Internet DRAFT - draft-ietf-mpls-mna-usecases
draft-ietf-mpls-mna-usecases
MPLS Working Group T. Saad
Internet-Draft Cisco Systems, Inc.
Intended status: Informational K. Makhijani
Expires: 13 August 2024 H. Song
Futurewei Technologies
G. Mirsky
Ericsson
10 February 2024
Use Cases for MPLS Network Action Indicators and MPLS Ancillary Data
draft-ietf-mpls-mna-usecases-04
Abstract
This document presents a number of use cases that have a common need
for encoding network action indicators and associated ancillary data
inside MPLS packets. There has been significant recent interest in
extending the MPLS data plane to carry such indicators and ancillary
data to address a number of use cases that are described in this
document.
The use cases described in this document are not an exhaustive set,
but rather the ones that are actively discussed by members of the
IETF MPLS, PALS, and DetNet.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 13 August 2024.
Copyright Notice
Copyright (c) 2024 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Conventions used in this document . . . . . . . . . . . . 3
1.2.1. Keywords . . . . . . . . . . . . . . . . . . . . . . 3
1.2.2. Acronyms and Abbreviations . . . . . . . . . . . . . 3
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. No Further Fastreroute . . . . . . . . . . . . . . . . . 4
2.2. In-situ OAM . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Network Slicing . . . . . . . . . . . . . . . . . . . . . 5
2.4. NSH-based Service Function Chaining . . . . . . . . . . . 6
2.5. Network Programming . . . . . . . . . . . . . . . . . . . 6
3. Existing MPLS Use cases . . . . . . . . . . . . . . . . . . . 7
4. Co-existence of the MNA Usecases . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Use Cases for Continued Discussion . . . . . . . . . 11
A.1. Generic Delivery Functions . . . . . . . . . . . . . . . 11
A.2. Delay Budgets for Time-Bound Applications . . . . . . . . 11
A.3. Stack-Based Methods for Latency Control . . . . . . . . . 12
Contributors' Addresses . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This document describes cases that introduce functions that are based
on special processing by forwarding hardware. Previously, that
required the allocation of a new special-purpose label or extended
special-purpose label. To conserve that limited resource, an MPLS
Network Action (MNA) approach was introduced to extend the MPLS
architecture. MNA is expected to enable functions that may require
carrying additional ancillary data within the MPLS packets, as well
as means to indicate the ancillary data is present and a specific
action needs to be performed on the packet. The MPLS Ancillary Data
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(AD) can be classified as:
* implicit or "no-data" associated with a Network Action Indicator
(NAI),
* residing within the MPLS label stack and referred to as In Stack
Data (ISD), and
* residing after the Bottom of the MPLS label Stack (BoS) and
referred to as Post Stack Data (PSD).
1.1. Terminology
The following terminology is used in the document:
RFC XXXX 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
'RFC XXXX network slice' as defined in
[I-D.ietf-teas-ietf-network-slices].
1.2. Conventions used in this document
1.2.1. Keywords
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.
1.2.2. Acronyms and Abbreviations
ISD: In-stack data
PSD: Post-stack data
MNA: MPLS Network Action
NAI: Network Action Indicator
AD: Ancillary Data
DEX: Direct Export
GDF: Generic Delivery Function
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E2E: Edge-to-Edge
HbH: Hop-by-Hop
PW: Pseudowire
BoS: Bottom of Stack
ToS: Top of Stack
NSH: Network Service Header
FRR: Fast Reroute
IOAM: In-situ Operations, Administration, and Mantenance
FAS: Flow Aggregate Selector
G-ACh: Generic Associated Channel
2. Use Cases
2.1. No Further Fastreroute
MPLS Fast Reroute (FRR) [RFC4090], [RFC5286] and [RFC7490] is a
useful and widely deployed tool for minimizing packet loss in the
case of a link or node failure.
Several cases exist where, once an FRR has taken place in an MPLS
network and resulted in rerouting a packet away from the failure, a
second FRR impacts the same packet on another node, and may result in
traffic disruption.
In such a case, the packet impacted by multiple FRR events may
continue to loop between the LSRs that activated FRR until the
packet's TTL expires. This can lead to link congestion and further
packet loss.
2.2. In-situ OAM
In-situ Operations, Administration, and Maintenance (IOAM), defined
in [RFC9197] and [RFC9326], might be used to collect operational and
telemetry information while a packet traverses a particular path in a
network domain.
IOAM can run in two modes: Edge-to-Edge (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
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decapsulating nodes, as well as intermediate IOAM-capable nodes,
process IOAM data fields. The IOAM data fields, defined in
[RFC9197], can be used to derive the operational state of the network
experienced by the packet with the IOAM Header that traversed the
path through the IOAM domain.
Several IOAM Trace Options have been defined:
* Pre-allocated and Incremental
* Edge-to-Edge
* Proof-of-Transit
* Direct Export (DEX)
In all IOAM Trace Options except for the Direct Export (DEX), the
collected information is transported in the trigger IOAM packet. In
the IOAM DEX Option [RFC9326], the operational state and telemetry
information are collected according to a specified profile and
exported in a manner and format defined by a local policy. In IOAM
DEX, the user data packet is only used to trigger the IOAM data to be
directly exported or locally aggregated without being carried in the
IOAM trigger packets.
2.3. Network Slicing
An RFC XXXX Network Slice service
([I-D.ietf-teas-ietf-network-slices]) provides connectivity coupled
with a set of network resource commitments and is expressed in terms
of one or more connectivity constructs.
[I-D.ietf-teas-ietf-network-slices] also defines a Network Resource
Partition (NRP) Policy as a policy construct that enables the
instantiation of mechanisms to support one or more network slice
services. The packets associated with an NRP may carry a marking in
their network layer header to identify this association, which is
referred to as an NRP Selector. The NRP Selector is used to map a
packet to the associated set of network resources and provide the
corresponding forwarding treatment onto the packet.
A router that requires the forwarding of a packet that belongs to an
NRP 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.
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In this case, the routers that forward traffic over resources that
are shared by multiple NRPs need to identify the slice aggregate
packets in order to enforce their respective forwarding action and
treatment.
A dedicated identifier that is independent of forwarding can be
carried and used in the packet as an NRP Selector. In MPLS, the NRP
Selector can be carried in a packet in the MPLS header.
2.4. NSH-based Service Function Chaining
[RFC8595] describes how Service Function Chaining can be realized in
an MPLS network by emulating the Network Service Header (NSH) using
only MPLS label stack elements.
The approach in [RFC8595] introduces some limitations that are
discussed in [I-D.lm-mpls-sfc-path-verification]. This approach,
however, can benefit from the framework introduced with MNA in
[I-D.ietf-mpls-mna-fwk].
For example, it may be possible to extend NSH emulation using MPLS
labels [RFC8595] to support the functionality of NSH Context Headers,
whether fixed or variable-length. One of the use cases could support
Flow ID [RFC9263] that may be used for load-balancing among Service
Function Forwarders and/or the Service Function within the same
Service Function Path.
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.
It may be desirable to encode a pointer to a function and its
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 (BoS) to support the equivalent of FUNC::ARG in
SRv6 as described in [RFC8986].
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3. Existing MPLS Use cases
There are several services that can be transported over MPLS networks
today. These include providing Layer-3 (L3) connectivity (e.g., for
unicast and multicast L3 services), and Layer-2 (L2) connectivity
(e.g., for unicast Pseudowires (PWs), multicast E-Tree, and broadcast
E-LAN L2 services). In those cases, the user service traffic is
encapsulated as the payload in MPLS packets.
For L2 service traffic, it is possible to use A Control Word (CW)
[RFC4385] and [RFC5085] immediately after the MPLS header to
disambiguate the type of MPLS payload, prevent possible packet
misordering, and allow for fragmentation. In this case, the first
nibble the data that immediately follows after the MPLS BoS is set to
0000b to identify the presence of PW CW.
In addition to providing connectivity to user traffic, MPLS may also
transport OAM data (e.g., over MPLS Generic Associated Channels
(G-AChs) [RFC5586]). In this case, the first nibble of the data that
immediately follows after the MPLS BoS is set to 0001b. It indicates
the presence of a control channel associated witha PW, LSP, or
Section.
Bit Index Explicit Replication (BIER) [RFC8296] traffic can also be
encapsulated over MPLS. In this case, BIER has defined 0101b as the
value for the first nibble in the data that immediately appears after
the bottom of the label stack for any BIER encapsulated packet over
MPLS.
For pseudowires, the G-ACh uses the first four bits of the PW control
word to provide the initial discrimination between data packets and
packets belonging to the associated channel, as described in
[RFC4385].
It is expected that new use cases described in this document will
allow for the co-existance and backward compatibility with all such
existing MPLS services.
4. Co-existence of the MNA Usecases
Two or more of the aforementioned use cases MAY co-exist in the same
packet. This may require the presence of multiple ancilary data
(whether In-stack or Post-stack ancillary data) to be present in the
same MPLS packet.
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For example, IOAM may provide key functions along with network
slicing to help ensure that critical network slice SLOs are being met
by the network provider. In this case, IOAM is able to collect key
performance measurement parameters of network slice traffic flow as
it traverses the transport network.
5. IANA Considerations
This document has no IANA actions.
6. Security Considerations
This document introduces no new security considerations.
7. Acknowledgement
The authors gratefully acknowledge the input of the members of the
MPLS Open Design Team.
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.ietf-mpls-mna-fwk]
Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions Framework", Work in Progress, Internet-
Draft, draft-ietf-mpls-mna-fwk-06, 24 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-fwk-06>.
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[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "A Framework for
Network Slices in Networks Built from IETF Technologies",
Work in Progress, Internet-Draft, draft-ietf-teas-ietf-
network-slices-25, 14 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slices-25>.
[I-D.lm-mpls-sfc-path-verification]
Liu, Y. and G. Mirsky, "MPLS-based Service Function
Path(SFP) Consistency Verification", Work in Progress,
Internet-Draft, draft-lm-mpls-sfc-path-verification-03, 11
June 2022, <https://datatracker.ietf.org/doc/html/draft-
lm-mpls-sfc-path-verification-03>.
[I-D.stein-srtsn]
Stein, Y. J., "Segment Routed Time Sensitive Networking",
Work in Progress, Internet-Draft, draft-stein-srtsn-01, 29
August 2021, <https://datatracker.ietf.org/doc/html/draft-
stein-srtsn-01>.
[I-D.zzhang-intarea-generic-delivery-functions]
Zhang, Z. J., Bonica, R., Kompella, K., and G. Mirsky,
"Generic Delivery Functions", Work in Progress, Internet-
Draft, draft-zzhang-intarea-generic-delivery-functions-03,
11 July 2022, <https://datatracker.ietf.org/doc/html/
draft-zzhang-intarea-generic-delivery-functions-03>.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.
[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>.
[RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
Circuit Connectivity Verification (VCCV): A Control
Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
December 2007, <https://www.rfc-editor.org/info/rfc5085>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>.
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[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015,
<https://www.rfc-editor.org/info/rfc7490>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8595] Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
Forwarding Plane for Service Function Chaining", RFC 8595,
DOI 10.17487/RFC8595, June 2019,
<https://www.rfc-editor.org/info/rfc8595>.
[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>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/info/rfc9197>.
[RFC9263] Wei, Y., Ed., Elzur, U., Majee, S., Pignataro, C., and D.
Eastlake 3rd, "Network Service Header (NSH) Metadata Type
2 Variable-Length Context Headers", RFC 9263,
DOI 10.17487/RFC9263, August 2022,
<https://www.rfc-editor.org/info/rfc9263>.
[RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
Mizrahi, "In Situ Operations, Administration, and
Maintenance (IOAM) Direct Exporting", RFC 9326,
DOI 10.17487/RFC9326, November 2022,
<https://www.rfc-editor.org/info/rfc9326>.
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Appendix A. Use Cases for Continued Discussion
A number of use cases for which MNA can provide a viable solution
have been brought up. The discussion of these aspirational cases is
ongoing.
A.1. Generic Delivery Functions
The Generic Delivery Functions (GDFs), defined in
[I-D.zzhang-intarea-generic-delivery-functions], provide a new
mechanism to support functions analogous to those supported through
the IPv6 Extension Headers mechanism. For example, GDF can support
fragmentation/reassembly functionality in the MPLS network by using
the Generic Fragmentation Header. MNA can support GDF by placing a
GDF header in an MPLS packet within the Post-Stack Data block
[I-D.ietf-mpls-mna-fwk]. Multiple GDF headers can also be present in
the same MPLS packet organized as a list of headers.
A.2. Delay Budgets for Time-Bound Applications
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). IEEE-802.1 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 a bounded end-to-end latency but does not
influence the queueing of individual packets in each router along
that path.
When carried over the MPLS data plane, a solution is required to
enable the delivery of such packets that can be delivered to their
final destination within a given time budget. One approach to
address this usecase in SR-MPLS was described in [I-D.stein-srtsn].
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A.3. 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
deadline, while the BoS refers to the last. 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-bound flows. Hence, admitting a new flow only requires updating
the information base of the ingress router.
MPLS LSRs that expose the ToS label can also inspect the associated
"deadline" carried in the packet (either in the MPLS stack as ISD or
after BoS as PSD).
Contributors' Addresses
Loa Anderssen
Bronze Dragon Consulting
Email: loa@pi.nu
Authors' Addresses
Tarek Saad
Cisco Systems, Inc.
Email: tsaad.net@gmail.com
Kiran Makhijani
Futurewei Technologies
Email: kiranm@futurewei.com
Haoyu Song
Futurewei Technologies
Email: haoyu.song@futurewei.com
Greg Mirsky
Ericsson
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Email: gregimirsky@gmail.com
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