Deterministic Networking (DetNet): DetNet PREOF via MPLS over UDP/IP
draft-ietf-detnet-mpls-over-ip-preof-11

DetNet                                                          B. Varga
Internet-Draft                                                 J. Farkas
Intended status: Informational                                  Ericsson
Expires: 25 August 2024                                         A. Malis
                                                        Malis Consulting
                                                        22 February 2024

  Deterministic Networking (DetNet): DetNet PREOF via MPLS over UDP/IP
                draft-ietf-detnet-mpls-over-ip-preof-11

Abstract

   This document describes how DetNet IP data plane can support the
   Packet Replication, Elimination, and Ordering Functions (PREOF) built
   on the existing MPLS PREOF solution defined for DetNet MPLS Data
   Plane and the mechanisms defined by MPLS-over-UDP technology.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Terms Used in This Document . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements for adding PREOF to DetNet IP  . . . . . . . . .   4
   4.  Adding PREOF to DetNet IP . . . . . . . . . . . . . . . . . .   4
     4.1.  Solution Basics . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Encapsulation . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Packet Processing . . . . . . . . . . . . . . . . . . . .   5
     4.4.  Flow Aggregation  . . . . . . . . . . . . . . . . . . . .   6
     4.5.  PREOF Processing  . . . . . . . . . . . . . . . . . . . .   7
     4.6.  PREOF capable DetNet IP domain  . . . . . . . . . . . . .   8
   5.  Control and Management Plane Parameters . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The DetNet Working Group has defined Packet Replication (PRF), Packet
   Elimination (PEF) and Packet Ordering (POF) functions (represented as
   PREOF) to provide service protection by the DetNet service sub-layer
   [RFC8655].  The PREOF service protection method relies on copies of
   the same packet sent over multiple maximally disjoint paths and uses
   sequencing information to eliminate duplicates.  A possible
   implementation of the PRF and PEF functions is described in
   [IEEE8021CB] and the related YANG data model is defined in
   [IEEEP8021CBcv].  A possible implementation of the POF function is
   described in [I-D.ietf-detnet-pof].  Figure 1 shows a DetNet flow on
   which PREOF functions are applied during forwarding from the source
   to the destination.

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                                          +------------+
                +---------------E1---+    |            |
    +---+       |               |    +---R3---+        |          +---+
    |src|------R1           +---+             |        E3----O----+dst|
    +---+       |           |                 E2-------+          +---+
                +----------R2                 |
                            +-----------------+

    R: replication function (PRF)
    E: elimination function (PEF)
    O: ordering function (POF)

                Figure 1: PREOF scenario in a DetNet network

   In general, the use of PREOF functions require sequencing information
   to be included in the packets of a DetNet compound flow.  This can be
   done by adding a sequence number or time stamp as part of DetNet
   encapsulation.  Sequencing information is typically added once, at or
   close to the source.

   The DetNet MPLS data plane [RFC8964] specifies how sequencing
   information is encoded in the MPLS header.  However, the DetNet IP
   data plane described in [RFC8939] does not specify how sequencing
   information can be encoded in the IP packet.  This document provides
   sequencing information to DetNet IP nodes, so it results in an
   improved version of the DetNet IP data plane.  As suggested by
   [RFC8938], the solution uses existing standardized headers and
   encapsulations.  The improvement is achieved by re-using the DetNet
   MPLS over UDP/IP data plane [RFC9025] with the restriction of using
   zero F-labels.

2.  Terminology

2.1.  Terms Used in This Document

   This document uses the terminology established in the DetNet
   architecture [RFC8655], and the reader is assumed to be familiar with
   that document and its terminology.

2.2.  Abbreviations

   The following abbreviations are used in this document:

   DetNet        Deterministic Networking.

   PEF           Packet Elimination Function.

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   POF           Packet Ordering Function.

   PREOF         Packet Replication, Elimination and Ordering Functions.

   PRF           Packet Replication Function.

3.  Requirements for adding PREOF to DetNet IP

   The requirements for adding PREOF to DetNet IP are:

   *  to reuse existing DetNet data plane solutions (e.g., [RFC8964],
      [RFC9025]).

   *  to allow the DetNet service sub-layer for IP packet switched
      networks with minimal implementation effort.

   The described solution practically gains from MPLS header fields
   without requiring the support of the MPLS forwarding plane.

4.  Adding PREOF to DetNet IP

4.1.  Solution Basics

   The DetNet IP encapsulation supporting DetNet Service sub-layer is
   based on the "UDP tunneling" concept.  The solution creates a set of
   underlay UDP/IP tunnels between an overlay set of DetNet relay nodes.

   At the edge of a PREOF capable DetNet IP domain the DetNet flow is
   encapsulated in an UDP packet containing the sequence number used by
   PREOF functions within the domain.  This solution maintains the 6-
   tuple-based DetNet flow identification in DetNet transit nodes, which
   operate at the DetNet forwarding sub-layer between the DetNet service
   sub-layer nodes; therefore, it is compatible with [RFC8939].
   Figure 2 shows how the PREOF capable DetNet IP data plane fits into
   the DetNet sub-layers.

                    DetNet          IP
                       .
                       .
                 +------------+
                 |  Service   | d-CW, Service-ID (S-label)
                 +------------+
                 | Forwarding | UDP/IP Header
                 +------------+

                                *d-CW: DetNet Control Word

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                Figure 2: PREOF capable DetNet IP data plane

4.2.  Encapsulation

   The PREOF capable DetNet IP encapsulation builds on encapsulating
   DetNet PseudoWire (PW) directly over UDP.  That is, it combines
   DetNet MPLS [RFC8964] with DetNet MPLS-in-UDP [RFC9025], without
   using any F-Labels as shown in Figure 3.  DetNet flows are identified
   at the receiving DetNet service sub-layer processing node via the
   S-Label and/or the UDP/IP header information.  Sequencing information
   for PREOF is provided by the DetNet Control Word (d-CW) as per
   [RFC8964].  The S-label is used to identify both the DetNet flow and
   the DetNet App-flow type.  The UDP tunnel is used to direct the
   packet across the DetNet domain to the next DetNet service sub-layer
   processing node.

      +---------------------------------+
      |                                 |
      |         DetNet App-Flow         |
      |       (original IP) Packet      |
      |                                 |
      +---------------------------------+ <--\
      |       DetNet Control Word       |    |
      +---------------------------------+    +--> PREOF capable
      |       Service-ID (S-Label)      |    |    DetNet IP data
      +---------------------------------+    |    plane encapsulation
      |            UDP Header           |    |
      +---------------------------------+    |
      |            IP Header            |    |
      +---------------------------------+ <--/
      |            Data-Link            |
      +---------------------------------+
      |             Physical            |
      +---------------------------------+

              Figure 3: PREOF capable DetNet IP encapsulation

4.3.  Packet Processing

   IP ingress and egress nodes of the PREOF capable DetNet IP domain add
   and remove a DetNet service-specific d-CW and Service-ID (i.e.,
   S-Label).  Relay nodes can change Service-ID values when processing a
   DetNet flow, i.e., incoming and outgoing Service-IDs of a DetNet flow
   can be different.  Service-ID values are provisioned per DetNet
   service via configuration, e.g., via the Controller Plane described
   in [RFC8938].  In some PREOF topologies, the node performing

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   replication sends the packets to multiple nodes performing e.g., PEF
   or POF and the replication node can use different Service-ID values
   for the different member flows for the same DetNet service.

   Note, that Service-IDs is a local ID on the receiver side providing
   identification of the DetNet flow at the downstream DetNet service
   sub-layer receiver.

4.4.  Flow Aggregation

   Two methods can be used for flow aggregation:

   *  aggregation using same UDP tunnel,

   *  aggregating DetNet flows as a new DetNet flow.

   In the first case, the different DetNet PseudoWires use the same UDP
   tunnel, so they are treated as a single (aggregated) flow at the
   forwarding sub-layer.  At the service sub-layer, each flow uses a
   different Service ID (see Figure 3 ).

   For the second option, an additional hierarchy is created thanks to
   an additional Service-ID and d-CW tuple added to the encapsulation.
   The Aggregate-ID is a special case of a Service-ID, whose properties
   are known only at the aggregation and de-aggregation end points.  It
   is a property of the Aggregate-ID that it is followed by a d-CW
   followed by a Service-ID/d-CW tuple.  Figure 4 shows the
   encapsulation in case of aggregation.

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      +---------------------------------+
      |                                 |
      |         DetNet App-Flow         |
      |         Payload  Packet         |
      |                                 |
      +---------------------------------+ <--\
      |       DetNet Control Word       |    |
      +---------------------------------+    +--> PREOF capable
      |       Service-ID (S-Label)      |    |    DetNet IP data
      +---------------------------------+    |    plane encapsulation
      |       DetNet Control Word       |    |
      +---------------------------------+    |
      |      Aggregate-ID (A-Label)     |    |
      +---------------------------------+    |
      |           UDP Header            |    |
      +---------------------------------+    |
      |            IP Header            |    |
      +---------------------------------+ <--/
      |            Data-Link            |
      +---------------------------------+
      |             Physical            |
      +---------------------------------+

          Figure 4: Aggregating DetNet flows as a new DetNet flow

   The option used for aggregation is known by configuration of the
   aggregation/de-aggregation nodes.

   If several Detnet flows are aggregated in a single UDP tunnel, they
   all need to follow the same path in the network.

4.5.  PREOF Processing

   A node operating on a received DetNet flow at the DetNet service sub-
   layer uses the local context associated with a received Service-ID to
   determine which local DetNet operation(s) are applied to received
   packet.  A Service-ID can be allocated to be unique and enabling
   DetNet flow identification regardless of which input interface or UDP
   tunnel the packet is received.  It is important to note that Service-
   ID values are driven by the receiver, not the sender.

   The DetNet forwarding sub-layer is supported by the UDP tunnel and is
   responsible for providing resource allocation and explicit routes.

   The outgoing PREOF encapsulation and processing can be implemented
   via the provisioning of UDP and IP header information.  Note, when
   PRF is performed at the DetNet service sub-layer, there are multiple

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   member flows, and each member flow requires their own Service-ID, UDP
   and IP header information.  The headers for each outgoing packet are
   formatted according to the configuration information, and the UDP
   Source Port value is set to uniquely identify the DetNet flow.  The
   packet is then handled as a PREOF capable DetNet IP packet.

   The incoming PREOF processing can be implemented via the provisioning
   of received Service-ID, UDP and IP header information.  The
   provisioned information is used to identify incoming app-flows based
   on the combination of Service-ID and/or incoming encapsulation header
   information.

4.6.  PREOF capable DetNet IP domain

   Figure 5 shows using PREOF in a PREOF capable DetNet IP network,
   where service protection is provided end to end, an not only within
   sub-networks like depicted in Figure 4 of [RFC8939].

             <---------- PREOF capable DetNet IP --------------->
                                       ______
                             ____     /      \__
                  ____      /     \__/          \____________
   +----+      __/    \____/                                 \    +----+
   |src |_____/                                               \___| dst|
   +----+     \_______            DetNet network    __________/   +----+
                      \_______                    _/
                              \         __     __/
                               \_______/  \___/

                                          +------------+
                +---------------E1---+    |            |
   +----+       |               |    +---R3---+        |          +----+
   |src |------R1           +---+             |        E3----O----+ dst|
   +----+       |           |                 E2-------+          +----+
                +----------R2                 |
                            +-----------------+

                  Figure 5: PREOF capable DetNet IP domain

5.  Control and Management Plane Parameters

   The information needed to identify individual and aggregated DetNet
   flows is summarized as follows:

   *  Service-ID information to be mapped to UDP/IP flows.  Note that,
      for example, a single Service-ID can map to multiple sets of UDP/
      IP information when PREOF is used.

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   *  IPv4 or IPv6 source address field.

   *  IPv4 or IPv6 source address prefix length, where a zero (0) value
      effectively means that the address field is ignored.

   *  IPv4 or IPv6 destination address field.

   *  IPv4 or IPv6 destination address prefix length, where a zero (0)
      effectively means that the address field is ignored.

   *  IPv6 flow label field.

   *  IPv4 protocol field being equal to "UDP".

   *  IPv6 (last) next header field being equal to "UDP".

   *  For the IPv4 Type of Service and IPv6 Traffic Class Fields:

      -  Whether or not the DSCP field is used in flow identification as
         the use of the DSCP field for flow identification is optional.

      -  If the DSCP field is used to identify a flow, then the flow
         identification information (for that flow) includes a list of
         DSCPs used by the given DetNet flow.

   *  UDP Source Port.  Support for both exact and wildcard matching is
      required.  Port ranges can optionally be used.

   *  UDP Destination Port.  Support for both exact and wildcard
      matching is required.  Port ranges can optionally be used.

   *  For end systems, an optional maximum IP packet size that should be
      used for that outgoing DetNet IP flow.

   This information is provisioned per DetNet flow via configuration,
   e.g., via the controller plane.

   Ordering of the set of information used to identify an individual
   DetNet flow can, for example, be used to provide a DetNet service for
   a specific UDP flow, with unique Source and Destination Port field
   values, while providing a different service for the aggregate of all
   other flows with that same UDP Destination Port value.

   The minimum set of information for the configuration of the DetNet
   service sub-layer is summarized as follows:

   *  App-flow identification information.

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   *  Sequence number length.

   *  PREOF + related Service-ID(s).

   *  Associated forwarding sub-layer information.

   *  Service aggregation information.

   The minimum set of information for the configuration of the DetNet
   forwarding sub-layer is summarized as follows:

   *  UDP tunnel specific information.

   *  Traffic parameters.

   These parameters are defined in the DetNet Flow and Service
   information model [RFC9016] and the DetNet YANG model.

   Note: this document focuses on the use of MPLS over UDP/IP
   encapsulation throughout an entire DetNet IP network, making MPLS-
   based DetNet OAM techniques applicable [I-D.ietf-detnet-mpls-oam].
   Using the described encapsulation only for a portion of a DetNet IP
   network that handles the PREOF functionality would complicate OAM.

6.  Security Considerations

   There are no new DetNet related security considerations introduced by
   this solution.  Security considerations of DetNet MPLS [RFC8964] and
   DetNet MPLS over UDP/IP [RFC9025] apply.

7.  IANA Considerations

   This document makes no IANA requests.

8.  Acknowledgements

   Authors extend their appreciation to Stewart Bryant, Pascal Thubert,
   David Black, Shirley Yangfan and Greg Mirsky for their insightful
   comments and productive discussion that helped to improve the
   document.

9.  References

9.1.  Normative References

   [I-D.ietf-detnet-mpls-oam]
              Mirsky, G., Chen, M., and B. Varga, "Operations,
              Administration and Maintenance (OAM) for Deterministic

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              Networks (DetNet) with MPLS Data Plane", Work in Progress,
              Internet-Draft, draft-ietf-detnet-mpls-oam-15, 12 January
              2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
              detnet-mpls-oam-15>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.

   [RFC8938]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane
              Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,
              <https://www.rfc-editor.org/info/rfc8938>.

   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
              <https://www.rfc-editor.org/info/rfc8939>.

   [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
              S., and J. Korhonen, "Deterministic Networking (DetNet)
              Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
              2021, <https://www.rfc-editor.org/info/rfc8964>.

   [RFC9016]  Varga, B., Farkas, J., Cummings, R., Jiang, Y., and D.
              Fedyk, "Flow and Service Information Model for
              Deterministic Networking (DetNet)", RFC 9016,
              DOI 10.17487/RFC9016, March 2021,
              <https://www.rfc-editor.org/info/rfc9016>.

   [RFC9025]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              MPLS over UDP/IP", RFC 9025, DOI 10.17487/RFC9025, April
              2021, <https://www.rfc-editor.org/info/rfc9025>.

9.2.  Informative References

   [I-D.ietf-detnet-pof]
              Varga, B., Farkas, J., Kehrer, S., and T. Heer,
              "Deterministic Networking (DetNet): Packet Ordering
              Function", Work in Progress, Internet-Draft, draft-ietf-
              detnet-pof-11, 15 January 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-detnet-
              pof-11>.

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   [IEEE8021CB]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Frame Replication and Elimination for
              Reliability", DOI 10.1109/IEEESTD.2017.8091139, October
              2017,
              <https://standards.ieee.org/standard/802_1CB-2017.html>.

   [IEEEP8021CBcv]
              Kehrer, S., "FRER YANG Data Model and Management
              Information Base Module", IEEE P802.1CBcv
              /D1.2 P802.1CBcv, March 2021,
              <https://www.ieee802.org/1/files/private/cv-drafts/d1/802-
              1CBcv-d1-2.pdf>.

Authors' Addresses

   Balazs Varga
   Ericsson
   Budapest
   Magyar Tudosok krt. 11.
   1117
   Hungary
   Email: balazs.a.varga@ericsson.com

   Janos Farkas
   Ericsson
   Budapest
   Magyar Tudosok krt. 11.
   1117
   Hungary
   Email: janos.farkas@ericsson.com

   Andrew G. Malis
   Malis Consulting
   Email: agmalis@gmail.com

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