Control Word Option
draft-peng-6man-cw-option-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Shaofu Peng | ||
| Last updated | 2026-01-20 | ||
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draft-peng-6man-cw-option-01
Network Shaofu. Peng
Internet-Draft ZTE Corporation
Intended status: Standards Track 20 January 2026
Expires: 24 July 2026
Control Word Option
draft-peng-6man-cw-option-01
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.
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 24 July 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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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 . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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 mainly used for load distribution, instead of a
discriminator for the original customer flows. Multiple customer
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flows may be encapsulated in outer IPv6 packets that use the same
Flow Label, regardless of the Flow Label of the encapsulated packets.
[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 (CW) 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. The CW option is not
intended to be used across the global Internet, but within a limited
domain [RFC8799].
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 elimination and
reordering. 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
This document updates the "Destination Options and Hop-by-Hop
Options" under the "Internet Protocol Version 6 (IPv6) Parameters"
registry:
+---------+-----+-----+------+-----------------------+-------------+
|Hex Value| act | chg | rest | Description | Reference |
+---------+-----+-----+------+-----------------------+-------------+
| TBD | 00 | 1 | 00000| Control Word Option |This document|
+---------+-----+-----+------+-----------------------+-------------+
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6. Security Considerations
Malicious tampering with any field in the CW option can result in
corresponding processing exceptions. For example, tampering with the
Flow Identity may result in packets being incorrectly identified as
unrelated flows, and tampering with the Sequence Number may result in
packets being mistakenly discarded as redundant packets. Therefore,
the CW option must only be applied in a limited domain, where all
nodes in the domain are trusted. Other common security
considerations are described in [RFC8200], [RFC9099].
7. Acknowledgements
The authors would like to thank Brian Carpenter for his review and
valuable comments.
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>.
[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
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[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>.
[RFC9099] Vyncke, É., Chittimaneni, K., Kaeo, M., and E. Rey,
"Operational Security Considerations for IPv6 Networks",
RFC 9099, DOI 10.17487/RFC9099, August 2021,
<https://www.rfc-editor.org/info/rfc9099>.
[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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