MPLS Working Group M. Vigoureux, Ed.
Internet-Draft Alcatel-Lucent
Intended status: Standards Track D. Ward, Ed.
Expires: December 30, 2009 Cisco Systems, Inc.
M. Betts, Ed.
Huawei
June 28, 2009
Requirements for OAM in MPLS Transport Networks
draft-ietf-mpls-tp-oam-requirements-02
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Abstract
This document lists the requirements for the Operations,
Administration and Maintenance functionality of MPLS Transport
Profile. These requirements apply to pseudowires, Label Switched
Paths, and Sections. Architectural and functional requirements are
covered in this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language and Terminology . . . . . . . . . . 4
2. OAM Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Architectural Requirements . . . . . . . . . . . . . . . . 5
2.1.1. Scope of OAM . . . . . . . . . . . . . . . . . . . . . 5
2.1.2. Independence . . . . . . . . . . . . . . . . . . . . . 5
2.1.3. Addressing, Routing and Forwarding . . . . . . . . . . 6
2.1.4. Interoperability and Interworking . . . . . . . . . . 6
2.1.5. Data Plane . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Functional Requirements . . . . . . . . . . . . . . . . . 7
2.2.1. General Requirements . . . . . . . . . . . . . . . . . 8
2.2.2. Continuity Checks . . . . . . . . . . . . . . . . . . 8
2.2.3. Connectivity Verifications . . . . . . . . . . . . . . 8
2.2.4. Diagnostic . . . . . . . . . . . . . . . . . . . . . . 8
2.2.5. Route Tracing . . . . . . . . . . . . . . . . . . . . 9
2.2.6. Lock Instruct . . . . . . . . . . . . . . . . . . . . 9
2.2.7. Lock Reporting . . . . . . . . . . . . . . . . . . . . 9
2.2.8. Alarm Reporting . . . . . . . . . . . . . . . . . . . 10
2.2.9. Remote Defect Indication . . . . . . . . . . . . . . . 10
2.2.10. Client Failure Indication . . . . . . . . . . . . . . 10
2.2.11. Packet Loss . . . . . . . . . . . . . . . . . . . . . 10
2.2.12. Delay Measurement . . . . . . . . . . . . . . . . . . 11
3. Congestion Considerations . . . . . . . . . . . . . . . . . . 11
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
In the context of MPLS Transport Profile (MPLS-TP, see [5] and [6]),
the rationales for Operations, Administration and Maintenance (OAM)
mechanisms are twofold as they can serve:
o as a network-oriented mechanism (used by a transport network
operator) to monitor his network infrastructure and to implement
internal mechanisms in order to enhance the general behaviour and
the level of performance of his network (e.g., protection
mechanism in case of node or link failure). For example, fault
localization is typically associated with this use case.
o as a service-oriented mechanism (used by a transport service
provider) to monitor services offered to end customers in order to
be able to react rapidly in case of a problem and to be able to
verify some of the Service Level Agreements (SLAs) parameters
(e.g., using performance monitoring) negotiated with the end
customers. Note that a transport service could be provided over
several networks or administrative domains that may not all be
owned and managed by the same transport service provider.
More generally, OAM is an important and fundamental functionality in
transport networks as it contributes to:
o the reduction of operational complexity and costs, by allowing for
efficient and automatic detection, localisation, handling, and
diagnosis of defects, and by minimizing service interruptions and
operational repair times.
o the enhancement of network availability, by ensuring that defects,
for example resulting in misdirected customer traffic, and faults,
are detected, diagnosed and dealt with before a customer reports
the problem.
o meet service and performance objectives, as the OAM functionality
allows for SLA verification in a multi-maintenance domain
environment and allows for the determination of service
degradation due, for example, to packet delay or packet loss.
This document lists the requirements for the OAM functionality of
MPLS-TP. These requirements apply to pseudowires (PWs), Label
Switched Paths (LSPs), and Sections.
These requirements are derived from the set of requirements specified
by ITU-T and published in the ITU-T Supplement Y.Sup4 [7].
By covering transport specificities, these requirements complement
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those identified in RFC 4377 [8].
Note that the OAM functionalities identified in this document may be
used for fault management, performance monitoring and/or protection
switching applications. For example, connectivity verification can
be used for fault management application by detecting failure
conditions, but may also be used for performance monitoring
application through its contribution to the evaluation of performance
metrics (e.g., unavailability time). Nevertheless, it is outside the
scope of this document to specify which functionality should be used
for which application.
1.1. Requirements Language and Terminology
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 [1].
In this document we refer to the inability of a function to perform a
required action, as a fault. This does not include an inability due
to preventive maintenance, lack of external resources, or planned
actions. See also ITU-T G.806 [2].
In this document we refer to the situation in which the density of
anomalies has reached a level where the ability to perform a required
function has been interrupted, as a defect. See also ITU-T G.806
[2].
In this document we refer to a Label Edge Router (LER), for a given
LSP or Section, and to a PW Terminating Provider Edge (T-PE), for a
given PW, as an End Point. Further, we refer to a Label Switching
Router (LSR), for a given LSP, and to a PW Switching Provider Edge
(S-PE), for a given PW, as an Intermediate Point. This document does
not make a distinction between End Points (e.g., source and
destination) as it can be inferred from the context of the sentences.
In this document we use the term "node" as a general reference to End
Points and Intermediate Points.
In this document we refer to both segment and concatenated segments
as segments (see [6] for definitions relating to the term "segment"
as well as for other definitions relating to MPLS-TP).
2. OAM Requirements
This section lists the requirements by which the OAM functionality of
MPLS-TP should abide. Note that some requirements for this
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application of MPLS are similar to some of those listed in RFC 4377
[8].
The requirements listed below may be met by one or more OAM
protocols; the definition or selection of these protocols is outside
the scope of this document.
2.1. Architectural Requirements
2.1.1. Scope of OAM
The protocol solutions developed to meet the requirements identified
in this document MUST be applicable to point-to-point bidirectional
PWs, point-to-point bidirectional LSPs, and point-to-point
bidirectional Sections and SHOULD additionaly be applicable to
unidirectional point-to-point and point-to-multipoint LSPs.
The service emulated by a single segment or a multi-segment PW may
span multiple domains. An LSP may also span multiple domains. It
MUST be possible to operate OAM functions on a per domain basis.
More generally, the protocol solutions MUST be applicable end-to-end
and to segments.
Since LSPs may be stacked, the protocol solutions MUST be applicable
on any LSP, regardless of the label stack depth. Furthermore it MUST
be possible to estimate OAM fault and performance metrics of a single
PW or LSP segment or of an aggregate of PWs or LSPs segments.
2.1.2. Independence
The protocol solutions SHOULD be independent of the underlying
tunnelling or point-to-point technology or transmission media.
The protocol solutions SHOULD be independent of the service a PW may
emulate.
Any OAM function operated on a PW, LSP or Section SHOULD be
independent of the OAM function(s) operated on a different PW, LSP or
Section. In other words, only the OAM functions operated on e.g., a
given LSP should be used to achieve the OAM objectives for that LSP.
Note that independence should not be understood here in terms of
isolation as there can be interactions between OAM functions operated
on e.g., an LSP, and on another LSP or a PW.
Likewise, any OAM function applied to segment(s) of a PW or LSP
SHOULD be independent of the OAM function(s) operated on the end-to-
end PW or LSP. It SHOULD also be possible to distinguish an OAM
packet running over a segment of a PW or LSP from another OAM packet
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running on the end-to-end PW or LSP. Furthermore, any OAM function
applied to segment(s) of a PW or LSP SHOULD be independent of the OAM
function(s) applied to other segment(s) of the same PW or LSP.
Finally, the protocol solutions MUST support the capability to be
concurrently and independently operated end-to-end and on segments.
OAM functions MUST operate and be configurable even in the absence of
a control plane. Conversely, it SHOULD be possible to enable/disable
the capability to operate OAM functions as part of connectivity
management and it SHOULD also be possible to enable/disable the
capability to operate OAM functions after connectivity has been
established. In the latter case, the customer MUST NOT perceive
service degradation as a result of OAM enabling/disabling. Ideally
OAM enabling/disabling should take place without introducing any
customer impairments (e.g., no customer packet losses). Procedures
aimed to prevent any traffic impairment MUST be defined for the
enabling/disabling of OAM functions. Means for configuring OAM
functions and for connectivity management are outside the scope of
this document.
2.1.3. Addressing, Routing and Forwarding
The OAM functionality may be deployed in a variety of environments.
o In some environments (e.g., IP/MPLS environments), IP routing and
forwarding capabilities are inherently present in the forwarding
plane. In this case, it MUST be possible to operate the OAM
functions by relying on IP routing and forwarding capabilities.
o In some environments (e.g., MPLS-TP environments), IP routing and
forwarding capabilities may not necessarily be present in the user
plane. In this case, it MUST be possible to operate the OAM
functions without relying on IP routing and forwarding
capabilities.
In cases where OAM messages need to incorporate identification
information (e.g., source and/or destination nodes), the protocol
solution(s) MUST at least support an IP addressing structure and MUST
also be extensible to support additional identification schemes.
2.1.4. Interoperability and Interworking
It is REQUIRED that OAM interoperability is achieved across the
environments described in Section 2.1.3. It is also REQUIRED that
the two first requirements of Section 2.1.3 still hold and MUST still
be met when interoperability is achieved.
When MPLS-TP is run with IP routing and forwarding capabilities, it
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MUST be possible to operate any of the existing IP/MPLS and PW OAM
protocols (e.g., LSP-Ping [3], MPLS-BFD [9], VCCV [4] and VCCV-BFD
[10]).
2.1.5. Data Plane
OAM functions operate in the data plane. OAM packets MUST run in-
band; that is, OAM packets for a specific PW, LSP or Section MUST
follow the exact same data path as user traffic of that PW, LSP or
Section. This is often referred to as fate sharing.
It MUST be possible to discriminate user traffic from OAM packets.
This includes a means to differentiate OAM packets from user traffic
as well as the capability to apply specific treatment to OAM packets,
at the nodes targeted by these OAM packets.
As part of the design of OAM protocol solution(s) for MPLS-TP, a
mechanism, for enabling the encapsulation and differentiation of OAM
messages on a PW, LSP or Section, MUST be provided. Such mechanism
SHOULD also support the encapsulation and differentiation of existing
IP/MPLS and PW OAM messages.
2.2. Functional Requirements
Hereafter are listed the required functionalities composing the
MPLS-TP OAM toolset. The list may not be exhaustive and as such the
OAM mechanisms developed in support of the identified requirements
SHALL be extensible and thus SHALL NOT preclude the definition of
additional OAM functionalities, in the future.
The design of OAM mechanisms for MPLS-TP, MUST allow for the ability
to support experimental OAM functions. These functions MUST be
disabled by default.
The use of any OAM function MUST be optional and it MUST be possible
to choose which OAM function(s) to use and on which PW, LSP or
Section to apply it(them) to.
It is RECOMMENDED that the protocol solution, meeting one or more
functional requirement(s), be the same for PWs, LSPs and Sections.
It is RECOMMENDED that the protocol solution, meeting one or more
functional requirement(s), effectively provides a fully featured
function; that is, a function which is applicable to all the cases
identified for that functionality. In that context, protocol
solution(s) MUST state their applicability.
Unless otherwise stated, the OAM functionalities MUST NOT rely on
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user traffic; that is, only OAM messages MUST be used to achieve the
objectives.
2.2.1. General Requirements
If a defect or fault occurs on a PW, LSP or Section, mechanisms MUST
be provided to detect it, diagnose it, localize it, and notify the
appropriate nodes. Mechanisms SHOULD exist such that corrective
actions can be taken.
Furthermore, mechanisms MUST be available for a service provider to
be informed of a fault or defect affecting the service(s) it
provides, even if the fault or defect is located outside of his
domain.
The protocol solution(s) developed to meet these requirements may
rely on information exchange. Information exchange between various
nodes involved in the operation of an OAM function SHOULD be reliable
such that, for example, defects or faults are properly detected or
that state changes are effectively known by the appropriate nodes.
2.2.2. Continuity Checks
The MPLS-TP OAM toolset MUST provide functionality to enable the
verification of the continuity of a PW, LSP or Section.
This function SHOULD be performed between End Points of PWs, LSPs and
Sections.
This function SHOULD be performed pro-actively.
2.2.3. Connectivity Verifications
The MPLS-TP OAM toolset MUST provide functionality to enable the
verification of the connectivity of a PW, LSP or Section.
This function SHOULD be performed between End Points and Intermediate
Points of PWs and LSPs, and between End Points of PWs, LSPs and
Sections.
This function SHOULD be performed on-demand. This function SHOULD be
performed pro-actively only between End Points of PWs, LSPs and
Sections.
2.2.4. Diagnostic
The MPLS-TP OAM toolset MAY provide functionality to enable the
conduction of diagnostic tests on a PW, LSP or Section. An example
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of such diagnotic test would consist in looping the traffic at an
Intermediate Point, back to the End Point it originates from.
Another example of such diagnotic test would consist in estimating
the bandwidth of e.g., an LSP.
This function SHOULD be performed on-demand.
This function SHOULD be performed between End Points and Intermediate
Points of PWs and LSPs, and between End Points of PWs, LSPs and
Sections.
2.2.5. Route Tracing
The MPLS-TP OAM toolset MUST provide functionality to enable an End
Point to discover the Intermediate (if any) and End Point(s) along a
PW, LSP or Section, and more generaly to trace the route of a PW, LSP
or Section. The information collected MUST include identifiers
related to the nodes and interfaces composing that route.
This function SHOULD be performed on-demand.
This function SHOULD be performed between End Points and Intermediate
Points of PWs and LSPs, and between End Points of PWs, LSPs and
Sections.
2.2.6. Lock Instruct
The MPLS-TP OAM toolset MUST provide functionality to enable an End
Point of a PW, LSP or Section to instruct its associated End Point(s)
to lock the PW, LSP or Section. Note that lock corresponds to an
administrative status in which forwarding traffic on and from the PW,
LSP or Section is disabled.
This function SHOULD be performed on-demand.
This function SHOULD be performed between End Points of PWs, LSPs and
Sections.
2.2.7. Lock Reporting
The MPLS-TP OAM toolset MUST provide functionality to enable an
Intermediate Point of a PW or LSP to report, to an End Point of that
same PW or LSP, an external lock condition affecting that PW or LSP.
This function SHOULD be performed pro-actively.
This function SHOULD be performed between Intermediate Points and End
Points of PWs and LSPs.
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2.2.8. Alarm Reporting
The MPLS-TP OAM toolset MUST provide functionality to enable an
Intermediate Point of a PW or LSP to report, to an End Point of that
same PW or LSP, a fault or defect condition affecting that PW or LSP.
This function SHOULD be performed pro-actively.
This function SHOULD be performed between Intermediate Points and End
Points of PWs and LSPs.
2.2.9. Remote Defect Indication
The MPLS-TP OAM toolset MUST provide functionality to enable an End
Point to report, to its associated End Point, a fault or defect
condition that it detects on a PW, LSP or Section for which they are
the End Points.
This function SHOULD be performed pro-actively.
This function SHOULD be performed between End Points of PWs, LSPs and
Sections.
2.2.10. Client Failure Indication
The MPLS-TP OAM toolset MUST provide functionality to enable the
propagation, across an MPLS-TP network, of information pertaining to
a client defect of fault condition detected at an End Point of a PW
or LSP, if the client layer OAM mechanisms do not provide an alarm
notification/propagation mechanism.
This function SHOULD be performed pro-actively.
This function SHOULD be performed between End Points of PWs and LSPs.
2.2.11. Packet Loss
The MPLS-TP OAM toolset MUST provide functionality to enable the
quantification of packet loss ratio over a PW, LSP or Section.
Note that packet loss ratio is the ratio of the user packets not
delivered to the total number of user packets transmitted during a
defined time interval. The number of user packets not delivered is
the difference between the number of user packets transmitted by an
End Point and the number of user packets received at an End Point.
This function MAY either be performed pro-actively or on-demand.
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This function SHOULD be performed between End Points of PWs, LSPs and
Sections.
It SHOULD be possible to rely on user-plane traffic to achieve that
functionality.
2.2.12. Delay Measurement
The MPLS-TP OAM toolset MUST provide functionality to enable the
quantification of the one-way, and if appropriate, the two-way, delay
of a PW, LSP or Section.
o One-way delay is the time elapsed from the start of transmission
of the first bit of a packet by an End Point until the reception
of the last bit of that packet by the other End Point.
o Two-way delay is the time elapsed from the start of transmission
of the first bit of a packet by a End Point until the reception of
the last bit of that packet by the same End Point, when loopback
is performed at the other End Point.
This function SHOULD be performed on-demand and MAY be perform pro-
actively.
This function SHOULD be performed between End Points of PWs, LSPs and
Sections.
It SHOULD be possible to rely on user-plane traffic to achieve that
functionality.
3. Congestion Considerations
A mechanism (e.g., rate limiting) MUST be provided to prevent OAM
packets from causing congestion in the PSN.
4. Security Considerations
This document, as itself, does not imply any security consideration
but OAM, as such, is subject to several security considerations. OAM
messages can reveal sensitive information such as passwords,
performance data and details about e.g., the network topology.
The nature of OAM therefore suggests having some form of
authentication, authorization and encryption in place. This will
prevent unauthorized access to MPLS-TP equipment and it will prevent
third parties from learning about sensitive information about the
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transport network.
In general, mechanisms SHOULD be provided to ensure that OAM
functions cannot be accessed unauthorized.
Further, OAM messages MAY be authenticated to prove their origin and
to make sure that they are destined for the receiving node.
An OAM packet received over a PW, LSP or Section MUST NOT be
forwarded beyond the End Point of that PW, LSP or Section, so as to
avoid that the OAM packet leaves the current administrative domain.
5. IANA Considerations
There are no IANA actions required by this draft.
6. Acknowledgements
The editors gratefully acknowledge the contributions of Matthew
Bocci, Italo Busi, Thomas Dietz, Huub van Helvoort, Wataru Imajuku,
Marc Lasserre, Lieven Levrau, Han Li, Julien Meuric, Philippe Niger,
Benjamin Niven-Jenkins, Jing Ruiquan, Nurit Sprecher, Yuji Tochio,
Satoshi Ueno and Yaacov Weingarten.
The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the
MPLS-TP Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS-TP.
7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] ITU-T Recommendation G.806, "Characteristics of transport
equipment - Description methodology and generic functionality",
2009.
[3] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
[4] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
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Pseudowires", RFC 5085, December 2007.
7.2. Informative References
[5] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in
Transport Networks", draft-ietf-mpls-tp-framework-00 (work in
progress), November 2008.
[6] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and
S. Ueno, "MPLS-TP Requirements",
draft-ietf-mpls-tp-requirements-09 (work in progress),
June 2009.
[7] ITU-T Supplement Y.Sup4, "ITU-T Y.1300-series: Supplement on
transport requirements for T-MPLS OAM and considerations for
the application of IETF MPLS technology", 2008.
[8] Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
Matsushima, "Operations and Management (OAM) Requirements for
Multi-Protocol Label Switched (MPLS) Networks", RFC 4377,
February 2006.
[9] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "BFD
For MPLS LSPs", draft-ietf-bfd-mpls-07 (work in progress),
June 2008.
[10] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-05
(work in progress), June 2009.
Authors' Addresses
Martin Vigoureux (editor)
Alcatel-Lucent
Route de Villejust
Nozay, 91620
France
Email: martin.vigoureux@alcatel-lucent.com
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David Ward (editor)
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
Email: dward@cisco.com
Malcolm Betts (editor)
Huawei
Email: malcolm.betts@huawei.com
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