Network Working Group Seisho Yasukawa
Internet Draft NTT Corp
Expires: April 2006
Adrian Farrel
Old Dog Consulting
Daniel King
DNNI Ltd.
Thomas D. Nadeau
Cisco Systems, Inc.
October 2005
OAM Requirements for Point-to-Multipoint MPLS Networks
draft-yasukawa-mpls-p2mp-oam-reqs-01.txt
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Abstract
Multi-Protocol Label Switching (MPLS) has been extended to encompass
point-to-multipoint (P2MP) Label Switched Paths (LSPs). As with
point-to-point MPLS LSPs the requirement to detect, handle and
diagnose control and dataplane defects is critical.
For operators deploying services based on P2MP MPLS LSPs the
detection and specification of how to handle those defects is
important because such defects may not only affect the fundamental
of an MPLS network, but also because they MAY impact service level
specification commitments for customers of their network.
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This document describes requirements for user and data plane
operations and management for P2MP MPLS LSPs. These requirements
apply to all forms of P2MP MPLS LSPs, and include P2MP Traffic
Engineered (TE) LSPs and multicast LSPs.
Table of Contents
1. Introduction .................................................. 2
2. Terminology ................................................... 3
2.1 Conventions ................................................ 3
2.2 Terminology ................................................ 3
2.3 Acronyms ................................................... 3
3. Motivations ................................................... 3
4. General Requirements .......................................... 4
4.1 Detection of Label Switch Path Defects ..................... 4
4.2 Diagnosis of a Broken Label Switch Path .................... 5
4.3 Path characterization ...................................... 5
4.4 Service Level Agreement Measurement ........................ 5
4.5 Frequency of OAM Execution ................................. 6
4.6 Alarm Suppression, Aggregation and Layer Coordination ...... 6
4.7 Support for OAM Interworking for Fault Notification ........ 6
4.8 Error Detection and Recovery ............................... 7
4.9 Standard Management Interfaces ............................. 7
4.10 Detection of Denial of Service Attacks ................... 7
4.11 Per-LSP Accounting Requirements ........................... 8
5. Security Considerations ....................................... 8
6. IANA Considerations ........................................... 8
7. References .................................................... 9
7.1 Normative References ....................................... 9
7.2 Informative References ..................................... 9
8. Acknowledgements ............................................. 10
9. Authors' Addresses ........................................... 10
10. Intellectual Property Statement ............................. 10
11. Full Copyright Statement .................................... 11
1. Introduction
This document describes requirements for user and data plane
operations and management (OAM) for point-to-multipoint (P2MP)
Multi-Protocol Label Switching (MPLS). These requirements have been
gathered from network operators who have extensive experience
deploying MPLS networks and from operators who are considering
deploying P2MP MPLS networks. This draft specifies OAM requirements
for P2MP MPLS, as well as for applications of P2MP MPLS.
These requirements apply to all forms of P2MP MPLS LSPs, and include
P2MP Traffic Engineered (TE) LSPs [P2MP-SIG-REQ] and [P2MP-RSVP], as
well as multicast LDP LSPs [P2MP-LDP] and [MCAST-LDP].
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Note that the requirements for OAM for P2MP MPLS build heavily on the
requirements for OAM for point-to-point MPLS. These latter are
described in [MPLS-OAM] and are not repeated in this document.
2. Terminology
2.1 Conventions used in this document
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].
2.2 Terminology
Definitions of key terms for MPLS OAM are found in [MPLS-OAM] and
the reader is assumed to be familiar with those definitions which
are not repeated here.
[P2MP-SIG-REQ] includes some important definitions and terms for use
within the context of P2MP MPLS. The reader should be familiar with
at least the terminology section of that document.
2.3 Acronyms
The following list of acronyms is a repeat of common acronyms defined
in many other documents, and is provided here for convenience.
CE: Customer Edge
DoS: Denial of service
ECMP: Equal Cost Multipath
LDP: Label Distribution Protocol
LSP: Label Switch Path
LSR: Label Switch Router
OAM: Operations and Management
OA&M: Operations, Administration and Maintenance.
RSVP: Resource reSerVation Protocol
P2MP: Point-to-Multipoint
SP: Service Provider
TE: Traffic Engineering
3. Motivations
OAM for MPLS networks has been established as a fundamental
requirement both through operational experience and through
its documentation in numerous Internet drafts. Many such
documents (for example, [LSP-PING], [RFC3812], [RFC3813], [RFC3814],
and [RFC3815]) developed specific solutions to individual issues or
problems. Coordination of the full OAM requirements for MPLS was
achieved by [MPLS-OAM] in recognition of the fact that the previous
piecemeal approach could lead to inconsistent and inefficient
applicability of OAM techniques across the MPLS architecture, and
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might require significant modifications to operational procedures and
systems in order to provide consistent and useful OAM functionality.
This document builds on these realizations and extends the
statements of MPLS OAM requirements to cover the new area of P2MP
MPLS. That is, this document captures the requirements for P2MP
MPLS OAM in advance of the development of specific solutions.
Nevertheless, at the time of writing, some effort had already
been expended to extend existing MPLS OAM solutions to cover P2MP
MPLS (for example, [P2MP-LSP-PING]). While this approach of extending
existing solutions may be reasonable, in order to ensure a consistent
OAM framework it is necessary to articulate the full set of
requirements in a single document. This will facilitate a uniform set
of MPLS OAM solutions spanning multiple MPLS deployments and
concurrent applications.
4. General Requirements
The general requirements described in this section are closely
similar to those described for point-to-point MPLS in [MPLS-OAM].
The subsections below do not repeat material from [MPLS-OAM], but
simply give references to that document.
However, where the requirements for P2MP MPLS OAM differ from or are
more extensive than those expressed in [MPLS-OAM], additional text is
supplied.
In general, it should be noted that P2MP LSPs introduce a scalability
issue that is not present in point-to-point MPLS. That is, an
individual P2MP LSP will have more than one egress and the path to
those egresses will very probably not be linear (for example, it may
have a tree structure). Since the number of egresses for a single
P2MP LSP is unknown and not bounded by any small number, it follows
that all mechanisms defined for OAM support must scale well with the
number of egresses and the complexity of the path of the LSP.
Mechanisms that are able to deal with individual egresses will scale
no worse than similar mechanisms for point-to-point LSPs, but it is
desirable to develop mechanisms that are able to leverage the fact
that multiple egresses are associated with a single LSP, and so
achieve better scaling.
4.1 Detection of Label Switch Path Defects
The ability to detect defects in a broken Label Switch Path
(LSP) SHOULD not require manual hop-by-hop troubleshooting of
each LSR used to switch traffic for that P2MP LSP. Any
solutions should either extend or work in close conjunction
with existing solutions developed for point-to-point MPLS, such as
those specified in [LSP-PING]. This will leverage existing software
and hardware deployments.
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Note that P2MP LSPs may introduce additional scaling concerns for
LSP probing by tools such as [LSP-PING]. As the number of leaves
of the P2MP LSP increases so it becomes potentially more expensive to
inspect the LSP to detect defects. Any tool developed for this
purpose MUST be cognitive of this issue and MUST include techniques
to reduce the scaling impact of an increase in the number of leaves.
Nevertheless, it should also be noted that the introduciton of
additional leaves may mean that the use of techniques such as
[LSP-PING] are less appropriate for defect detection of P2MP LSPs,
while the technique may still remain useful for defect diagnosis as
described in the next section.
4.2 Diagnosis of a Broken Label Switch Path
The ability to diagnose a broken P2MP LSP and to isolate the failed
component (i.e., link or node) in the path is required. These
functions include a path connectivity test that can test all branches
and leaves of a P2MP LSP for reachability, as well as a path tracing
function. It must be possible for the operator (or an automated
process) to stipulate a timeout after which the failure to see a
response shall be flagged as an error.
Any mechanism developed to perform these functions are subject to the
scalability concerns expressed in section 4.
4.3 Path Characterization
The path characterization function [MPLS-OAM] is the ability to
reveal details of LSR forwarding operations for P2MP LSPs. These
details can then be compared later during subsequent testing relevant
to OAM functionality. Therefore, LSRs supporting P2MP LSPs MUST
provide mechanisms that allow operators to interogate and
characterize P2MP paths.
Since P2MP paths are more complex than the paths of point-to-point
LSPs, the scaling concerns expressed in section 4 apply.
Note that path characterization should lead to the operator being
able to determine the full tree for a P2MP LSP. That is, it is not
sufficient to know the list of LSRs in the tree, but it is important
to know their relative order and where the LSP branches.
Since, in some cases, the control plane state and data paths may
branch at different points from the control plane and data plane
topologies (for example, figure 1), it is not sufficient to present
the order of LSRs, but it is important that the branching points on
that tree are clearly identified.
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E
/
A---B---C===D
\
F
Figure 1. An example P2MP tree where the data path and control plane
state branch at C, but the topology branches at D.
A diagnostic tool that meets the path characterization requirements
SHOULD collect information that is easy to process to determine the
P2MP tree for a P2MP LSP, rather than provide information that must
be post-processed with some complexity.
4.4 Service Level Agreement Measurement
Mechanisms are required to measure the diverse aspects of Service
Level Agreements for services that utlize P2MP LSPs. The aspects are
listed in [MPLS-OAM].
Service Level Agreements are often measured in terms of the quality
and rate of data delivery. In the context of P2MP MPLS, data is
delivered to multiple egress nodes. The mechanisms MUST, therefore,
be capable of measuring the aspects of Service Level Agreements as
they apply to each of the egress points to a P2MP LSP. At the same
time, in order to diagnose issues with meeting Service Level
Agreements, mechanisms SHOULD be provided to measure the aspects of
the agreements at key points within the network such as at branch
nodes on the P2MP tree.
4.5 Frequency of OAM Execution
As stipulated in [MPLS-OAM], the operator MUST have the flexibility
to configure OAM parameters to meet their specific operational
requirements. This requirement is potentially more important in P2MP
deployments where the effects of the execution of OAM functions can
be potentially much greater than in a non-P2MP configuration. For
example, a mechanism that causes each egress of a P2MP LSP to respond
could result in a large burst of responses for a single OAM request.
Therefore, solutions produced SHOULD NOT impose any fixed limitations
on the frequency of the execution of any OAM functions.
4.6 Alarm Suppression, Aggregation and Layer Coordination
As described in [MPLS-OAM], network elements MUST provide alarm
suppression and aggregation to prevent the generation of superfluous
alarms within or across network layers. The same time constraint
issues identified in [MPLS-OAM] also exist for P2MP LSPs.
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A P2MP LSP also brings the possiblity of a single fault causing a
larger number of alarms than for a point-to-point LSP. This can
happen because there are a larger number of downstream LSRs (for
example, a larger number of egresses). The resultant multiplier in
the number of alarms could cause swamping of the alarm management
systems to which the alarms are reported, and serves as a multiplier
to the number of potentially duplicate alarms raised by the network.
Alarm aggregation or limitation techniques MUST be applied within any
solution, or be available within an implementation, so that this
scaling issue can be reduced. Note that this requirement introduces a
second dimension to the concept of alarm aggregation. Where
previously it applied to the correlation and suppression of alarms
generated by different network layers, it now also applies to similar
techniques applied to alarms generated by multiple downstream LSRs.
4.7 Support for OAM Interworking for Fault Notification
[MPLS-OAM] specifies that an LSR supporting the interworking of
one or more networking technologies over MPLS MUST be able to
translate an MPLS defect into the native technology's error
condition. This also applies to any LSR supporting P2MP
LSPs. However, careful attention to the requirements for
alarm suppression stipulated therein and in section 4.6 SHOULD
be observed.
Note that the time constraints for fault notification and alarm
propagation impact upon the solutions that might be applied to the
scalability problem inherent in certain OAM techniques applied to
P2MP LSPs. For example, a solution to the issue of a large number
of egresses all responding to some form of probe request at the
same time, might be to make the probes less frequent - but this
might impact on the ability to detect and/or report faults.
Where fault notification to the egress is required, there is the
possiblity that a single fault will give rise to multiple
notifications, one to each egress node of the P2MP that is downstream
of the fault. Any mechanisms MUST manage this scaling issue while
still continuing to deliver fault notifications in a timely manner.
Where fault notification to the ingress is required, the mechanisms
MUST ensure that the notification identifies the egress nodes of the
P2MP LSP that are impacted (that is, those downstream of the fault)
and does not falsely imply that all egress nodes are impacted.
4.8 Error Detection and Recovery
Recovery from a fault by a network element can be facilitated by
MPLS OAM procedures. As described in [MPLS-OAM], these procedures
will detect a broad range of defects, and SHOULD be operable where
MPLS P2MP LSPs span multiple routing areas, or multiple Service
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Provider domains.
The same requirements as those expressed in [MPLS-OAM] with respect
to automatic repair and operator intervention ahead of customer
detection of faults apply to P2MP LSPs.
It should be observed that faults in P2MP LSPs may be recovered
through techniques described in [P2MP-RSVP].
4.9 Standard Management Interfaces
The wide-spread deployment of MPLS requires common information
modeling of management and control of OAM functionality. This is
reflected in the the integration of standard MPLS-related MIBs
[RFC3813], [RFC3812], [RFC3814], [RFC3815] for fault, statistics
and configuration management. These standard interfaces provide
operators with common programmatic interface access to
operations and management functions and their status. These
The standard MPLS-related MIB modules [RFC3812], [RFC3813],
[RFC3814], and [RFC3815] SHOULD be extended wherever possible, to
support P2MP LSPs, the associated OAM functions on these LSPs, and
the applications that utlize P2MP LSPs. Extending them will
facillitate the reuse of existing management software both in LSRs
and in management systems. In cases where the existing MIB modules
cannot be extended, then new MIB modules MUST be created.
4.10 Detection of Denial of Service Attacks
The ability to detect denial of service (DoS) attacks against the
data or control planes which signal P2MP LSPs MUST be part of
any security management related to MPLS OAM tools or techniques.
4.11 Per-LSP Accounting Requirements
In an MPLS network where P2MP LSPs are in use, Service Providers can
measure traffic from an LSR to the egress of the network using some
MPLS-related MIB modules (see section 4.9), for example. Other
interfaces MAY exist as well and enable the creation of traffic
matricies so that it is possible to know how much traffic is
traveling from where to where within the network.
Analysis of traffic flows to produce a traffic matrix is more
complicated where P2MP LSPs are deployed becasue there is no simple
pairing relationship between an ingress and a single egress.
Fundamental to understanding traffic flows within a network that
supports P2MP LSPs will be the knowledge of where the traffic is
branched for each LSP within the network. That is, where within the
network the branch nodes for the LSPs are located and what their
relationship is to links and other LSRs. The Traffic flow and
accounting tools MUST take this fact into account.
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5. Security Considerations
This document introduces no new security issues compared with
[MPLS-OAM]. It is worth highlighting, however, that any tool designed
to satisfy the requirements described in this document MUST include
provisions to prevent its unauthorized use. Likewise, these tools
MUST provide a means by which an operator can prevent denial of
service attacks if those tools are used in such an attack.
LSP mis-merging is described in [MPLS-OAM] where it is pointed out
that it has security implications beyond simply being a network
defect. It needs to be stressed that it is in the nature of P2MP
traffic flows that any erroneous delivery (such as caused by LSP
mis-merging) is likely to have more far reaching conseuqences since
the traffic will be mis-delivered to multiple receivers.
As with previous OAM function described in [MPLS-OAM], the
performance of diagnostic functions and path characterization may
involve the extraction of a significant amount of information about
network construction. The network operator MAY consider this
information private and wish to take steps to secure it, but further,
the volume of this information may be considered as a threat to the
integrity of the network if it is extacted in bulk. This issue may be
greater in P2MP MPLS becuase of the potential for a large number of
receivers on a single LSP and the consequent extensive path of the
LSP.
6. IANA Considerations
This document creates no new requirements on IANA namespaces.
7. References
7.1 Normative References
[MPLS-OAM] T. Nadeau, Allan D., et al. Allan D.,
"OAM Requirements for MPLS Networks",
draft-ietf-mpls-oam-requirements-05.txt,
December 2004
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2 Informative References
[LSP-PING] Kompella, K., and Swallow, G., (Editors), "Detecting
MPLS Data Plane Failures", draft-ietf-mpls-lsp-ping,
work in progress.
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[MCAST-LDP] Wijnands, IJ., et al., " Multicast Extensions for
LDP", draft-wijnands-mpls-ldp-mcast-ext, work in
progress.
[P2MP-LDP] Minei, I., et al., "Label Distribution Protocol
Extensions for Point-to-Multipoint Label Switched
Paths", draft-minei-mpls-ldp-p2mp, work in progress.
[P2MP-LSP-PING] Yasukawa, S., Farrel, A., Ali, Z., and Fenner, B.,
"Detecting Data Plane Failures in
Point-to-Multipoint MPLS Traffic Engineering -
Extensions to LSP Ping",
draft-yasukawa-mpls-p2mp-lsp-ping, work in progress.
[P2MP-RSVP] Aggarwal, R., Papadimitriou, D., and Yasukawa, S.,
"Extensions to RSVP-TE for Point to Multipoint TE
LSPs", draft-ietf-mpls-rsvp-te-p2mp, work in
progress.
[P2MP-SIG-REQ] Yasukawa, S. (Editor), "Signaling Requirements for
Point to Multipoint Traffic Engineered MPLS LSPs",
draft-ietf-mpls-p2mp-sig-requirement, work in
progress.
[RFC3812] Srinivasan, C., Viswanathan, A. and T.
Nadeau, "MPLS Traffic Engineering Management
Information Base Using SMIv2", RFC3812, June 2004.
[RFC3813] Srinivasan, C., Viswanathan, A. and T.
Nadeau, "MPLS Label Switch Router Management
Information Base Using SMIv2", RFC3813, June 2004.
[RFC3814] Nadeau, T., Srinivasan, C., and A.
Viswanathan, "Multiprotocol Label Switching
(MPLS) FEC-To-NHLFE (FTN) Management
Information Base", RFC3814, June 2004.
[RFC3815] Cucchiara, J., Sjostrand, H., and Luciani, J.,
"Definitions of Managed Objects for the
Multiprotocol Label Switching (MPLS), Label
Distribution Protocol (LDP)", RFC 3815, June 2004.
8. Acknowledgment
The authors wish to acknowledge and thank the following
individuals for their valuable comments to this document:
Dimitri Papadimitriou and Rahul Aggarwal.
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9. Authors' Addresses
Adrian Farrel
Old Dog Consulting
Phone: +44 (0) 1978 860944
Email: adrian@olddog.co.uk
Daniel King
Darwinian Neural Network Industries Ltd.
Phone: +44 (0)1249 665923
Email: dan@dnni.com
Thomas D. Nadeau
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
Email: tnadeau@cisco.com
Seisho Yasukawa
NTT Corporation
9-11, Midori-Cho 3-Chome
Musashino-Shi, Tokyo 180-8585,
Japan
Phone: +81 422 59 4769
Email: yasukawa.seisho@lab.ntt.co.jp
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this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
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11. Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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