MPLS Working Group M. Bocci
Internet-Draft Nokia
Intended status: Informational S. Bryant
Expires: April 17, 2022 University of Surrey 5GIC
October 14, 2021
Requirements for MPLS Label Stack Indicators for Ancillary Data
draft-bocci-mpls-miad-adi-requirements-00
Abstract
This draft specifies requirements for indicators in the MPLS label
stack of ancillary data that exists below the label stack. This work
is the product of the IETF MPLS Open Design Team. Requirements are
derived from a number of new 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, based on application
data that may be in or below the bottom of the label stack.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 April 17, 2022.
Copyright Notice
Copyright (c) 2021 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 . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 3
2. MPLS Ancillary Data Indicator Requirements . . . . . . . . . 4
2.1. General Requirements . . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
There is significant interest in developing the MPLS data plane to
address the requirements of new applications. These applications
typically include ancillary data that is contained in or below the
label stack. There is a requirement for this data to be either
intercepted and processed, or some other forwarding decision to be
made. This makes use of mechanisms implemented by an intermediate or
egress label switching router (LSR) that complies with the MPLS base
architecture and potentially its extensions, including (but not
limited to) [RFC3031], [RFC3032], [RFC6790].
This draft specifies requirements for indicators in the MPLS label
stack to support these applications.
1.1. Terminology
o Ancillary Data: Data relating to the MPLS packet that may be used
to affect the forwarding or other processing of that packet,
either at the LER or LSR. This data may be implicit (i.e.
context-specific), encoded withing the label stack (in-stack
data), after the bottom of the label stack but not considered a
part of the payload, or within the payload.
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o In-Stack: Any location within the MPLS label stack including the
outer label and the bottom of stack (the label with the S-bit
set).
o Ancillary Data Indicator (ADI): A indicator in the MPLS label
stack that ancillary data exists in this packet. It may also
indicate the specific type of the ancillary data.
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-mulitipoint layer 2 and layer 3 services. An overview
of the development of MPLS is provided in
[I-D.bryant-mpls-dev-primer].
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 ancillary data is
carried in MPLS and how its presence is indicated to the LSR or
egress LER, for example In-situ OAM and Service Function Chaining
(SFC). A summary of these proposals is contained
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in[I-D.bryant-mpls-dev-primer], an overview of use cases is provided
in [Reference to MIAD use cases].[I-D.song-mpls-extension-header]
summarises some of the issues with existing solutions to address
these new applications:
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 applications therefore require the definition of extensions to
the MPLS architecture and label stack operations that can be used
across these applications in order to minimise implemention
complexity and promote interoperability.
2. MPLS Ancillary Data Indicator Requirements
This document specifies requirements of MPLS Indicators for
Ancilliary Data (MIAD). The requirements are for the behavior of the
protocol mechanisms and procedures that constitute building blocks
out of which mechanisms for indicating ancilliary data that exists in
the MPLS payload using the MPLS label stack (so-called in-stack
indicators) are constructed. It does not specify the detailed
processing that may be required by an application of that ancilliary
data by an LSR. The requirements in this document do not describe
what functions MIAD implementation supports. 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.
2.1. General Requirements
o 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.
o Any solutions to these requirements MUST not restrict the
generality of MPLS architecture.
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o Any solution MUST respect the principle that Special Purpose
Labels are the mechanism of last resort.
o Solutions MUST be able to coexist with and not obsolete existing
MPLS mechanisms.
o Neither an ADI or ancilliary data must be delivered to a node that
is not capable of processing it.
o Care needs to be taken in the coeistence of ancillary data and
existing post-stack data mechanisms.
o Mechanisms are required to determine that all nodes that need to
process the ancillary data can read the required distance into the
packet at that node.
o A mechanism is REQUIRED for Ancilliary Data Indicators to indicate
the presence of ancilliary data in the MPLS label stack (Ed. note:
This is similar to ELI).
o A mechanism is REQUIRED for Ancilliary Data Indicators to indicate
the presence of ancilliary data below the MPLS label stack (Ed.
note: this is similar to GAL/G-ACH).
o The mechanism to indicate that Ancilliary Data is present MUST
operate in the context of the top of stack LSE.
o Ancilliary data may be associated with control or maintenance
information for traffic carried by an LSP, or it may be associated
with the user traffic itself.
o Ancilliary Data Indicators (ADIs) SHOULD make use of existing MPLS
data plane operations. If extensions to the MPLS data plane are
required, they MUST NOT be inconsitent with the MPLS architecture.
o A mechanism is REQUIRED to enable an LER inserting ADIs to
determine whether LSRs along the path can parse the label stack
and process the ADI at the location it is inserted.
o A mechanism is REQUIRED to enable an LER inserting ADIs to
determine if the ADI will be processed by LSRs along the path.
o A mechanism is REQUIRED to enable an LER inserting ADIs to
determine if the far-end LER can accept and process a packet
containing a given ADI.
o ADIs SHOULD be supported for both P2P and P2MP paths, but any
specific ADI may only be supported for one or the other.
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o Data plane mechanisms for ADIs MUST be independent of the control
plane type (LDP, RSVP, BGP, static, IGP, etc).
o A mechanism MUST be defined for control planes (LDP, RSVP, BGP,
static, IGP, etc) to determine the ability of downstream LSRs/LERs
to accept/process a given ADI.
o A mechanism is REQUIRED to enable an LSR to efficiently determine
if an ADI is present in a packet.
o ADIs can only be inserted at LERs, but may be processed at LSRs
and LERs. If it is required to insert an ADI at a transit router
on an LSP, then a new label stack must be pushed. .
o It SHOULD be possible to include indicators for ancillary data for
multiple applications in the same packet, but each ADI only
supports one application.
o It MUST be possible to insert new ADIs for new applications on the
same LSP.[Ed note: neet to clarify]
o The solution must allow ADI and non-ADI packets to coexist on the
same LSP.
o The solution must support the processing of a subset of the ADIs
on a packet.
o The solution MUST support slow path processing of ancilliary data.
o The solution MUST support fast path processing of ancilliary data.
o The solution MUST support hop-by-hop processing of ancilliary
data.
o The solution MUST support end-to-end processing of ancilliary
data.
o If both hop-by-hop and and end-to-end ancilliary data indicators
are present together, the prescendence must be specified in the
design.
o In order to prevent unnecesary scanning of the packet, care needs
to be taken in the location of the ancillary data, for example it
should be located as close to the label stack as possible.
o A solition must be provided to verify the authenticity of
ancillary data processed to LSRs.
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o The design of the ADIs and ancillary data must not expose
confidential information to the LSRs.
3. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
4. Security Considerations
The mechanisms required by this document introduce new security
considerations to MPLS. It is expected that individual solutions
meeting these requirements will address any security considerations.
5. Acknowledgements
The authors gratefully acknowledge the input of the members of the
MPLS Open Design Team.
6. References
6.1. 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>.
6.2. Informative References
[I-D.bryant-mpls-dev-primer]
Bryant, S., "A Primer on the Development of MPLS", draft-
bryant-mpls-dev-primer-00 (work in progress), March 2021.
[]
Song, H., Li, Z., Zhou, T., Andersson, L., and Z. Zhang,
"MPLS Extension Header", draft-song-mpls-extension-
header-05 (work in progress), July 2021.
[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>.
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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/info/rfc3032>.
[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>.
[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/info/rfc6790>.
Authors' Addresses
Matthew Bocci
Nokia
Email: matthew.bocci@nokia.com
Stewart Bryant
University of Surrey 5GIC
Email: sb@strewartbryant.com
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