Internet Engineering Task Force (IETF) B. Varga

Internet Engineering Task Force (IETF) B. Varga
Request for Comments: 9566 J. Farkas
Category: Informational Ericsson
ISSN: 2070-1721 A. Malis
Malis Consulting
April 2024

Deterministic Networking (DetNet) Packet Replication, Elimination, and
Ordering Functions (PREOF) via MPLS over UDP/IP

Abstract

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

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

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). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see 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
https://www.rfc-editor.org/info/rfc9566.

Copyright Notice

Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.

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Table of Contents

1. Introduction
2. Terminology
2.1. Terms Used in This Document
2.2. Abbreviations
3. Requirements for Adding PREOF to DetNet IP
4. Adding PREOF to DetNet IP
4.1. Solution Basics
4.2. Encapsulation
4.3. Packet Processing
4.4. Flow Aggregation
4.5. PREOF Processing
4.6. PREOF-Capable DetNet IP Domain
5. Control and Management Plane Parameters
6. Security Considerations
7. IANA Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Authors' Addresses

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 PRF and PEF is described in [IEEE8021CB], and the
related YANG data model is defined in [IEEE8021CBcv]. A possible
implementation of POF is described in [RFC9550]. Figure 1 shows a
DetNet flow on which PREOF are applied during forwarding from the
source to the destination.

+------------+
+---------------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 require sequencing information to be
included in the packets of a DetNet compound flow. This can be done
by adding a sequence number or timestamp 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 reusing 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 it is assumed that the reader is 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

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]), and

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

The described solution leverages 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 the 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 a UDP packet containing the sequence number used by
PREOF 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

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)
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
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 the Service-ID is a local ID on the receiver side that
identifies 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, and

* aggregation of DetNet flows as a new DetNet flow.

In the first method, 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 method, an additional hierarchy is created by adding
an additional Service-ID and d-CW tuple to the encapsulation. The
Aggregate-ID is a special case of a Service-ID, whose properties are
known only at the aggregation and deaggregation 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 the
case of aggregation.

+---------------------------------+
| |
| 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 aggregation method is configured in the aggregation/deaggregation
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 the received
packet. A unique Service-ID can be allocated and can be used to
identify a DetNet flow regardless of which input interface or UDP
tunnel receives the packet. 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
member flows, and each member flow requires its own Service-ID, UDP
header information, 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 by assigning a
Service-ID to the received DetNet flow and processing the information
in the UDP and IP headers. 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, and not only within
sub-networks, as is depicted in Figure 4 <https://www.rfc-
editor.org/rfc/rfc8939#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.

* 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 Differentiated Services Code Point (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

* Sequence number length

* Type of PREOF to be executed on the DetNet flow

* Service-ID(s) used by the member flows

* 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 Operations, Administration, and Maintenance (OAM)
techniques applicable [RFC9546]. Using the described encapsulation
only for a portion of a DetNet IP network that handles PREOF 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 has no IANA actions.

8. References

8.1. Normative References

[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>.

[RFC9546] Mirsky, G., Chen, M., and B. Varga, "Operations,
Administration, and Maintenance (OAM) for Deterministic
Networking (DetNet) with the MPLS Data Plane", RFC 9546,
DOI 10.17487/RFC9546, February 2024,
<https://www.rfc-editor.org/info/rfc9546>.

8.2. Informative References

[IEEE8021CB]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Frame Replication and Elimination for
Reliability", IEEE Std 802.1CB-2017,
DOI 10.1109/IEEESTD.2017.8091139, October 2017,
<https://doi.org/10.1109/IEEESTD.2017.8091139>.

[IEEE8021CBcv]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Frame Replication and Elimination for
Reliability - Amendment 1: Information Model, YANG Data
Model, and Management Information Base Module", Amendment
to IEEE Std 802.1CB-2017, IEEE Std 802.1CBcv-2021,
DOI 10.1109/IEEESTD.2022.9715061, February 2022,
<https://doi.org/10.1109/IEEESTD.2022.9715061>.

[RFC9550] Varga, B., Ed., Farkas, J., Kehrer, S., and T. Heer,
"Deterministic Networking (DetNet): Packet Ordering
Function", RFC 9550, DOI 10.17487/RFC9550, March 2024,
<https://www.rfc-editor.org/info/rfc9550>.

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.

Authors' Addresses

Balazs Varga
Ericsson
Budapest
Magyar Tudosok krt. 11.
1117
Hungary
Email: [email protected]

Janos Farkas
Ericsson
Budapest
Magyar Tudosok krt. 11.
1117
Hungary
Email: [email protected]

Andrew G. Malis
Malis Consulting
Email: [email protected]