function Chaining

   [RFC8595] describes how Service Function Chaining (SFC) can be
   realized in an MPLS network by emulating the NSH by using only MPLS
   label stack elements.

   The approach in [RFC8595] introduces some limitations that are
   discussed in [I-D.lm-mpls-sfc-path-verification].  This approach,
   however, can benefit from the framework introduced with MNA
   [I-D.andersson-mpls-mna-fwk].

   For example, it may be possible to extend NSH emulation using MPLS
   labels [RFC8595] to support the functionality of NSH Context Headers,
   whether fixed or variable-length.  One of the use cases could support
   Flow ID [I-D.ietf-sfc-nsh-tlv] that may be used for load-balancing
   among Service Function Forwarders (SFFs) and/or the Service Function
   (SF) within the same SFP.

2.6.  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.



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

   It may be desirable to encode a pointer to function and its 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].

2.7.  Application Aware Networking

   Application-aware Networking (APN) as described in
   [I-D.li-apn-problem-statement-usecases] allows application-aware
   information (i.e., APN attributes) 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.

   The APN data is carried in packets to facilitate service
   provisioning, and be used to perform fine-granularity traffic
   steering and network resource adjustment.  To support APN in MPLS
   networks, mechanisms are needed to carry such APN data in MPLS
   encapsulated packets.

3.  Co-existence of Usecases

   Two or more of the aforementioned use cases MAY co-exist in the same
   packet.  This may require the presence of multiple ancilary data
   (whether In-stack or Post-stack ancillary data) to be present in the
   same MPLS packet.

   For example, IOAM may provide key functions along with network
   slicing to help ensure that critical network slice SLOs are being met
   by the network provider.  In this case, IOAM is able to collect key
   performance measurement parameters of network slice traffic flows as
   it traverses the transport network.

4.  IANA Considerations

   This document has no IANA actions.

5.  Security Considerations

   This document introduces no new security considerations.







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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:

      Loa Andersson
      Bronze Dragon Consulting
      Email: loa@pi.nu

8.  Informative References

   [I-D.andersson-mpls-mna-fwk]
              Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
              Network Actions Framework", Work in Progress, Internet-
              Draft, draft-andersson-mpls-mna-fwk-01, 27 April 2022,
              <https://www.ietf.org/archive/id/draft-andersson-mpls-mna-
              fwk-01.txt>.

   [I-D.bestbar-teas-ns-packet]
              Saad, T., Beeram, V. P., Dong, J., 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 Networks", Work in Progress, Internet-Draft,
              draft-bestbar-teas-ns-packet-10, 5 May 2022,
              <https://www.ietf.org/archive/id/draft-bestbar-teas-ns-
              packet-10.txt>.

   [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-03, 11 February 2022,
              <https://www.ietf.org/archive/id/draft-decraene-mpls-slid-
              encoded-entropy-label-id-03.txt>.

   [I-D.gandhi-mpls-ioam]
              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-04, 2 March 2022,
              <https://www.ietf.org/archive/id/draft-gandhi-mpls-ioam-
              04.txt>.




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   [I-D.gandhi-mpls-ioam-sr]
              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,
              <https://www.ietf.org/archive/id/draft-gandhi-mpls-ioam-
              sr-06.txt>.

   [I-D.ietf-ippm-ioam-data]
              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,
              <https://www.ietf.org/archive/id/draft-ietf-ippm-ioam-
              data-17.txt>.

   [I-D.ietf-sfc-nsh-tlv]
              Wei, Y., Elzur, U., Majee, S., Pignataro, C., and D. E.
              Eastlake, "Network Service Header (NSH) Metadata Type 2
              Variable-Length Context Headers", Work in Progress,
              Internet-Draft, draft-ietf-sfc-nsh-tlv-15, 20 April 2022,
              <https://www.ietf.org/archive/id/draft-ietf-sfc-nsh-tlv-
              15.txt>.

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "Framework for IETF
              Network Slices", Work in Progress, Internet-Draft, draft-
              ietf-teas-ietf-network-slices-10, 27 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
              network-slices-10.txt>.

   [I-D.kompella-mpls-mspl4fa]
              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-02, 9 February 2022,
              <https://www.ietf.org/archive/id/draft-kompella-mpls-
              mspl4fa-02.txt>.

   [I-D.kompella-mpls-nffrr]
              Kompella, K. and W. Lin, "No Further Fast Reroute", Work
              in Progress, Internet-Draft, draft-kompella-mpls-nffrr-02,
              12 July 2021, <https://www.ietf.org/archive/id/draft-
              kompella-mpls-nffrr-02.txt>.

   [I-D.li-apn-problem-statement-usecases]
              Li, Z., Peng, S., Voyer, D., Xie, C., Liu, P., Qin, Z.,
              and G. Mishra, "Problem Statement and Use Cases of



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              Application-aware Networking (APN)", Work in Progress,
              Internet-Draft, draft-li-apn-problem-statement-usecases-
              06, 7 March 2022, <https://www.ietf.org/archive/id/draft-
              li-apn-problem-statement-usecases-06.txt>.

   [I-D.li-mpls-enhanced-vpn-vtn-id]
              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-02, 7 March 2022,
              <https://www.ietf.org/archive/id/draft-li-mpls-enhanced-
              vpn-vtn-id-02.txt>.

   [I-D.lm-mpls-sfc-path-verification]
              Yao, L. and G. Mirsky, "MPLS-based Service Function
              Path(SFP) Consistency Verification", Work in Progress,
              Internet-Draft, draft-lm-mpls-sfc-path-verification-02, 21
              February 2021, <https://www.ietf.org/archive/id/draft-lm-
              mpls-sfc-path-verification-02.txt>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <https://www.rfc-editor.org/info/rfc4090>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,
              <https://www.rfc-editor.org/info/rfc7490>.

   [RFC8595]  Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
              Forwarding Plane for Service Function Chaining", RFC 8595,
              DOI 10.17487/RFC8595, June 2019,
              <https://www.rfc-editor.org/info/rfc8595>.








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   [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>.

Authors' Addresses

   Tarek Saad
   Juniper Networks
   Email: tsaad@juniper.net


   Kiran Makhijani
   Futurewei Technologies
   Email: kiranm@futurewei.com


   Haoyu Song
   Futurewei Technologies
   Email: haoyu.song@futurewei.com


   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

























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