Internet DRAFT - draft-ietf-mpls-tp-oam-analysis
draft-ietf-mpls-tp-oam-analysis
Network Working Group N. Sprecher
Internet-Draft Nokia Siemens Networks
Intended status: Informational L. Fang
Expires: October 18, 2012 Cisco
April 17, 2012
An Overview of the OAM Tool Set for MPLS based Transport Networks
draft-ietf-mpls-tp-oam-analysis-09.txt
Abstract
This document provides an overview of the OAM toolset for MPLS based
Transport Networks (MPLS-TP). The toolset consists of a comprehensive
set of fault management and performance monitoring capabilities
(operating in the data-plane) which are appropriate for transport
networks as required in RFC 5860 and support the network and services
at different nested levels. This overview includes a brief recap of
MPLS-TP OAM requirements and functions, and of generic mechanisms
created in the MPLS data plane to allow the OAM packets run in-band
and share their fate with data packets. The protocol definitions for
each of the MPLS-TP OAM tools are defined in separate documents (RFCs
or Working Group drafts) which are referenced by this document.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 18, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Contributing Authors . . . . . . . . . . . . . . . . . . . 5
1.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Basic OAM Infrastructure Functionality . . . . . . . . . . . . 6
3. MPLS-TP OAM Functions . . . . . . . . . . . . . . . . . . . . 8
3.1. Continuity Check and Connectivity Verification . . . . . . 8
3.1.1. Documents for CC-CV tools . . . . . . . . . . . . . . 9
3.2. Remote Defect Indication . . . . . . . . . . . . . . . . . 9
3.2.1. Documents for RDI . . . . . . . . . . . . . . . . . . 9
3.3. Route Tracing . . . . . . . . . . . . . . . . . . . . . . 9
3.3.1. Documents for Route Tracing . . . . . . . . . . . . . 10
3.4. Alarm Reporting . . . . . . . . . . . . . . . . . . . . . 10
3.4.1. Documents for Alarm Reporting . . . . . . . . . . . . 10
3.5. Lock Instruct . . . . . . . . . . . . . . . . . . . . . . 10
3.5.1. Documents for Lock Instruct . . . . . . . . . . . . . 10
3.6. Lock Reporting . . . . . . . . . . . . . . . . . . . . . . 10
3.6.1. Documents for Lock Reporting . . . . . . . . . . . . . 10
3.7. Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . 11
3.7.1. Documents for Diagnostic Testing . . . . . . . . . . . 11
3.8. Packet Loss Measurement . . . . . . . . . . . . . . . . . 11
3.8.1. Documents for Packet Loss Measurement . . . . . . . . 11
3.9. Packet Delay Measurement . . . . . . . . . . . . . . . . . 12
3.9.1. Documents for Delay Measurement . . . . . . . . . . . 12
4. MPLS-TP OAM documents guide . . . . . . . . . . . . . . . . . 12
5. OAM Toolset Applicability and Utilization . . . . . . . . . . 14
5.1. Connectivity Check and Connectivity Verification . . . . . 14
5.2. Diagnostic Tests and Lock Instruct . . . . . . . . . . . . 15
5.3. Lock Reporting . . . . . . . . . . . . . . . . . . . . . . 16
5.4. Alarm Reporting and Link Down Indication . . . . . . . . . 16
5.5. Remote Defect Indication . . . . . . . . . . . . . . . . . 17
5.6. Packet Loss and Delay Measurement . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
1.1. Scope
The MPLS Transport Profile (MPLS-TP) architectural framework is
defined in [RFC 5921], and it describes common set of protocol
functions that supports the operational models and capabilities
typical of such networks.
OAM (Operations, Administration, and Maintenance) plays a significant
role in carrier networks, providing methods for fault management and
performance monitoring in both the transport and the service layers
in order to improve their ability to support services with guaranteed
and strict Service Level Agreements (SLAs) while reducing their
operational costs.
[RFC 5654], in general, and [RFC 5860], in particular, define a set
of requirements for OAM functionality for MPLS-Transport Profile
(MPLS-TP)Label Switched Paths (LSPs) ), Pseudowires (PWs) and
sections.
The OAM solution, developed by the joint IETF and ITU-T MPLS-TP
project, has three objectives:
o The OAM toolset should be developed based on existing MPLS
architecture, technology, and toolsets.
o The OAM operational experience should be similar to that in other
transport networks.
o The OAM toolset developed for MPLS based transport networks needs
to be fully inter-operable with existing MPLS OAM tools as
documented in [RFC 5860].
The MPLS-TP OAM toolset is based on the following existing tools:
o LSP-Ping as defined in [RFC 4379].
o Bidirectional Forwarding Detection (BFD) as defined in [RFC 5880]
and refined in [RFC 5884].
o ITU-T OAM for Ethernet toolset as defined in [Y.1731]. This has
been used for functionality guidelines for the performance
measurement tools that were not previously supported in MPLS.
It should be noted that certain extensions and adjustments have been
specified relative to the existing MPLS tools, in order to conform to
the transport environment and the requirements of MPLS-TP. However,
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compatibility with the existing tools has been maintained.
This document provides an overview of the MPLS-TP OAM toolset, which
consists of tools for MPLS-TP fault management and performance
monitoring. This overview includes a brief recap of MPLS-TP OAM
requirements and functions, and of the generic mechanisms used to
support the MPLS-TP OAM operation.
The protocol definitions for each individual MPLS-TP OAM tool are
specified in separate RFCs (or Working Group documents while this
document is work in progress), which are referenced by this document.
In addition, the document includes a table that cross-references the
solution documents to the OAM functionality supported. Finally, the
document presents the applicability and utilization of each tool in
the MPLS-TP OAM toolset.
1.2. Contributing Authors
Elisa Bellagamba Ericsson
Yaacov Weingarten Nokia Siemens Networks
Dan Frost Cisco
Nabil Bitar Verizon
Raymond Zhang Alcatel Lucent
Lei Wang Telenor
Kam Lee Yap XO Communications
John Drake Juniper
Yaakov Stein RAD
Anamaria Fulignoli Ericsson
Italo Busi Alcatel Lucent
Huub van Helvoort Huawei
Thomas Nadeau Computer Associate
Henry Yu TW Telecom
Mach Chen Huawei
Manuel Paul Deutsche Telekom
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1.3. Acronyms
This document uses the following acronyms:
ACH Associated Channel Header
AIS Alarm Indication Signal
BFD Bidirectional Forwarding Detection
CC-CV Continuity Check and Connectivity Verification
DM Delay Measurement
FM Fault Management
G-ACh Generic Associated Channel
GAL G-ACh Label
GMPLS Generalized Multi-Protocol Label Switching
IANA Internet Assigned Names Authority
LDI Link Down Indication
LKR Lock Report
LM Loss Measurement
LOC Loss of Continuity
LSP Label Switched Path
MEP Maintenance Entity Group End Point
MEG Maintenance Entity Group
MIP Maintenance Entity Group Intermediate Point
MPLS MultiProtocol Label Switching
MPLS-TP Transport Profile for MPLS
OAM Operations, Administration, and Maintenance
PM Performance Monitoring
PW Pseudowire
RDI Remote Defect Indication
SLA Service Level Agreement
TLV Type, Length, Value
VCCV Virtual Circuit Connectivity Verification
2. Basic OAM Infrastructure Functionality
[RFC 5860] defines a set of requirements on OAM architecture and
general principles of operations, which are evaluated below:
[RFC 5860] requires that --
o OAM mechanisms in MPLS-TP are independent of the transmission
media and of the client service being emulated by the PW ([RFC
5860], section 2.1.2).
o MPLS-TP OAM must be able to support both an IP based and non-IP
based environment. If the network is IP based, i.e. IP routing
and forwarding are available, then it must be possible to choose
to make use of IP capabilities. On the other hand, in
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environments where IP functionality is not available, the OAM
tools must still be able to operate independent of IP forwarding
and routing ([RFC 5860], section 2.1.4). It is required to have
OAM interoperability between distinct domains materializing the
environments ([RFC 5860], section 2.1.5).
o all OAM protocols support identification information, at least in
the form of IP addressing structure and be extensible to support
additional identification schemes ([RFC 5860], section 2.1.4).
o OAM packets and the user traffic are congruent (i.e. OAM packets
are transmitted in-band) and there is a need to differentiate OAM
packets from user-plane packets ([RFC 5860], section 2.1.3).
Inherent in this requirement is the principle that full operation
of the MPLS-TP OAM must be possible independently of the control
or management plane used to operate the network ([RFC 5860],
section 2.1.3).
o MPLS-TP OAM supports point-to-point bidirectional PWs, point-to-
point co-routed bidirectional LSPs, point-to-point bidirectional
Sections ([RFC 5860], section 2.1.1). The applicability of
particular MPLS-TP OAM functions to point-to-point associated
bidirectional LSPs, point-to-point unidirectional LSPs, and point-
to-multipoint LSPs, is described in ([RFC 5860], section 2.2)).
In addition, MPLS-TP OAM supports these LSPs and PWs when they
span either a single or multiple domains ([RFC 5860], section
2.1.1).
o OAM packets may be directed to an intermediate point of a LSP/PW
([RFC 5860], sections 2.2.3, 2.2.4 and 2.2.5).
[RFC 5860] recommends that any protocol solution, meeting one or more
functional requirement(s), be the same for PWs, LSPs, and Sections
(section 2.2).
The following document-set addresses the basic requirements listed
above:
o The [RFC 6371] document describes the architectural framework for
conformance to the basic requirements listed above. It also
defines the basic relationships between the MPLS structures, e.g.
LSP, PW, and the structures necessary for OAM functionality, i.e.
the Managed Entity Group, its End-points, and Intermediate Points.
o The [RFC 5586] document specifies the use of the MPLS-TP in-band
control channels. It generalizes the applicability of the
Pseudowire (PW) Associated Channel Header (ACH) to MPLS LSPs and
Sections, by defining a Generic Associated Channel (G-ACh). The
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G-ACh allows control packets to be multiplexed transparently over
LSPs and sections, similar to that of PW VCCV [RFC 5085]. The
Generic Association Label (GAL) is defined by assigning a reserved
MPLS label value and is used to identify the OAM control packets.
The value of the ACH Channel Type field indicates the specific
protocol carried on the associated control channel. Each MPLS-TP
OAM protocol has an IANA assigned channel type allocated to it.
[RFC 5085] defines an Associated Channel Header (ACH) which
provides a PW associated control channel between a PW's endpoints,
over which OAM and other control messages can be exchanged. [RFC
5586] generalizes MPLS-TP generalized the PW Associated Channel
Header (ACH) to provide common in-band control channels also at
the LSP and MPLS-TP link levels. The G-ACh allows control packets
to be multiplexed transparently over the same LSP or MPLS-TP link
as in PW VCCV. Multiple control channels can exist between end
points.
[RFC 5085] also defines a label-based exception mechanism that
helps an LSR to identify the control packets and direct them to
the appropriate entity for processing. The use of G-ACh and GAL
provides the necessary mechanisms to allow OAM packets run in-band
and share their fate with data packets. It is expected that all
of the OAM protocols will be used in conjunction with this Generic
Associated Channel.
o The [RFC 6370] document provides an IP-based identifier set for
MPLS-TP that can be used to identify the transport entities in the
network and referenced by the different OAM protocols.
[MPLS TP ITU Idents] augments that set of identifiers to include
identifier information in a format used by the ITU-T. Other
identifier sets may be defined as well.
3. MPLS-TP OAM Functions
The following sections discuss the OAM functions that are required in
[RFC 5860] and expanded upon in [RFC 6371].
3.1. Continuity Check and Connectivity Verification
Continuity Check and Connectivity Verification (CC-CV) are OAM
operations generally used in tandem, and complement each other.
These functions are generally run proactively, but may also be used
on-demand for diagnoses of a specific condition. Proactively [RFC
5860] states that the function should allow the MEPs to monitor the
liveliness and connectivity of a transport path (LSP, PW or a
section) between them. In on-demand mode, this function should
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support monitoring between the MEPs and, in addition, between a MEP
and MIP. Note that as specified in sections 3.3 and 3.4 of [RFC
6371], a MEP and a MIP can reside in an unspecified location within a
node, or in a particular interface on a specific side of the
forwarding engine.
The [RFC 6371] highlights the need for the CC-CV messages to include
unique identification of the MEG that is being monitored and the MEP
that originated the message. The function, both proactively and in
on-demand mode, needs to be transmitted at regular transmission rates
pre-configured by the operator.
3.1.1. Documents for CC-CV tools
[RFC 6428] defines BFD extensions to support proactive CC-CV
applications.
[RFC 6426] provides LSP-Ping extensions that are used to implement
on-demand Connectivity Verification.
Both of these tools will be used within the framework of the basic
tools described above, in section 2.
3.2. Remote Defect Indication
Remote Defect Indication (RDI) is used by a path end-point to report
that a defect is detected on a bi-directional connection to its peer
end-point. [RFC 5860] points out that this function may be applied
to a unidirectional LSP only if a return path exists. [RFC 6371]
points out that this function is associated with the proactive CC-CV
function.
3.2.1. Documents for RDI
The [RFC 6428] document includes an extension for BFD that would
include the RDI indication in the BFD format, and a specification of
how this indication is to be used.
3.3. Route Tracing
[RFC 5860] defines that there is a need for functionality that would
allow a path end-point to identify the intermediate (if any) and end-
points of the path (LSP, PW or a section). This function would be
used in on-demand mode. Normally, this path will be used for
bidirectional PW, LSP, and sections, however, unidirectional paths
may be supported only if a return path exists.
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3.3.1. Documents for Route Tracing
The [RFC 6426] document that specifies the LSP-Ping enhancements for
MPLS-TP on-demand Connectivity Verification includes information on
the use of LSP-Ping for route tracing of a MPLS-TP transport path.
3.4. Alarm Reporting
Alarm Reporting is a function used by an intermediate point of a path
(LSP or PW), that becomes aware of a fault on the path, to report to
the end-points of the path. [RFC 6371] states that this may occur as
a result of a defect condition discovered at a server layer. The
intermediate point generates an Alarm Indication Signal (AIS) that
continues until the fault is cleared. The consequent action of this
function is detailed in [RFC 6371].
3.4.1. Documents for Alarm Reporting
MPLS-TP defines a new protocol to address this functionality that is
documented in [RFC 6427]. This protocol uses all of the basic
mechanisms detailed in Section 2.
3.5. Lock Instruct
The Lock Instruct function is an administrative control tool that
allows a path end-point to instruct its peer end-point to lock the
path (LSP, PW or section). The tool is necessary to support single-
side provisioning for administrative locking, according to [RFC
6371]. This function is used on-demand.
3.5.1. Documents for Lock Instruct
The [RFC 6435] document describes the details of a new ACH based
protocol format for this functionality.
3.6. Lock Reporting
Lock reporting, defined in [RFC 5860], is similar to the Alarm
Reporting function described above. It is used by an intermediate
point to notify the end points of a transport path (LSP or PW) that
an administrative lock condition exists for this transport path.
3.6.1. Documents for Lock Reporting
MPLS-TP defines a new protocol to address this functionality that is
documented in [RFC 6427]. This protocol uses all of the basic
mechanisms detailed in Section 2.
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3.7. Diagnostic
The [RFC 5860] indicates that there is need to provide a OAM function
that would enable conducting different diagnostic tests on a PW, LSP,
or Section. The [RFC 6371] provides two types of specific tests to
be used through this functionality:
o Throughput Estimation - allowing the provider to verify the
bandwidth/throughput of a transport path. This is an out-of-
service tool, that uses special packets of varying sizes to test
the actual bandwidth and/or throughput of the path.
o Data-plane loopback - this out-of-service tool causes all traffic
that reaches the target node, either a MEP or MIP, to be looped
back to the originating MEP. For targeting MIPs, a co-routed bi-
directional path is required.
3.7.1. Documents for Diagnostic Testing
The [RFC 6435] document describes the details of a new ACH based
protocol format for the Data-plane loopback functionality.
The tool for Throughput Estimation tool is under study.
3.8. Packet Loss Measurement
Packet Loss Measurement is required by [RFC 5860] to provide a
quantification of the packet loss ratio on a transport path. This is
the ratio of the number of user packets lost to the total number of
user packets during a defined time interval. To employ this
function, [RFC 6371] defines that the two end-points of the transport
path should exchange counters of messages transmitted and received
within a time period bounded by loss-measurement messages. The
framework warns that there may be small errors in the computation
that result from various issues.
3.8.1. Documents for Packet Loss Measurement
The [RFC 6374] document describes the protocol formats and procedures
for using the tool and enable efficient and accurate measurement of
packet loss, delay, and throughput in MPLS networks. [RFC 6375]
describes a profile of the general MPLS loss, delay, and throughput
measurement techniques that suffices to meet the specific
requirements of MPLS-TP. Note that the tool logic is based on the
behavior of the parallel function described in [Y.1731].
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3.9. Packet Delay Measurement
Packet Delay Measurement is a function that is used to measure one-
way or two-way delay of a packet transmission between a pair of the
end-points of a path (PW, LSP, or Section), as described in [RFC
5860]. Where:
o One-way packet delay is the time elapsed from the start of
transmission of the first bit of the packet by a source node until
the reception of the last bit of that packet by the destination
node.
o Two-way packet delay is the time elapsed from the start of
transmission of the first bit of the packet by a source node until
the reception of the last bit of the loop-backed packet by the
same source node, when the loopback is performed at the packet's
destination node.
[RFC 6371] describes how the tool could be performed (both in
proactive and on-demand modes) for either one-way or two-way
measurement. However, it warns that the one-way delay option
requires precise time synchronization between the end-points.
3.9.1. Documents for Delay Measurement
The [RFC 6374] document describes the protocol formats and procedures
for using the tool and enable efficient and accurate measurement of
packet loss, delay, and throughput in MPLS networks. [RFC 6375]
describes a profile of the general MPLS loss, delay, and throughput
measurement techniques that suffices to meet the specific
requirements of MPLS-TP. Note that the tool logic is based on the
behavior of the parallel function described in [Y.1731].
4. MPLS-TP OAM documents guide
The complete MPLS-TP OAM protocol suite is covered by a small set of
existing IETF documents. This set of documents may be expanded in
the future to cover additional OAM functionality. In order to allow
the reader to understand this set of documents, a cross-reference of
the existing documents (IETF RFCs or Internet drafts while this
document is work in progress) for the initial phase of the
specification of MPLS based transport networks is provided below.
[RFC 5586] provides a specification of the basic structure of
protocol messages for in-band data plane OAM in an MPLS environment.
[RFC 6370] provides definitions of different formats that may be used
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within OAM protocol messages to identify the network elements of a
MPLS based transport network.
The following table (Table 1) provides the summary of proactive
MPLS-TP OAM Fault Management toolset functions, associated tool/
protocol, and the corresponding IETF RFCs where they are defined.
+--------------------------+-------------------------------+--------+
| OAM Functions | OAM Tools/Protocols | RFCs |
+--------------------------+-------------------------------+--------+
| Continuity Check and | Bidirectional Forwarding | [RFC |
| Connectivity | Detection (BFD) | 6428] |
| Verification | | |
+--------------------------+-------------------------------+--------+
| Remote Defect Indication | Flag in Bidirectional | [RFC |
| (RDI) | Forwarding Detection (BFD) | 6428] |
| | message | |
+--------------------------+-------------------------------+--------+
| Alarm Indication Signal | G-ACh bases AIS message | [RFC |
| (AIS) | | 6427] |
+--------------------------+-------------------------------+--------+
| Link Down Indication | Flag in AIS message | [RFC |
| (LDI) | | 6427] |
+--------------------------+-------------------------------+--------+
| Lock Reporting (LKR) | G-ACh bases LKR message | [RFC |
| | | 6427] |
+--------------------------+-------------------------------+--------+
Proactive Fault Management OAM Toolset
Table 1
The following table (Table 2) provides an overview of the on-demand
MPLS-TP OAM Fault Management toolset functions, associated tool/
protocol, and the corresponding IETF RFCs they are defined.
+------------------------+---------------------------------+--------+
| OAM Functions | OAM Tools/Protocols | RFCs |
+------------------------+---------------------------------+--------+
| Connectivity | LSP Ping | [RFC |
| Verification | | 6426] |
+------------------------+---------------------------------+--------+
| Diagnostic: Loopback | (1) G-ACh based Loopback and | [RFC |
| and Lock Instruct | Lock Instruct, (2) LSP Ping | 6435] |
+------------------------+---------------------------------+--------+
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+------------------------+---------------------------------+--------+
| Lock Instruct(LI) | Flag in AIS message | [RFC |
| | | 6427] |
+------------------------+---------------------------------+--------+
On Demand Fault Management OAM Toolset
Table 2
The following table (Table 3) provides the Performance Monitoring
Fuctions, asscociated tool/protocol definitions, and corresponding
RFCs.
+----------------------+--------------------------+-----------------+
| OAM Functions | OAM Tools/Protocols | RFCs |
+----------------------+--------------------------+-----------------+
| Packet Loss | G-ACh based LM & DM | [RFC 6374] [RFC |
| Measurement (LM) | query messages | 6375] |
+----------------------+--------------------------+-----------------+
| Packet Delay | G-ACh based LM & DM | [RFC 6374] [RFC |
| Measurement (DM) | query messages | 6375] |
+----------------------+--------------------------+-----------------+
| Throughput | derived from Loss | [RFC 6374] [RFC |
| Measurement | Measurement | 6375] |
+----------------------+--------------------------+-----------------+
| Delay Variation | derived from Delay | [RFC 6374] [RFC |
| Measurement | Measurement | 6375] |
+----------------------+--------------------------+-----------------+
Performance Monitoring OAM Toolset
Table 3
5. OAM Toolset Applicability and Utilization
The following subsections present the MPLS-TP OAM toolset from the
perspective of the specified protocols and identifies which of the
required functionality is supported by the particular protocol.
5.1. Connectivity Check and Connectivity Verification
Proactive Continuity Check and Connectivity Verification (CC-CV)
functions are used to detect loss of continuity (LOC), and unintended
connectivity between two MEPs. Loss of connectivity, mis-merging,
mis-connectivity, or unexpected Maintenance Entity Group End Points
(MEPs) can be detected using the CC-CV tools. See Section 3.1, 3.2,
3.3 in this document for CC-CV protocol references.
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The CC-CV tools are used to support MPLS-TP fault management,
performance management, and protection switching. Proactive CC-CV
control packets are sent by the source MEP to sink MEP. The sink MEP
monitors the arrival of the CC-CV control packets and detects the
defect. For bidirectional transport paths, the CC-CV protocol is,
usually, transmitted simultaneously in both directions.
The transmission interval of CC-CV control packet can be configured.
For example:
o 3.3ms is the default interval for protection switching.
o 100ms is the default interval for performance monitoring.
o 1s is the default interval for fault management.
5.2. Diagnostic Tests and Lock Instruct
[RFC 6435] describes a protocol that provides a mechanism is provided
to Lock and unlock traffic (e.g. data and control traffic) or
specific OAM traffic at a specific LSR on the path of the MPLS-TP LSP
to allow loop back of the traffic to the source.
These diagnostic functions apply to associated bidirectional MPLS-TP
LSPs, including MPLS-TP LSPs, bi-directional RSVP-TE tunnels (which
is relevant for MPLS-TP dynamic control plane option with GMPLS), and
single segment and multi-segment pseudowires. [RFC 6435] provides
the protocol definition for diagnostic tests functions.
The Lock operation instruction is carried in an MPLS Loopback request
message sent from a MEP to a trail-end MEP of the LSP to request that
the LSP be taken out of service. In response, the Lock operation
reply is carried in a Loopback response message sent from the trail-
end MEP back to the originating MEP to report the result.
The loopback operations include:
o Lock: take an LSP out of service for maintenance.
o Unlock: Restore a previously locked LSP to service.
o Set_Full_Loopback and Set_OAM_Loopback
o Unset_Full_Loopback and Set_OAM_Loopback
Operators can use the loopback mode to test the connectivity or
performance (loss, delay, delay variation, and throughput) of given
LSP up to a specific node on the path of the LSP.
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5.3. Lock Reporting
The Lock Report (LKR) function is used to communicate to the client
(sub-) layer MEPs the administrative locking of a server (sub-) layer
MEP, and consequential interruption of data traffic forwarding in the
client (sub-) layer. See Section 3.6 in this document for Lock
Reporting protocol references.
When operator is taking the LSP out of service for maintenance or
other operational reason, using the LKR function can help to
distinguish the condition as administrative locking from defect
condition.
The Lock Report function would also serve the purpose of alarm
suppression in the MPLS-TP network above the level at which the Lock
has occurred. The receipt of an LKR message may be treated as the
equivalent of loss of continuity at the client layer.
5.4. Alarm Reporting and Link Down Indication
Alarm Indication Signal (AIS) message serves the purpose of alarm
suppression upon the failure detection in the server (-sub) layer.
When the Link Down Indication (RDI) is set, the AIS message may be
used to trigger recovery mechanisms.
When a server MEP detects the failure, it asserts Loss of Continuity
(LOC) or signal fail which sets the flag up to generate OAM packet
with AIS message. The AIS message is forwarded to downstream sink
MEP in the client layer. This would enable the client layer to
suppress the generation of secondary alarms.
A Link Down Indication (LDI) flag is defined in the AIS message. The
LDI flag is set in the AIS message in response to detecting a fatal
failure in the server layer. Receipt of an AIS message with this
flag set may be interpreted by a MEP as an indication of signal fail
at the client layer.
The protocols for Alarm Indication Signal (AIS) and Link Down
Indication (LDI) are defined in [RFC 6427].
Fault OAM messages are generated by intermediate nodes where an LSP
is switched, and propagated to the end points (MEPs).
From a practical point of view, when both proactive Continuity Check
functions and LDI are used, one may consider running the proactive
Continuity Check functions at a slower rate (e.g. longer BFD hello
intervals), and reply on LDI to trigger fast protection switch over
upon failure detection in a given LSP.
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5.5. Remote Defect Indication
Remote Defect Indication (RDI) function enables an End Point to
report to the other End Point that a fault or defect condition is
detected on the PW, LSP, or Section for which they are the End
Points.
The RDI OAM function is supported by the use of Bidirectional
Forwarding Detection (BFD) Control Packets [RFC 6428]. RDI is only
used for bidirectional connections and is associated with proactive
CC-CV activation.
When an end point (MEP) detects a signal failure condition, it sets
the flag up by setting the diagnostic field of the BFD control packet
to a particular value to indicate the failure condition on the
associated PW, LSP, or Section, and transmitting the BFD control
packet with the failure flag up to the other end point (its peer
MEP).
The RDI function can be used to facilitate protection switching by
synchronizing the two end points when unidirectional failure occurs
and is detected by one end.
5.6. Packet Loss and Delay Measurement
The packet loss and delay measurement toolset enables operators to
measure the quality of the packet transmission over a PW, LSP, or
Section. Section 3.8 in this document defined the protocols for
packet loss measurement and 3.9 in defined the protocols for packet
delay measurement.
The loss and delay protocols have the following characteristics and
capabilities:
o They support measurement of packet loss, delay and throughput over
Label Switched Paths (LSPs), pseudowires, and MPLS sections.
o The same LM and DM protocols can be used for both continuous/
proactive and selective/on-demand measurement.
o The LM and DM protocols use a simple query/response model for
bidirectional measurement that allows a single node - the querier
- to measure the loss or delay in both directions.
o The LM and DM protocols use query messages for unidirectional loss
and delay measurement. The measurement can either be carried out
at the downstream node(s) or at the querier if an out-of-band
return path is available.
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o The LM and DM protocols do not require that the transmit and
receive interfaces be the same when performing bidirectional
measurement.
o The LM supports test-message-based measurement (i.e. inferred
mode) as well as measurement based on data-plane counters (i.e.
direct mode).
o The LM protocol supports both 32-bit and 64-bit counters.
o The LM protocol supports measurement in terms of both packet
counts and octet counts although for simplicity only packet
counters are currently included in the MPLS-TP profile.
o The LM protocol can be used to measure channel throughput as well
as packet loss.
o The DM protocol supports varying the measurement message size in
order to measure delays associated with different packet sizes.
o The DM protocol uses IEEE 1588 timestamps by default but also
supports other timestamp formats such as NTP.
6. IANA Considerations
This document makes no request of IANA.
The OAM tools and functions defined under G-ACh use IANA assigned
code points. the codes are defined in the corresponding IETF RFCs
Note to RFC Editor:
this section may be removed on publication as an RFC.
7. Security Considerations
This document as an overview of MPLS OAM tools does not by itself
raise any particular security considerations.
The general security considerations are provided in [RFC 6920] and
[MPLS-TP Security Frwk]. Security considerations for each function
in the OAM toolset have been documented in each document that
specifies the particular functionality.
OAM in general is always an area where the security risk is high,
e.g. confidential information may be intercepted for attackers to
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again access to the networks, therefore authentication,
authorization, and encryption need to be enforced for prevent
security breach.
In addition to implement security protocol, tools, and mechanisms,
following strict operation security procedures is very important,
especially MPSL-TP static provisioning processes involve operator
direct interactions with NMS and devices, its critical to prevent
human errors and malicious attacks.
Since MPLS-TP OAM uses G-ACh, the security risks and mitigation
described in [RFC 5085] apply here. In short, the G-ACh could be
intercepted, or false G-ACh packets could be inserted. DoS attack
could happen by flooding G-ACh messages to peer devices. To mitigate
this type of attacks, throttling mechanisms can be used. For more
details, please see [RFC 5085].
8. Acknowledgements
The authors would like to thank the MPLS-TP experts from both the
IETF and ITU-T for their helpful comments. In particular, we would
like to thank Loa Andersson, and the Area Directors for their
suggestions and enhancements to the text.
Thanks to Tom Petch for useful comments and discussions.
Thanks to Rui Costa for his review and comments which helped improve
this doecument.
9. References
9.1. Normative References
[RFC 4379]
Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC 5085]
Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
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[RFC 5586]
Bocci, M., Bryant, S., and M. Vigoureux, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC 5654]
Niven-Jenkins, B., Nadeau, T., and C. Pignataro,
"Requirements for the Transport Profile of MPLS",
RFC 5654, April 2009.
[RFC 5860]
Vigoureux, M., Betts, M., and D. Ward, "Requirements for
OAM in MPLS Transport Networks", RFC 5860, April 2009.
[RFC 5880]
Katz, D. and D. Ward, "Bidirectional Forwarding
Detection", RFC 5880, February 2009.
[RFC 5884]
Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"BFD For MPLS LSPs", RFC 5884, June 2008.
[RFC 5921]
Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
Berger, "A Framework for MPLS in Transport Networks",
RFC 5921, July 2010.
[RFC 6370]
Bocci, M., Swallow, G., and E. Gray, "MPLS-TP
Identifiers", RFC 6370, September 2011.
[RFC 6371]
Busi, I., Niven-Jenkins, B., and D. Allan, "MPLS-TP OAM
Framework and Overview", RFC 6371, September 2011.
[RFC 6374]
Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
[RFC 6375]
Frost, D. and S. Bryant, "A Packet Loss and Delay
Measurement Profile for MPLS-based Transport Networks",
RFC 6375, September 2011.
[RFC 6426]
Bahadur, N., Aggarwal, R., Boutros, S., and E. Gray, "MPLS
on-demand Connectivity Verification, Route Tracing and
Adjacency Verification", RFC 6426, August 2011.
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[RFC 6427]
Swallow, G., Fulignoli, A., and M. Vigoureux, "MPLS Fault
Management OAM", RFC 6427, September 2011.
[RFC 6428]
Allan, D. and G. Swallow, "Proactive Connectivity
Verification, Continuity Check and Remote Defect
indication for MPLS Transport Profile", RFC 6428,
August 2011.
[RFC 6435]
Boutros, S., Sivabalan, S., Aggarwal, R., Vigoureux, M.,
and X. Dai, "MPLS Transport Profile Lock Instruct and
Loopback Functions", RFC 6435, September 2011.
9.2. Informative References
[MPLS-TP Security Frwk]
Fang, L., Niven-Jenkins, B., and S. Mansfield, "MPLS-TP
Security Framework",
ID draft-ietf-mpls-tp-security-framework-02, May 2011.
[RFC 6920]
Fang, L., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[Y.1731] International Telecommunications Union - Standardization,
"OAM functions and mechanisms for Ethernet based
networks", ITU Y.1731, May 2006.
[MPLS TP ITU Idents]
Winter, R., van Helvoort, H., and M. Betts, "MPLS-TP
Identifiers Following ITU-T Conventions",
ID draft-ietf-mpls-tp-itu-t-identifiers-02, July 2011.
Authors' Addresses
Nurit Sprecher
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Email: nurit.sprecher@nsn.com
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Luyuan Fang
Cisco
111 Wood Avenue South
Iselin, NJ 08830
USA
Email: lufang@cisco.com
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