Internet Engineering Task Force (IETF)                     B. Varga, Ed.
Request for Comments: 9025                                     J. Farkas
Category: Standards Track                                       Ericsson
ISSN: 2070-1721                                                L. Berger
                                                 LabN Consulting, L.L.C.
                                                                A. Malis
                                                        Malis Consulting
                                                               S. Bryant
                                                  Futurewei Technologies
                                                              April 2021

     Deterministic Networking (DetNet) Data Plane: MPLS over UDP/IP


   This document specifies the MPLS Deterministic Networking (DetNet)
   data plane operation and encapsulation over an IP network.  The
   approach is based on the operation of MPLS-over-UDP technology.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Table of Contents

   1.  Introduction
   2.  Terminology
     2.1.  Terms Used in This Document
     2.2.  Abbreviations
     2.3.  Requirements Language
   3.  DetNet MPLS Operation over DetNet IP PSNs
   4.  DetNet Data Plane Procedures
   5.  Management and Control Information Summary
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Authors' Addresses

1.  Introduction

   Deterministic Networking (DetNet) is a service that can be offered by
   a network to DetNet flows.  DetNet provides these flows extremely low
   packet loss rates and assured maximum end-to-end delivery latency.
   General background and concepts of DetNet can be found in [RFC8655].

   To carry DetNet MPLS flows with full functionality at the DetNet
   layer over an IP network, the following components are required
   (these are a subset of the requirements for MPLS encapsulation listed
   in [RFC8964]):

   1.  A method for identifying DetNet flows to the processing element.

   2.  A method for carrying the DetNet sequence number.

   3.  A method for distinguishing DetNet Operations, Administration,
       and Maintenance (OAM) packets from DetNet data packets.

   4.  A method for carrying queuing and forwarding indication.

   These requirements are satisfied by the DetNet over MPLS
   Encapsulation described in [RFC8964] and they are partly satisfied
   (i.e., IP flows can be identified; however, no DetNet sequence number
   is carried) by the DetNet IP data plane defined in [RFC8939].

   This document specifies use of the MPLS DetNet encapsulation over an
   IP network.  The approach is modeled on the operation of MPLS over an
   IP Packet Switched Network (PSN) using UDP encapsulation [RFC7510].
   It maps the MPLS data plane encapsulation described in [RFC8964] to
   the DetNet IP data plane defined in [RFC8939].

   [RFC7510] specifies that "MPLS-in-UDP MUST NOT be used over the
   general Internet, or over non-cooperating network operators, to carry
   traffic that is not congestion controlled."  This constraint does
   apply to the use of RFC 7510 in a DetNet network because DetNet is
   constrained to operate within a single administrative control or
   within a closed group of administrative control.

2.  Terminology

2.1.  Terms Used in This Document

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

2.2.  Abbreviations

   The following abbreviations are used in this document:

   d-CW          A DetNet Control Word (d-CW) is used for sequencing and
                 identifying duplicate packets of a DetNet flow at the
                 DetNet service sub-layer.

   DetNet        Deterministic Networking

   DSCP          Differentiated Services Code Point

   A-Label       A special case of an S-Label, whose properties are
                 known only at the aggregation and deaggregation

   F-Label       A DetNet "forwarding" label that identifies the LSP
                 used to forward a DetNet flow across an MPLS PSN, e.g.,
                 a hop-by-hop label used between label-switching

   MPLS          Multiprotocol Label Switching

   OAM           Operations, Administration, and Maintenance

   PEF           Packet Elimination Function

   POF           Packet Ordering Function

   PREOF         Packet Replication, Elimination, and Ordering Functions

   PRF           Packet Replication Function

   PSN           Packet Switched Network

   S-Label       A DetNet "service" label that is used between DetNet
                 nodes that also implement the DetNet service sub-layer
                 functions.  An S-Label is also used to identify a
                 DetNet flow at the DetNet service sub-layer.

2.3.  Requirements Language

   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.

3.  DetNet MPLS Operation over DetNet IP PSNs

   This document builds on the specification of MPLS over UDP defined in
   [RFC7510].  It may partly or entirely replace the F-Label(s) used in
   [RFC8964] with UDP and IP headers.  The UDP and IP header information
   is used to identify DetNet flows, including member flows, per
   [RFC8939].  The resulting encapsulation is shown in Figure 1.  There
   may be zero or more F-Labels between the S-Label and the UDP header.

   Note that this encapsulation works equally well with IPv4, IPv6, and
   IPv6-based Segment Routing [RFC8754].

      |                                 |
      |         DetNet App-Flow         |
      |         Payload  Packet         |
      |                                 |
      +---------------------------------+ <--\
      |       DetNet Control Word       |    |
      +---------------------------------+    +--> DetNet data plane
      |             S-Label             |    |    MPLS encapsulation
      +---------------------------------+    |
      |          [ F-Label(s) ]         |    |
      +---------------------------------+ <--+
      |           UDP Header            |    |
      +---------------------------------+    +--> DetNet data plane
      |           IP Header             |    |    IP encapsulation
      +---------------------------------+ <--/
      |           Data-Link             |
      |           Physical              |

               Figure 1: UDP/IP Encapsulation of DetNet MPLS

   S-Labels, A-Labels (when present), d-CW, and zero or more F-Labels
   are used as defined in [RFC8964] and are not modified by this

4.  DetNet Data Plane Procedures

   To support outgoing DetNet MPLS over UDP encapsulation, an
   implementation MUST support the provisioning of UDP and IP header
   information in addition to or in place of F-Label(s).  Note, when the
   PRF is performed at the MPLS service sub-layer, there will be
   multiple member flows, and each member flow will require the
   provisioning of their own UDP and IP header information.  The headers
   for each outgoing packet MUST be formatted according to the
   configuration information and as defined in [RFC7510], and the UDP
   Source Port value MUST be set to uniquely identify the DetNet flow.
   The packet MUST then be handled as a DetNet IP packet, per [RFC8939].
   This includes QoS-related traffic treatment.

   To support the receive processing defined in this document, an
   implementation MUST also support the provisioning of received UDP and
   IP header information.  The provisioned information MUST be used to
   identify incoming app flows based on the combination of S-Label and
   incoming encapsulation header information.  Normal receive processing
   as defined in [RFC8964], including PEF and POF, can then take place.

5.  Management and Control Information Summary

   The following summarizes the minimum set of information that is
   needed to configure DetNet MPLS over UDP/IP:

   *  Label information (A-Labels, S-Labels, and F-Labels) to be mapped
      to UDP/IP flows.  Note that, for example, a single S-Label can map
      to multiple sets of UDP/IP information when PREOF is used.

   *  IPv4 or IPv6 source address field

   *  IPv4 or IPv6 destination address field

   *  DSCP Field in either IPv4 Type of Service or IPv6 Traffic Class

   *  UDP Source Port

   *  UDP Destination Port

   *  Use/non-use of UDP checksum

   This information MUST be provisioned per DetNet flow via
   configuration, e.g., via the controller [RFC8655] or management
   plane.  Not using the UDP checksum has to be evaluated on a case-by-
   case basis for a given network scenario based on the exception
   criteria defined in [RFC7510], particularly when IPv6 is used.

   It is the responsibility of the DetNet Controller Plane to properly
   provision both flow identification information and the flow-specific
   resources needed to provide the traffic treatment needed to meet each
   flow's service requirements.  This applies for both aggregated and
   individual flows.

      |  Note: In the presence of network (and port) address translation
      |  devices/functions, it would be up to the Controller Plane to
      |  determine the appropriate information to ensure proper mapping
      |  at the sender/receiver.

6.  Security Considerations

   The solution defined in this document reuses mechanisms specified in
   other documents, and the security considerations in those documents
   apply equally to this document.  Of particular note is [RFC7510], as
   this document is primarily an application of MPLS-over-UDP.
   Additionally, the security considerations of DetNet in general are
   discussed in [RFC8655] and [DETNET-SECURITY].  Finally, MPLS- and IP-
   specific security considerations are described in [RFC8964] and
   [RFC8939].  This document does not have additional security

7.  IANA Considerations

   This document has no IANA actions.

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,

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,

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

   [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,

   [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, <>.

8.2.  Informative References

              Grossman, E., Ed., Mizrahi, T., and A. J. Hacker,
              "Deterministic Networking (DetNet) Security
              Considerations", Work in Progress, Internet-Draft, draft-
              ietf-detnet-security-16, 22 February 2021,

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

   [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,


   The authors wish to thank Pat Thaler, Norman Finn, Loa Anderson,
   David Black, Rodney Cummings, Ethan Grossman, Tal Mizrahi, David
   Mozes, Craig Gunther, George Swallow, Yuanlong Jiang, and Carlos
   J. Bernardos for their various contributions to this work.


   This document is derived from an earlier draft that was edited by
   Jouni Korhonen (, and as such, he contributed
   to and authored text in this document.

Authors' Addresses

   Balázs Varga (editor)
   Magyar Tudosok krt. 11.


   János Farkas
   Magyar Tudosok krt. 11.


   Lou Berger
   LabN Consulting, L.L.C.


   Andrew G. Malis
   Malis Consulting


   Stewart Bryant
   Futurewei Technologies