



Network                                                     Shaofu. Peng
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                        23 December 2025
Expires: 26 June 2026


                          Control Word Option
                      draft-peng-6man-cw-option-00

Abstract

   This document introduces new IPv6 options for DOH, to carry flow
   identifier, sequence number, and other customer service mapped
   information that is encapsulated by the provider network, to support
   flow-specific treatment, such as statistics, monitoring, QoS,
   redundancy elimination and reordering, etc.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Control Word Option . . . . . . . . . . . . . . . . . . . . .   3
   3.  Encapsulation of CW Options On Ingress Node . . . . . . . . .   4
   4.  Operations of CW Options On Destination . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [RFC4385] defines Pseudowire Emulation Edge-to-Edge (PWE3) Control
   Word for use over an MPLS packet switched network (PSN).  It
   explicitly indicate that the payload behind the MPLS label stack is
   non-IP, to avoid intermediate nodes always treating payload as IP
   payload, e.g., in the case of hash function in a load distribution
   scheme.  PW MPLS Control Word (PWMCW) is used to encapsulate PW data
   packets.  PW label is used for flow identification.  PWMCW includes
   Sequence Number field for out of order checking and reordering
   functions, that is suitable for circuits sensitive to packet out of
   order, such as Time Division Multiplexed (TDM) circuits.  [RFC8964]
   also defines DetNet Control Word (d-CW) in MPLS data plane.  S-label
   is used for flow identification. d-CW includes Sequence Number field
   for out of order checking and reordering functions for DetNet flows.
   The reason for out of order is multi-path transmission, which may be
   intentional path planning or forced path switching during network
   failures.

   Some provider networks are migrating from MPLS to IPv6.  Customer
   services (including out of order sensitive services) will be
   uniformly encapsulated in IPv6.  The customer services may not be
   aware of this migrating.  However, the service requirement should be
   smoothly met.  The current IPv6 standards lack a unified
   encapsulation method for the identification and sequence number of
   original customer flows.  Although, an IPv6 flow can be typically
   identified by 5-tuple (source address, destination address, source
   port, destination port, and the transport protocol type), some of
   these fields may be unavailable due to either fragmentation or
   encryption, or locating them past a chain of IPv6 extension headers
   may be inefficient.  [RFC6437] defines Flow Label, which, combined
   with Source Address and Destination Address fields, is a more
   efficient IPv6 flow classification.  However, the purpose of flow
   classification is often to obtain specific treatment from the
   provider network, instead of a discriminator for the original



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   customer flows.  Multiple customer flows may encapsulate the same
   Flow Label.  [RFC9343] defines the AltMark option, which includes
   FlowMonID field to identify the monitored flow, but without enough
   space to define the sequence number.  [RFC9566] defines MPLS based
   d-CW over IPv6, which is high cost and requires the IPv6 data plane
   to support additional MPLS forwarding logic beyond pure IPv6
   forwarding.

   This document defines Conctrol Word option in Destination Options
   Header that includes flow identity, sequence number, and other
   customer service mapped information to facilitate support for flow-
   specific treatment, such as statistics, monitoring, QoS, redundancy
   elimination and reordering, etc.

1.1.  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.

2.  Control Word Option


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Option Type  |  Opt Data Len |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Originator                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Flow Identity                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Sequence Number                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Reserved                             ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                  Figure 1

   Option Type: 8-bit identifier of the type of option.  Value TBD by
   IANA; the highest-order 3 bits of thie field is 001 to skip over this
   option and continue processing the header if the processing IPv6 node
   does not recognize the Option Type and to permit the Option Data to
   be changed en route to the packet's final destination.





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   Opt Data Len: 8-bit unsigned integer.  Length of the Option Data
   field of this option, in octets.  It is variable, may set to 12, or
   other larger values if the Reserved field has been defined in future.

   Originator: 32-bit identifier of the originator that specify control
   word for the customer flow.  In general, the originator is the flow
   entrance node.  Note that some intentionally defined forwarding
   methods may frequently remove and add IPv6 header, resulting in the
   Source Address field no longer containing the original source address
   (i.e., the address of the flow entrance node).

   Flow Identity: 32-bit identifier of the customer flow, allocated by
   the originator.  It is used to mark packets of a given flow.  The
   value of zero is to indicate unmarked packets.

   Sequence Number: 32-bit unsigned integer, represents the sequence
   number of a packet in a flow, increasing by 1 with each newly sent
   packet of the same flow.  The circular unsigned 32-bit number space
   excludes the value zero.

   Reserved: If Opt Data Len is set to 12, the Reserved field does not
   exist.  The actual length of field Reserved is equal to Opt Data Len
   minus 12.

3.  Encapsulation of CW Options On Ingress Node

   The flow entrance node, when encapsulating the customer flow with an
   outer IPv6 header, can explicitly insert a DOH contains CW option in
   the outer IPv6 header according to the flow states.  The DOH must be
   inserted before the Routing Header (RH), if RH also needs to be
   inserted.

   The flow entrance node can use local algorithm to assign different
   flow identities to different customer flows.  The algorithm can check
   the 5-tuple of the customer flow to ensure that the generated flow
   identity value has local uniqueness.  Although flow aggregation can
   map multiple flows to the same traffic class, it is still recommended
   to assign different flow identities to these member flows.

   For a given cutomer flow, the sequence number assigned to the first
   received packet is 1.  For each new packet received, the sequence
   number increases by 1, until it reaches the maximum value and then
   cycles back to 1.  For consecutive packets of a given flow, their
   sequence number must be continuous.

   The Originator field is set to the unique ID of the flow entrance
   node within the network.




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   For MPLS and SRv6 interworking case, the border node should copy
   Control Word information from the receiving header to the sending
   header, e.g, from MPLS CW to IPv6 CW.

4.  Operations of CW Options On Destination

   When the packet reaches the node identified in the Destination
   Address field of the outer IPv6 header, CW option is read and used
   for flow-specific treatment, such as packet replication and
   elimination.  The destination node may be each segment of Routing
   Header (RH) or final destination.  How to config flow-specific
   treatment on the destinaiton node and trigger this treatment is out
   the scope of this document.  Note that some processing may need flow
   states maintained on the node.

   The content of CW option must not be modified en route.  If the outer
   IPv6 header is not removed, the DOH with CW option is also not
   removed.  Some intentionally defined forwarding methods may
   frequently remove and add outer IPv6 header en route, in this case
   the DOH with CW option should also be removed and added.  If there
   are further outer IPv6 header encapsulated on the outer IPv6 header,
   e.g., an underlay traffic engineering path, the DOH with CW option is
   generally not necessary to copy to the further outer IPv6 header,
   since the flow-specific treatment is not usually configured on nodes
   along the underlay traffic engineering path to avoid too many flow
   states on intermediate nodes.

5.  IANA Considerations

   TBD

6.  Security Considerations

   TBD

7.  Acknowledgements

   TBD.

8.  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,
              <https://www.rfc-editor.org/info/rfc2119>.






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   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
              February 2006, <https://www.rfc-editor.org/info/rfc4385>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [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>.

   [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>.

   [RFC9343]  Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
              Pang, "IPv6 Application of the Alternate-Marking Method",
              RFC 9343, DOI 10.17487/RFC9343, December 2022,
              <https://www.rfc-editor.org/info/rfc9343>.

   [RFC9566]  Varga, B., Farkas, J., and A. Malis, "Deterministic
              Networking (DetNet) Packet Replication, Elimination, and
              Ordering Functions (PREOF) via MPLS over UDP/IP",
              RFC 9566, DOI 10.17487/RFC9566, April 2024,
              <https://www.rfc-editor.org/info/rfc9566>.

Author's Address

   Shaofu Peng
   ZTE Corporation
   China
   Email: peng.shaofu@zte.com.cn















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