DetNet B. Varga
Internet-Draft J. Farkas
Intended status: Informational Ericsson
Expires: December 11, 2021 A. Malis
Malis Consulting
June 9, 2021
Deterministic Networking (DetNet): PREOF for DetNet IP
draft-varga-detnet-ip-preof-00
Abstract
This document describes how DetNet IP data plane can support the
Packet Replication, Elimination, and Ordering Functions (PREOF) based
on [RFC9025].
Status of This Memo
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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
2.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . . . . . . . . 6
4.4. Flow Aggregation . . . . . . . . . . . . . . . . . . . . 6
4.5. PREOF Procedures . . . . . . . . . . . . . . . . . . . . 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. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The DetNet Working Group has defined packet replication (PRF), packet
elimination (PEF) and packet ordering (POF) functions 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 POF function is described in
[I-D.varga-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 may 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 [RFC8939] 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 header. This document describes
a DetNet IP encapsulation that includes sequencing information based
on the DetNet MPLS over UDP/IP data plane [RFC9025], i.e., leveraging
the MPLS-over-UDP technology.
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.
POF Packet Ordering Function.
PREOF Packet Replication, Elimination and Ordering Functions.
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PRF Packet Replication Function.
2.3. 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.
3. Requirements for adding PREOF to DetNet IP
The requirements for adding PREOF to DetNet IP are:
o to reuse existing DetNet data plane solutions (e.g., [RFC8964],
[RFC9025]).
o to allow with minimal implementation effort the DetNet service
sub-layer for IP packet switched networks.
The described solution practically gains from MPLS header fields
without adding MPLS protocol stack complexity to the nodal
requirements.
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. 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.
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DetNet IP
.
.
+------------+
| Service | d-CW, Service-ID (S-label)
+------------+
| Forwarding | UDP/IP Header
+------------+
Figure 2: PREOF capable DetNet IP data plane
4.2. Encapsulation
The PREOF capable DetNet IP encapsulation builds on encapsulating
DetNet 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
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4.3. Packet Processing
IP ingress and egress nodes of the PREOF capable DetNet IP domain
MUST add and remove a DetNet service-specific d-CW and Service-ID
(i.e., S-Label). Relay nodes MAY 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 MUST be
provisioned per DetNet service via configuration, i.e., via the
Controller Plane described in [RFC8938]. In some PREOF topologies,
the node performing replication sends the packets to multiple nodes
performing PEF or POF and the replication node may need to use
different Service-ID values for the different member flows for the
same DetNet service.
Note, that Service-IDs provide identification at the downstream
DetNet service sub-layer receiver, not the sender.
4.4. Flow Aggregation
Two methods can be used for flow aggregation:
o aggregation using same UDP tunnel,
o aggregating DetNet flows as a new DetNet flow.
In the first case, the different DetNet PWs use the same UDP tunnel,
so they are treated as a single (aggregated) flow on all transit
nodes.
For the second option, an additional Service-ID and d-CW tuple is
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 an 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
4.5. PREOF Procedures
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 may 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.
To support outgoing PREOF capable DetNet IP encapsulation, an
implementation MUST support 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
the of their own Service-ID, UDP and IP header information. The
headers for each outgoing packet MUST be formatted according to the
configuration information, and the UDP Source Port value MUST be set
to uniquely identify the DetNet flow. The packet MUST then be
handled as a PREOF capable DetNet IP packet.
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To support the receive processing, an implementation MUST also
support the provisioning of received Service-ID, UDP and IP header
information. The provisioned information MUST be used to identify
incoming app-flows based on the combination of Service-ID and/or
incoming encapsulation header information.
The challenge for POF initialization is that, for example, after a
reset, it is not known whether the first received packet is in-order
or out-of-order. The original initialization (see
[I-D.varga-detnet-pof]) considers the first packet as in-order, so
out-of-order packet(s) during "POFMaxTime"/"POFMaxTime_path_i" time -
after the first packet was received - may not be corrected. The
motivation behind such an initialization is POF implementation
simplicity.
4.6. PREOF capable DetNet IP domain
Figure 5 shows using PREOF in a PREOF capable DetNet IP network.
<---------- 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:
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o 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.
o IPv4 or IPv6 source address field.
o IPv4 or IPv6 source address prefix length, where a zero (0) value
effectively means that the address field is ignored.
o IPv4 or IPv6 destination address field.
o IPv4 or IPv6 destination address prefix length, where a zero (0)
effectively means that the address field is ignored.
o IPv4 protocol field set to "UDP".
o IPv6 next header field set to "UDP".
o 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.
o UDP Source Port. Support for both exact and wildcard matching is
required. Port ranges can optionally be used.
o UDP Destination Port. Support for both exact and wildcard
matching is required. Port ranges can optionally be used.
o For end systems, an optional maximum IP packet size that should be
used for that outgoing DetNet IP flow.
This information MUST be provisioned per DetNet flow via
configuration, e.g., via the controller plane.
An implementation MUST support ordering of the set of information
used to identify an individual DetNet flow. This 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:
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o App-flow identification information.
o Sequence number length.
o PREOF + related Service-ID(s).
o Associated forwarding sub-layer information.
o Service aggregation information.
The minimum set of information for the configuration of the DetNet
forwarding sub-layer is summarized as follows:
o UDP tunnel specific information.
o Traffic parameters.
6. Security Considerations
There are no new DetNet related security considerations introduced by
this solution.
7. IANA Considerations
This document makes no IANA requests.
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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
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[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>.
[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>.
8.2. Informative References
[I-D.varga-detnet-pof]
Varga, B., Farkas, J., Kehrer, S., and T. Heer,
"Deterministic Networking (DetNet): Packet Ordering
Function", draft-varga-detnet-pof-00 (work in progress),
April 2021.
[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
Magyar Tudosok krt. 11.
Budapest 1117
Hungary
Email: balazs.a.varga@ericsson.com
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Janos Farkas
Ericsson
Magyar Tudosok krt. 11.
Budapest 1117
Hungary
Email: janos.farkas@ericsson.com
Andrew G. Malis
Malis Consulting
Email: agmalis@gmail.com
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