MPLS Working Group M. Bocci, Ed.
Internet-Draft Nokia
Intended status: Informational S. Bryant
Expires: 28 September 2023 University of Surrey 5GIC
J. Drake
Juniper Networks
27 March 2023
Requirements for MPLS Network Actions
draft-ietf-mpls-mna-requirements-05
Abstract
This document specifies requirements for MPLS network actions which
affect the forwarding or other processing of MPLS packets. These
requirements are derived from a number of proposals for additions to
the MPLS label stack to allow forwarding or other processing
decisions to be made, either by a transit or terminating LSR (i.e.
the LER).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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 28 September 2023.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. MPLS Network Action Requirements . . . . . . . . . . . . . . 5
3.1. General Requirements . . . . . . . . . . . . . . . . . . 5
3.2. Requirements on the MNA Sub-Stack Indicator . . . . . . . 6
3.3. Requirements on Network Action Indicators . . . . . . . . 6
3.4. Requirements on Ancillary Data . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
There is significant interest in developing the MPLS data plane to
address the requirements of new use cases
[I-D.saad-mpls-miad-usecases], which require a general mechanism,
termed MPLS network actions, for enhanced forwarding or other
processing of MPLS packets. It is intended that this mechanism will
be conformant to the greatest extent possible with the existing MPLS
architecture as specified by, among other documents, [RFC3031],
[RFC3032], and [RFC6790].
This document specifies the requirements for MPLS network actions, as
well as the encoding and use of the ancillary data.
1.1. Terminology
* Network Action: An operation to be performed on a packet or as a
consequence of a packet being processed by a router. A network
action may affect router state, packet forwarding, or it may
affect the packet in some other way. Ed.>Need to cross check with
framework draft
* Network Action Indication (NAI): An indication in the packet that
a certain network action is to be performed.
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* Ancillary Data (AD): Data in an MPLS packet associated with a
given Network Action that may be used as input to the processing
of the Network Action or results from the processing of the
Network Action.
* In-Stack Data: Ancillary data carried within the MPLS label stack.
* Post-Stack Data: Ancillary data carried in a packet between the
bottom of the MPLS label stack and the first octet of the user
payload. This document does not prescribe whether post-stack data
precedes or follows any other protocol structure such as a control
word or associated channel header (ACH).
* Scope: The set of nodes that should perform a given action.
1.2. Background
The MPLS architecture is specified in [RFC3031] and provides a
mechanism for forwarding packets through a network without requiring
any analysis of the packet payload's network layer header by
intermediate nodes (Label Switching Routers - LSRs). Formally,
inspection may only occur at network ingress (the Label edge router -
LER) where the packet is assigned to a forwarding equivalence class
(FEC).
MPLS uses switching based on a label pushed on the packet to achieve
efficient forwarding and traffic engineering of flows associated with
the FEC. While originally used for IP traffic, MPLS has been
extended to support point-to-point, point-to-multipoint and
multipoint-to-multipoint layer 2 and layer 3 services. An overview
of the development of MPLS is provided in
[I-D.bryant-mpls-dev-primer].
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A number of applications have emerged which require LSRs to make
forwarding or other processing decisions based on inspection of the
network layer header, or some other ancillary information in the
protocol stack encapsulated deeper in the packet. An early example
of this was generation of a hash of the payload header to be used for
load balancing over Equal Cost Multipath (ECMP) or Link Aggregation
Group (LAG) next hops. This is based on an assumption that the
network layer protocol is IP. MPLS was extended to avoid the need
for LSRs to perform this operation if load balancing was needed based
on the payload and instead use only the MPLS label stack, using the
Entropy Label / Entropy Label Indicator [RFC6790] which are inserted
at the LER. Other applications where the intermediate LSRs may need
to inspect and process a packet on an LSP include OAM, which can make
use of mechanisms such the Router Alert Label [RFC3032] or the
Generic Associated Channel Label (GAL) [RFC5586] to indicate that an
intercepted packet should be processed locally. See
[I-D.bryant-mpls-dev-primer] for detailed list of such applications.
There have been a number of new proposals for how network actions and
associated ancillary data is to be carried in MPLS and how its
presence is indicated to the LSR or egress LER, for example In-situ
OAM [I-D.gandhi-mpls-ioam-sr] and Service Function Chaining (SFC)
[RFC7665]. A summary of these proposals is contained in
[I-D.bryant-mpls-dev-primer], and an overview of use cases is
provided in [I-D.saad-mpls-miad-usecases].
[I-D.song-mpls-extension-header] discusses some of the issues with
these proposals (note that this document draws on the requirements
and issues without endorsing a specific solution from
[I-D.song-mpls-extension-header]):
These solutions rely on either the built-in next-protocol
indicator in the header or the knowledge of the format and size of
the header to access the following packet data. The node is
required to be able to parse the new header, which is unrealistic
in an incremental deployment environment.
A piecemeal solution often assumes the new header is the only
extra header and its location in the packet is fixed by default.
It is impossible or difficult to support multiple new headers in
one packet due to the conflicted assumption. An example of this
is that the GAL/G-ACH mechanism assumes that if the GAL is
present, only a single G-ACH header follows.
New use cases therefore require the definition of extensions to the
MPLS architecture and label stack operations that can be used across
these use cases in order to minimise implementation complexity and
promote interoperability and extensibility.
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2. 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.
Although this document is not a protocol specification, this
convention is adopted for clarity of description of requirements.
3. MPLS Network Action Requirements
This document specifies requirements of MPLS Network Action (MNA)
Indicators (NAIs), and the associated Ancillary Data, as well as the
alert mechanism (the MPLS Network Action Sub-Stack Indicator) to
indicate to an LSR or LER that NAIs are present in a packet. The
requirements are for the behavior of the protocol mechanisms and
procedures that constitute building blocks out of which indicators
for network actions and associated ancillary data are constructed.
It does not specify the detailed actions and processing of any
network actions or ancillary data by an LSR or LER. The purpose of
this document is to identify the toolkit and any new protocol work
that is required. This new protocol work MUST be based on the
existing MPLS architecture.
3.1. General Requirements
1. MPLS combines extensibility, flexibility and efficiency by using
control plane context combined with a simple data plane
mechanism to allow the network to make forwarding decisions
about a packet. Any solution MUST maintain these properties of
MPLS.
2. Any MNA solutions to these requirements MUST NOT restrict the
generality of MPLS architecture [RFC3031], [RFC3032].
3. If extensions to the MPLS data plane are required, they MUST NOT
be inconsistent with the MPLS architecture [RFC3031], [RFC3032].
4. MNA solutions meeting the requirements set out in this document
MUST be able to coexist with and MUST NOT obsolete existing MPLS
mechanisms.
5. The design of any MNA solution SHOULD be such that an LSR is
able to efficiently parse the label stack.
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6. Any MNA solution specification MUST discuss the ECMP
consequences of the design.
7. MNA solutions MUST NOT increase the size of the MPLS label stack
more than is necessary.
8. The design of any MNA solution MUST NOT expose confidential
information [RFC6973] [RFC3552] to the LSRs.
9. Any MNA solution specification MUST document any changes to the
existing MPLS data plane security model that it introduces.
10. An MNA solution MUST allow NAI-carrying and non-NAI-carrying
packets to coexist on the same LSP.
3.2. Requirements on the MNA Sub-Stack Indicator
1. An MNA solution MUST define how a node determines whether Network
Action Indicators (NAIs) are present in the packet.
2. If NAIs are required, an MNA solution MUST specify where they are
to be placed in the packet i.e. in-stack or post-stack.
3. An MNA solution MUST respect the principle that Special Purpose
Labels are the mechanism of last resort and therefore must
minimise the number of new SPLs that are allocated.
3.3. Requirements on Network Action Indicators
1. Insertion, parsing, processing and disposition of NAIs SHOULD
make use of existing MPLS data plane operations.
2. An NAI MUST NOT be delivered to a node that is not capable of
processing the indicated network action in a way that is
acceptable to the imposing LER.
3. An MNA solution MUST enable a node inserting or modifying NAIs
to determine if the far-end LER can accept and process a packet
containing a given NAI.
4. The NAI design MUST support scoping of network actions.
5. A given NAI specification MUST specify if the scope is end-to-
end, hop-by-hop, or directed at one or more selected nodes.
6. If an MNA solution allows more than one scope, it MUST provide a
mechanism to specify the precedence of the scopes.
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7. An MNA solution should support NAIs for both P2P and P2MP paths,
but any specific NAI MAY only be supported for one or the other.
8. An MNA solution defining data plane mechanisms for NAIs MUST be
consistent across different control plane protocol types.
9. An MNA solution MUST allow the in-use control / management
planes to determine the ability of downstream LSRs/LERs to
accept/process a given NAI.
10. An MNA solution SHOULD allow indicators for multiple network
actions in the same packet.
11. An MNA solution MUST support the processing of a subset of the
NAIs on a packet.
12. NAIs are normally inserted at LERs, but MAY be processed at LSRs
and LERs.
13. If an network action needs to insert an NAI with in-stack
ancillary data at an LSR on an LSP, then the new network action
indicator and any required ancillary data MUST be pushed onto
the MPLS label stack.
14. If a network action needs to insert an NAI with below stack
ancillary data at an LSR on an LSP, then the MNA solution
specification MUST specify how this is achieved in all
circumstances and MUST be consistent with {RFC3031}.
15. MPLS network action specifications MUST specify if in-stack or
post-stack ancillary data can be rewritten by an LSR.
16. An MPLS network action specification MUST specify whether
ancillary data is required and whether it is in-stack and/or
post-stack.
17. Network action indicators must be allocated through the IANA
process specified in the MNA solution specification.
18. Is it RECOMENDED that an MPLS network action specification
supports network actions for private use [RFC8126].
19. A node removing an NAI MUST NOT leave the MPLS label stack in
such a way that downstream nodes are unable to determine the
presence of ancillary data remaining in the packet.
3.4. Requirements on Ancillary Data
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1. Solutions for in-stack ancillary data MUST be able to coexist
with and MUST NOT obsolete existing MPLS mechanisms. Such
solutions MUST be described in a standards track RFC.
2. Specifications for MNA solutions that use in-stack ancillary
data MUST justify why they require in-stack ancillary data.
3. MNA solutions MUST take care to limit the quantity of in-stack
ancillary data to the minimum amount required.
4. A common preamble for ancillary data MUST be defined so that a
node receiving the ancillary data can determine whether to
process, ignore, skip over or discard it according to network or
local policies.
5. A standardised container MUST be defined for in-stack ancillary
data based on the MPLS LSE.
6. Any MNA solution specification MUST describe whether it can
coexist with existing post-stack data mechanisms e.g. control
words and G-ACH, and if so how this coexistence operates.
7. An MNA solution MUST allow an LER inserting ancillary data to
determine that each node that needs to process the ancillary
data can read the required distance into the packet at that
node, for example [RFC9088].
8. In order to prevent unnecessary scanning of the packet, care
needs to be taken in the location of any post stack ancillary
data, for example it SHOULD be located as close to the bottom of
the label stack as possible.
9. Ancillary data MAY be associated with control or maintenance
information for traffic carried by an LSP, and/or it MAY be
associated with the user traffic itself.
10. For scoped ancillary data, any MNA solution MUST allow an LER
inserting NAIs whose network actions make use of that ancillary
data to determine if the NAI and ancillary data will be
processed by LSRs within the scope along the path. Such a
solution MAY need to determine if LSRs along the path can
process a specific type of AD implied by the NAI at the depth in
the stack that it will be presented to the LSR.
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11. MNA solution specifications MUST specify if the ancillary data
needs to be processed as a part of the immediate forwarding
operation and whether packet mis-ordering is allowed to occur as
a result of the time taken to process the ancillary data. Ed.
We think this applies to both NAs and ancillary data and should
be generalised.
12. A solution MUST be provided to verify the authenticity of
ancillary data processed to LSRs [RFC3552].
13. The design of the ancillary data MUST NOT expose confidential
information [RFC6973] [RFC3552] to the LSRs.
14. A mechanism MUST exist to notify an egress LER of the presence
of ancillary data so that it can dispose of it appropriately.
15. An egress LER MUST NOT forward a packet with ancillary data to a
node that is not expecting the ancillary data to be present.
4. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
5. Security Considerations
The mechanisms required by this document introduce new security
considerations to MPLS. Individual solution specifications meeting
these requirements MUST address any security considerations.
6. Acknowledgements
The authors gratefully acknowledge the contributions from Greg
Mirsky, Yingzhen Qu, Haoyu Song, Tarek Saad, Loa Andersson, Tony Li,
Adrian Farrel, Jie Dong and Bruno Decraene, and participants in the
MPLS working group who have provided comments.
The authors also gratefully acknowledge the input of the members of
the MPLS Open Design Team.
7. References
7.1. Normative References
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[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/rfc/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/rfc/rfc8174>.
7.2. Informative References
[I-D.bryant-mpls-dev-primer]
Bryant, S., "A Primer on the Development of MPLS", Work in
Progress, Internet-Draft, draft-bryant-mpls-dev-primer-02,
9 May 2022, <https://datatracker.ietf.org/doc/html/draft-
bryant-mpls-dev-primer-02>.
[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://datatracker.ietf.org/doc/html/draft-gandhi-mpls-
ioam-sr-06>.
[I-D.saad-mpls-miad-usecases]
Saad, T., Makhijani, K., Song, H., and G. Mirsky, "Use
Cases for MPLS Network Action Indicators and MPLS
Ancillary Data", Work in Progress, Internet-Draft, draft-
saad-mpls-miad-usecases-02, 20 April 2022,
<https://datatracker.ietf.org/doc/html/draft-saad-mpls-
miad-usecases-02>.
[]
Song, H., Zhou, T., Andersson, L., Zhang, Z. J., and R.
Gandhi, "MPLS Network Actions using Post-Stack Extension
Headers", Work in Progress, Internet-Draft, draft-song-
mpls-extension-header-11, 15 October 2022,
<https://datatracker.ietf.org/doc/html/draft-song-mpls-
extension-header-11>.
[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/rfc/rfc3031>.
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[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/rfc/rfc3032>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/rfc/rfc3552>.
[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/rfc/rfc5586>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/rfc/rfc6790>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/rfc/rfc6973>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/rfc/rfc7665>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC9088] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", RFC 9088,
DOI 10.17487/RFC9088, August 2021,
<https://www.rfc-editor.org/rfc/rfc9088>.
Authors' Addresses
Matthew Bocci (editor)
Nokia
Email: matthew.bocci@nokia.com
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Stewart Bryant
University of Surrey 5GIC
Email: sb@stewartbryant.com
John Drake
Juniper Networks
Email: jdrake@juniper.com
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