MPLS Working Group T. Saad
Internet-Draft Juniper Networks
Intended status: Informational K. Makhijani
Expires: 11 July 2022 H. Song
Futurewei Technologies
7 January 2022
Usecases for MPLS Indicators and Ancillary Data
draft-saad-mpls-miad-usecases-00
Abstract
This document presents a number of use cases that have a common need
for encoding MPLS function indicators and ancillary data inside MPLS
packets. The use cases described are not an exhaustive set, but
rather the ones that are actively discussed at the MPLS Working
Group.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 11 July 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Acronyms and Abbreviations . . . . . . . . . . . . . . . 3
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. In-situ OAM . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Network Slicing . . . . . . . . . . . . . . . . . . . . . 4
2.2.1. Global Identifier as Slice Selector . . . . . . . . . 5
2.2.2. Forwarding Label as a Slice Selector . . . . . . . . 6
2.3. Time Sensitive Networking . . . . . . . . . . . . . . . . 6
2.3.1. Stack-based Methods for Latency Control . . . . . . . 6
2.3.2. Stack Entry Format . . . . . . . . . . . . . . . . . 7
2.4. NSH Based Service Function Chaining . . . . . . . . . . . 7
2.5. Network Programming . . . . . . . . . . . . . . . . . . . 7
2.6. Application Aware Networking (APN) . . . . . . . . . . . 8
3. Co-existence of Usecases . . . . . . . . . . . . . . . . . . 8
3.1. IOAM with Network Slicing . . . . . . . . . . . . . . . . 8
3.2. IOAM with Time Sensitive Networking . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 9
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document describes important cases that require carrying
additional ancillary data within the MPLS packets, as well as the
means to indicate ancillary data is present.
These use cases have been identified by the MPLS working group design
team working on defining MPLS function indicators and ancillary data
for the MPLS data plane. The use cases described in this document
will be used to assist in identifying requirements and issues to be
considered for future resolution by the working group.
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* ID: draft-gandhi-mpls-ioam describes applicability of IOAM to MPLS
dataplane.
* RFC 8986 describes the network programming usecase for SRv6
dataplane.
* RFC 8595 describes solution for MPLS-based forwarding for Service
Function Chaining
1.1. Terminology
The following terminology is used in the document:
IETF Network Slice:
a well-defined composite of a set of endpoints, the connectivity
requirements between subsets of these endpoints, and associated
requirements; the term 'network slice' in this document refers to
'IETF network slice' as defined in
[I-D.ietf-teas-ietf-network-slices].
IETF Network Slice Controller (NSC):
controller that is used to realize an IETF network slice
[I-D.ietf-teas-ietf-network-slices].
Network Resource Partition:
the collection of resources that are used to support a slice
aggregate.
Time Sensitive Networking:
Networks that transport time sensitive traffic.
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.
1.2. Acronyms and Abbreviations
MIAD: MPLS Label Stack Indicators for Ancillary Data
ISD: In-stack data
PSD: Post-stack data
MPLS: Multiprotocol Label Switching
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2. Use Cases
2.1. In-situ OAM
In-situ Operations, Administration, and Maintenance (IOAM) records
operational and telemetry information within the packet while the
packet traverses a particular path in a network domain.
The term "in-situ" refers to the fact that the IOAM data fields are
added to the data packets rather than being sent within the probe
packets specifically dedicated to OAM or Performance Measurement
(PM).
IOAM can run in two modes End-to-End (E2E) and Hop-by-Hop (HbH). In
E2E mode, only the encapsulating and decapsulating nodes will process
IOAM data fields. In HbH mode, the encapsulating and decapsulating
nodes as well as intermediate nodes process IOAM data fields.
The IOAM data fields are defined in [I-D.ietf-ippm-ioam-data], and
can be used for various use-cases of OAM and PM.
[I-D.gandhi-mpls-ioam-sr] defines how IOAM data fields are
transported using the MPLS data plane encapsulations, including
Segment Routing (SR) with MPLS data plane (SR-MPLS).
IOAM data are added after the bottom of the label stack. The IOAM
data fields can be of fixed or incremental size as defined in
[I-D.ietf-ippm-ioam-data]. [I-D.gandhi-mpls-ioam] describes
applicability of IOAM to MPLS dataplane. The encapsulating MPLS node
needs to know if the decapsulating MPLS node can process the IOAM
data before adding it in the packet.
2.2. Network Slicing
[I-D.ietf-teas-ietf-network-slices] specifies the definition of a
network slice for use within the IETF and discusses the general
framework for requesting and operating IETF Network Slices, their
characteristics, and the necessary system components and interfaces.
Multiple network slices can be realized on top of a single shared
network.
In order to overcome scale challenges, IETF Network Slices may be
aggregated into groups according to similar characteristics. The
slice aggregate [I-D.bestbar-teas-ns-packet] is a construct that
comprises of the traffic flows of one or more IETF Network Slices of
similar characteristics.
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A router that requires forwarding of a packet that belongs to a slice
aggregate may have to decide on the forwarding action to take based
on selected next-hop(s), and the forwarding treatment (e.g.,
scheduling and drop policy) to enforce based on the associated per-
hop behavior.
The routers in the network that forward traffic over links that are
shared by multiple slice aggregates need to identify the slice
aggregate packets in order to enforce the associated forwarding
action and treatment.
An IETF network slice need MAY support the following key features:
1. A Slice Selector
2. A Network Resource Partition associated with a slice aggregate.
3. A Path selection criteria
4. Verification that per slice SLOs are being met. This may be done
by active measurements (inferred) or by using IOAM.
5. Additionally, there is an on-going discussion on using Service
Functions (SFs) with network slices. This may require insertion
of an NSH.
6. For multi-domain scenarios, a packet that traverses multiple
domains may encode different identifiers within each domain.
2.2.1. Global Identifier as Slice Selector
A Global Identifier as a Slice Selector (GISS) can be encoded in the
MPLS packet as defined in [I-D.kompella-mpls-mspl4fa],
[I-D.li-mpls-enhanced-vpn-vtn-id], and
[I-D.decraene-mpls-slid-encoded-entropy-label-id]. The Global
Identifier Slice Selector can be used to associate the packets to the
slice aggregate, independent of the MPLS forwarding label that is
bound to the destination. LSRs use the MPLS forwarding label to
determine the forwarding next-hop(s), and use the Global Identifier
Slice Selector field in the packet to infer the specific forwarding
treatment that needs to be applied on the packet.
The GISS can be encoded within an MPLS label that is carried in the
packet's MPLS label stack. All packets that belong to the same slice
aggregate MAY carry the same GISS in the MPLS label stack. It is
also possible to have multiple GISS's map to the same slice
aggregate. The GISS can be encoded in an MPLS label and may appear
in several positions in the MPLS label stack.
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2.2.2. Forwarding Label as a Slice Selector
[RFC3031] states in Section 2.1 that: 'Some routers analyze a
packet's network layer header not merely to choose the packet's next
hop, but also to determine a packet's "precedence" or "class of
service"'.
It is possible by assigning a unique MPLS forwarding label to each
slice aggregate (FEC) to distinguish the packets forwarded to the
same destination but that belong to different slice aggregates. In
this case, LSRs can use the top forwarding label to infer both the
forwarding action and the forwarding treatment to be invoked on the
packets. A similar approach is described in
[I-D.ietf-spring-resource-aware-segments] and
[I-D.bestbar-teas-ns-packet].
2.3. Time Sensitive Networking
The routers in a network can perform two distinct functions on
incoming packets, namely forwarding (where the packet should be sent)
and scheduling (when the packet should be sent). Time Sensitive
Networking (TSN) and Deterministic Networking provide several
mechanisms for scheduling under the assumption that routers are time
synchronized. The most effective mechanisms for delay minimization
involve per-flow resource allocation.
Segment Routing (SR) is a forwarding paradigm that allows encoding
forwarding instructions in the packet in a stack data structure,
rather than being programmed into the routers. The SR instructions
are contained within a packet in the form of a first-in first-out
stack dictating the forwarding decisions of successive routers.
Segment routing may be used to choose a path sufficiently short to be
capable of providing sufficiently low end- to-end latency but does
not influence the queueing of individual packets in each router along
that pat
TSN is required for networks transporting time sensitive traffic,
that is, packets that are required to be delivered to their final
destination by a given time.
2.3.1. Stack-based Methods for Latency Control
One efficient data structure for inserting local deadlines into the
headers is a "stack", similar to that used in Segment Routing to
carry forwarding instructions. The number of deadline values in the
stack equals the number of routers the packet needs to traverse in
the network, and each deadline value corresponds to a specific
router. The Top-of-Stack (ToS) corresponds to the first router's
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deadline while the Bottom-of-Stack (BoS) refers to the last's. All
local deadlines in the stack are later or equal to the current time
(upon which all routers agree), and times closer to the ToS are
always earlier or equal to times closer to the BoS.
The ingress router inserts the deadline stack into the packet
headers; no other router needs to be aware of the requirements of the
time sensitive flows. Hence admitting a new flow only requires
updating the information base of the ingress router.
MPLS LSRs that expose the Top of Stack (ToS) label can also inspect
the associated "deadline" carried in the packet (either in MPLS stack
or after BoS).
2.3.2. Stack Entry Format
A number of different time formats commonly used in networking
applications and can be used to encode the local deadlines.
For the forwarding sub-entry we could adopt like SR-MPLS standard
32-bit MPLS labels (which contain a 20-bit label and BoS bit), and
thus SR-TSN stack entries could be 64-bits in size comprising a
32-bit MPLS label and the aforementioned nonstandard 32-bit
timestamp.
Alternatively, an SR-TSN stack entry could be 96 bits in length
comprising a 32-bit MPLS label and either of the standardized 64-bit
timestamps.
2.4. NSH Based Service Function Chaining
The Network Service Header (NSH) can be embedded in an Extended
Header (EH) to support the Path ID and any metadata that needs to be
carried and exchanged between Service Function Forwarders (SFFs).
A reference to the NSH SFC use case is defined in [RFC8596].
2.5. Network Programming
In SR, an ingress node steers a packet through an ordered list of
instructions, called "segments". Each one of these instructions
represents a function to be called at a specific location in the
network. A function is locally defined on the node where it is
executed and may range from simply moving forward in the segment list
to any complex user-defined behavior.
Network Programming combines Segment Routing (SR) functions to
achieve a networking objective that goes beyond mere packet routing.
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It may be desirable to encode a pointers to function and its
function-arguments within an MPLS packet transport header. For
example, in MPLS we can encode the FUNC::ARGs within the label stack
or after the bottom of stack to support the equivalent of FUNC::ARG
in SRv6 as described in [RFC8986].
2.6. Application Aware Networking (APN)
Application-aware Networking (APN) allows application-aware
information (i.e., APN attribute) including APN identification (ID)
and/or APN parameters (e.g. network performance requirements) to be
encapsulated at network edge devices and carried in packets
traversing an APN domain in order to facilitate service provisioning,
perform fine-granularity traffic steering and network resource
adjustment. To support APN in MPLS networks, mechanisms are needed
to hold the APN attribute.
3. Co-existence of Usecases
Two or more of the aforementioned use cases MAY co-exist in the same
packet. Some examples of such usecases are described below.
3.1. IOAM with Network Slicing
IOAM may provide key functions with network slicing to help ensure
that critical network slice SLOs are being met by the network
provider.
In such a case, IOAM is able collect key performance measurement
parameters of network slice traffic flows as it traverses the
transport network.
This may require, in addition to carrying a specific network slice
selector (e.g., GISS), the MPLS network slice packets may have to
also carry IOAM ancillary data.
Note that the IOAM ancillary data may have to be modified, and
updated on some/all LSRs traversed by the network slice MPLS packets.
3.2. IOAM with Time Sensitive Networking
IOAM operation may also be desirable on MPLS packets that carry time-
sensitive related data. Similarly, this may require the presence of
multiple ancillary data (whether In-stack or Post-stack ancillary
data) to be present in the same MPLS packet.
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4. IANA Considerations
This document has no IANA actions.
5. Security Considerations
This document introduces no new security considerations.
6. Acknowledgement
The authors gratefully acknowledge the input of the members of the
MPLS Open Design Team.
7. Contributors
The following individuals contributed to this document:
Kiran Makhijani
Futurewei Technologies
Email: kiranm@futurewei.com
Haoyu Song
Futurewei Technologies
Email: haoyu.song@futurewei.com
Loa Andersson
Bronze Dragon Consulting
Email: loa@pi.nu
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>.
8.2. Informative References
[I-D.bestbar-teas-ns-packet]
Saad, T., Beeram, V. P., Wen, B., Ceccarelli, D., Halpern,
J., Peng, S., Chen, R., Liu, X., Contreras, L. M., Rokui,
R., and L. Jalil, "Realizing Network Slices in IP/MPLS
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Networks", Work in Progress, Internet-Draft, draft-
bestbar-teas-ns-packet-06, 22 December 2021,
<https://www.ietf.org/archive/id/draft-bestbar-teas-ns-
packet-06.txt>.
[I-D.decraene-mpls-slid-encoded-entropy-label-id]
Decraene, B., Filsfils, C., Henderickx, W., Saad, T.,
Beeram, V. P., and L. Jalil, "Using Entropy Label for
Network Slice Identification in MPLS networks.", Work in
Progress, Internet-Draft, draft-decraene-mpls-slid-
encoded-entropy-label-id-02, 6 August 2021,
<https://www.ietf.org/archive/id/draft-decraene-mpls-slid-
encoded-entropy-label-id-02.txt>.
[I-D.gandhi-mpls-ioam]
Gandhi, R., Ali, Z., Brockners, F., Wen, B., Decraene, B.,
and V. Kozak, "MPLS Data Plane Encapsulation for In-situ
OAM Data", Work in Progress, Internet-Draft, draft-gandhi-
mpls-ioam-01, 9 September 2021,
<https://www.ietf.org/archive/id/draft-gandhi-mpls-ioam-
01.txt>.
[I-D.gandhi-mpls-ioam-sr]
Gandhi, R., Ali, Z., Filsfils, C., Brockners, F., Wen, B.,
and V. Kozak, "MPLS Data Plane Encapsulation for In-situ
OAM Data", Work in Progress, Internet-Draft, draft-gandhi-
mpls-ioam-sr-06, 18 February 2021,
<https://www.ietf.org/archive/id/draft-gandhi-mpls-ioam-
sr-06.txt>.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", Work in Progress, Internet-Draft, draft-
ietf-ippm-ioam-data-17, 13 December 2021,
<https://www.ietf.org/archive/id/draft-ietf-ippm-ioam-
data-17.txt>.
[I-D.ietf-spring-resource-aware-segments]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Introducing Resource Awareness to SR
Segments", Work in Progress, Internet-Draft, draft-ietf-
spring-resource-aware-segments-03, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-spring-
resource-aware-segments-03.txt>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L. M., and J. Tantsura,
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"Framework for IETF Network Slices", Work in Progress,
Internet-Draft, draft-ietf-teas-ietf-network-slices-05, 25
October 2021, <https://www.ietf.org/archive/id/draft-ietf-
teas-ietf-network-slices-05.txt>.
[I-D.kompella-mpls-mspl4fa]
Kompella, K., Beeram, V. P., Saad, T., and I. Meilik,
"Multi-purpose Special Purpose Label for Forwarding
Actions", Work in Progress, Internet-Draft, draft-
kompella-mpls-mspl4fa-01, 12 July 2021,
<https://www.ietf.org/archive/id/draft-kompella-mpls-
mspl4fa-01.txt>.
[I-D.li-mpls-enhanced-vpn-vtn-id]
Li, Z. and J. Dong, "Carrying Virtual Transport Network
Identifier in MPLS Packet", Work in Progress, Internet-
Draft, draft-li-mpls-enhanced-vpn-vtn-id-01, 14 April
2021, <https://www.ietf.org/archive/id/draft-li-mpls-
enhanced-vpn-vtn-id-01.txt>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC8596] Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
"MPLS Transport Encapsulation for the Service Function
Chaining (SFC) Network Service Header (NSH)", RFC 8596,
DOI 10.17487/RFC8596, June 2019,
<https://www.rfc-editor.org/info/rfc8596>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
Authors' Addresses
Tarek Saad
Juniper Networks
Email: tsaad@juniper.net
Kiran Makhijani
Futurewei Technologies
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Email: kiranm@futurewei.com
Haoyu Song
Futurewei Technologies
Email: haoyu.song@futurewei.com
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