Here is Tom Nadeau's feedback, forwarded with permission:
Regards, Benoit
==============
Some general comments:
1. I did not find any discussion around use of configuration within OAM
mechanisms. This is clearly something that is happening in groups
like PWE3 and CCAMP. The motivation for this should be explained and
documented to at least guide these efforts.
2. There is no real discussion around the security aspects of these
tools. Should there be?
3. While the document provides a nice taxonomy of various OAM tools, it
does not really discuss the techniques for using them. I do not expect
anything in detail, but it is not obvious that many of these tools can
be orchestrated to form a "toolset" that can be used to do multi-layer
OAM functions for services such as carrier Ethernet over VPLS over MPLS,
for example.
4. It might be useful to at least mention in the performance metrics
section, a discussion around the accuracy of these tools and how it
depends on scale, implementation and network configurations.
My detailed comments inline starting with TOM:
--Tom
Expires: July 2013 Nokia Siemens Networks
E. Bellagamba
Ericsson
Y. Weingarten
January 9, 2013
An Overview of
Operations, Administration, and Maintenance (OAM) Mechanisms
draft-ietf-opsawg-oam-overview-08.txt
Abstract
Operations, Administration, and Maintenance (OAM) is a general term
that refers to a toolset that can be used for fault detection and
isolation, and for performance measurement. OAM mechanisms have been
defined for various layers in the protocol stack, and are used
with a
variety of protocols.
This document presents an overview of the OAM mechanisms that have
been defined and are currently being defined by the IETF.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance
with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 9, 2013.
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Copyright Notice
Copyright (c) 2013 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ................................................. 3
1.1. The Building Blocks of OAM .............................. 3
1.2. Forwarding Plane vs. Management Plane ................... 4
1.3. The OAM toolsets ........................................ 4
1.4. IETF OAM Documents ...................................... 6
1.5. Non-IETF OAM Documents ................................. 10
2. Basic Terminology ........................................... 12
2.1. Abbreviations .......................................... 12
2.2. Terminology used in OAM Standards ...................... 13
2.2.1. General Terms ..................................... 13
2.2.2. OAM Maintenance Entities .......................... 13
2.2.3. OAM Maintenance Points ............................ 14
2.2.4. Proactive and On-demand activation ................ 15
2.2.5. Connectivity Verification and Continuity Checks ... 15
2.2.6. Failures .......................................... 15
3. OAM Tools ................................................... 16
3.1. IP Ping and Traceroute ................................. 16
3.1.1. Ping .............................................. 16
3.1.2. Traceroute......................................... 16
3.2. Bidirectional Forwarding Detection (BFD) ............... 17
3.2.1. Overview .......................................... 17
3.2.2. BFD Control ....................................... 17
3.2.3. BFD Echo .......................................... 18
3.3. MPLS OAM ............................................... 18
3.4. MPLS-TP OAM ............................................ 19
3.4.1. Overview .......................................... 19
3.4.2. Generic Associated Channel ........................ 19
3.4.3. MPLS-TP OAM Toolset ............................... 20
3.4.3.1. Continuity Check and Connectivity Verification 20
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3.4.3.2. Route Tracing ................................ 21
3.4.3.3. Lock Instruct ................................ 21
3.4.3.4. Lock Reporting ............................... 21
3.4.3.5. Alarm Reporting .............................. 21
3.4.3.6. Remote Defect Indication ..................... 22
3.4.3.7. Client Failure Indication .................... 22
3.4.3.8. Packet Loss Measurement (LM) ................. 22
3.4.3.9. Packet Delay Measurement (DM) ................ 22
3.5. PWE3 OAM ............................................... 23
3.5.1. PWE3 OAM using Virtual Circuit Connectivity
Verification
(VCCV) ................................................... 23
3.5.2. PWE3 OAM using G-ACh .............................. 24
3.6. OWAMP and TWAMP......................................... 24
3.6.1. Overview .......................................... 24
3.6.2. Control and Test Protocols ........................ 24
3.6.3. OWAMP ............................................. 25
3.6.4. TWAMP ............................................. 26
3.7. Summary of OAM Functions ............................... 26
4. Security Considerations ..................................... 27
5. IANA Considerations ......................................... 27
6. Acknowledgments ............................................. 27
7. References .................................................. 28
7.1. Normative References ................................... 28
7.2. Informative References ................................. 31
1. Introduction
OAM is a general term that refers to a toolset for detecting,
isolating and reporting connection failures and performance
degradation.
This document summarizes the OAM tools and mechanisms defined in the
IETF.
The term OAM in this document refers to Operations, Administration
and Maintenance [OAM-Def], focusing on the forwarding plane of OAM.
Hence, management aspects are outside the scope of this document.
TOM: This is a curious sentence to me since to me, OAM is management, or
a subset of it. Also, if you look at the referenced documents, there
are many indirect references to MIBs, Netconf, etc... making this
sentence further confusing. It might be helpful to explain more clearly
that the authors here intended to not cover those things explicitly
rather than grouping them arbitrarily under the definition of
"management aspects" Further, to clarify, it might be useful to expand
on what "forwarding plane" is here just to be clear. That is, is this
"in band" or "out-of band" or both? Some of the tools referred to here
also are part of the control AND data planes.
1.1. The Building Blocks of OAM
An OAM protocol is run in the context of a Maintenance Domain,
consisting of two or more nodes that run the OAM protocol, referred
to as Maintenance Points (MP).
This subsection provides a brief summary of the common tools used by
OAM protocols. An OAM protocol typically supports one or more of the
tools described below.
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o Continuity Checking (CC):
Used for verifying the liveness of a connection between two MPs.
o Connectivity Verification (CV):
Allows an MP to check whether it is connected to a peer MP,
and to
verify that messages from the peer MP are received through the
expected path.
o Path Discovery / Fault Localization:
An MP uses this mechanism to trace the route to a peer MP, i.e.,
to identify the nodes along the path to the peer MP. When a
connection fails, this mechanism also allows the MP to detect the
location of the failure.
TOM: The definition calls this "path discovery" but then talks about
tracing routes. A better way of describing this in the paragraph would
be that there I a use of path tracing in order to discover (or
re-discover) paths that have been changed, created or destroyed.
o Performance Monitoring:
Consists of 3 main functions
o Loss Measurement (LM) - monitors the packet loss rate of a
connection.
o Delay Measurement (DM) - monitors the delay and delay
variation between MPs.
o Throughput measurement - monitors the throughput of a
connection.
TOM: Along with the discussion above around path trace/discovery, it is
imperative that paths be discovered (one way or another) in order to
successfully d performance monitoring on those paths.
1.2. Forwarding Plane vs. Management Plane
While the OAM tools may, and quite often do, work in conjunction
with
a control-plane or management plane, they are usually defined to be
independent of the control-plane. The OAM tools communicate
with the
management plane to raise alarms, and often the on-demand tools may
be activated by the management, e.g. to locate and localize
problems.
The considerations of the control-plane maintenance tools or the
functionality of the management-plane are out of scope for this
document, which will concentrate on presenting the forwarding-plane
tools that are used for OAM.
TOM: What about the data plane? For example, the GACH OAM type is such
an example. VCCV also operates within the data plane after its
configuration capabilities have been signaled. It should also be
mentioned that it is imperative that when required, OAM tools are
capable of testing the actual data plane in as much accuracy as
possible, but that they all should note how accurate. Not all OAM
tools are created equal.
1.3. The OAM toolsets
This memo provides an overview of the different sets of OAM
mechanisms defined by the IETF. It is intended for those with little
or no familiarity with the described mechanisms. The set of OAM
mechanisms described in this memo are applicable to IP unicast,
MPLS,
pseudowires, and MPLS for the transport environment (MPLS-TP). While
OAM mechanisms that are applicable to other technologies exist, they
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are beyond the scope of this memo. This document focuses on IETF
documents that have been published as RFCs, while other ongoing OAM-
related work is outside the scope.
The IETF has defined OAM protocols and mechanisms in several
different fronts:
o IP Ping and Traceroute:
Ping is a very simple and common application for failure
diagnosis
TOM: I am not sure the term "common" is necessary.
that uses ICMP Echo requests, as defined in [ICMPv4], and
[ICMPv6].
Traceroute ([TCPIP-Tools], [NetTools]) is an application that
allows users to trace the path between an IP source and an IP
destination, i.e., to identify the nodes along the path.
o BFD:
Bidirectional Forwarding Detection (BFD) is defined in [BFD] as a
framework for a lightweight generic OAM mechanism. The intention
is to define a base mechanism that can be used with various
encapsulation types, network environments, and in various medium
types.
o MPLS OAM:
MPLS LSP Ping, as defined in [MPLS-OAM], [MPLS-OAM-FW] and [LSP-
Ping], is an OAM mechanism for point to point MPLS LSPs. It
includes two main functions: Ping and Traceroute.
o MPLS-TP OAM:
MPLS-TP OAM is defined in a set of RFCs. The OAM requirements for
MPLS Transport Profile (MPLS-TP) are defined in [MPLS-TP-OAM].
Each of the tools in the OAM toolset is defined in its own
RFC, as
specified in Section 1.4.
o PWE3 OAM:
The PWE3 OAM architecture defines control channels that support
the use of existing IETF OAM tools to be used for a pseudowire
(PW). The control channels that are defined in [VCCV] and [PW-G-
ACH] may be used in conjunction with ICMP Ping, LSP Ping, and BFD
to perform CC and CV functionality. In addition the channels
support use of any of the MPLS-TP based OAM tools for completing
their respective OAM functionality for a PW.
o OWAMP and TWAMP:
The One Way Active Measurement Protocol (OWAMP) and the Two Way
Active Measurement Protocols (TWAMP) are two protocols defined in
the IP Performance Metrics (IPPM) working group in the IETF.
These
protocols allow delay and packet loss measurement in IP networks.
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This document summarizes the OAM mechanisms defined by the IETF. We
first present a comparison of the terminology used in various OAM
standards, and then summarize the OAM functions that each OAM
standard provides.
1.4. IETF OAM Documents
Table 1 summarizes the IETF OAM related RFCs discussed in this
document.
The table includes a "Type" column, specifying the nature of each of
the listed documents:
o Tool: documents that define an OAM tool or mechanism.
o Prof.: documents that define a profile or a variant for an OAM
tool that is defined in other documents.
o Inf.: documents that define an infrastructure that is used by OAM
tools.
o Misc.: other OAM related documents, e.g., OAM requirement and
framework documents.
+-----------+--------------------------------------+-----+----------+
| | Title |Type | RFC |
+-----------+--------------------------------------+-----+----------+
|IP Ping and| Internet Control Message Protocol |Tool | RFC 792 |
|Traceroute | [ICMPv4] | |
|
| +--------------------------------------+-----+----------+
| | Internet Control Message Protocol |Tool | RFC 4443 |
| | (ICMPv6) for the Internet Protocol | |
|
| | Version 6 (IPv6) Specification | |
|
| | [ICMPv6] | |
|
| +--------------------------------------+-----+----------+
| | A Primer On Internet and TCP/IP |Tool | RFC 2151 |
| | Tools and Utilities [TCPIP-Tools] | |
|
| +--------------------------------------+-----+----------+
| | FYI on a Network Management Tool |Tool | RFC 1147 |
| | Catalog: Tools for Monitoring and | |
|
| | Debugging TCP/IP Internets and | |
|
| | Interconnected Devices [NetTools] | |
|
| +--------------------------------------+-----+----------+
| | Extended ICMP to Support Multi-Part |Tool | RFC
4884 |
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| | Messages [ICMP-MP] | |
|
| +--------------------------------------+-----+----------+
| | ICMP Extensions for Multiprotocol |Tool | RFC 4950 |
| | Label Switching [ICMP-Ext] | |
|
| +--------------------------------------+-----+----------+
| | Extending ICMP for Interface and |Tool | RFC 5837 |
| | Next-Hop Identification [ICMP-Int] | |
|
+-----------+--------------------------------------+-----+----------+
|BFD | Bidirectional Forwarding Detection |Tool | RFC 5880 |
| | [BFD] | |
|
| +--------------------------------------+-----+----------+
| | Bidirectional Forwarding Detection |Prof.| RFC 5881 |
| | (BFD) for IPv4 and IPv6 (Single Hop) | |
|
| | [BFD-IP] | |
|
| +--------------------------------------+-----+----------+
| | Generic Application of Bidirectional |Misc.| RFC
5882 |
| | Forwarding Detection [BFD-Gen] | |
|
| +--------------------------------------+-----+----------+
| | Bidirectional Forwarding Detection |Prof.| RFC 5883 |
| | (BFD) for Multihop Paths [BFD-Multi] | |
|
| +--------------------------------------+-----+----------+
| | Bidirectional Forwarding Detection |Prof.| RFC 5884 |
| | for MPLS Label Switched Paths (LSPs) | |
|
| | [BFD-LSP] | |
|
| +--------------------------------------+-----+----------+
| | Bidirectional Forwarding Detection |Prof.| RFC 5885 |
| | for the Pseudowire Virtual Circuit | |
|
| | Connectivity Verification (VCCV) | |
|
| | [BFD-VCCV] | |
|
+-----------+--------------------------------------+-----+----------+
|MPLS OAM | Operations and Management (OAM) |Misc.| RFC 4377 |
| | Requirements for Multi-Protocol Label| |
|
| | Switched (MPLS) Networks [MPLS-OAM] | |
|
| +--------------------------------------+-----+----------+
| | A Framework for Multi-Protocol |Misc.| RFC 4378 |
| | Label Switching (MPLS) Operations | |
|
| | and Management (OAM) [MPLS-OAM-FW] | |
|
| +--------------------------------------+-----+----------+
| | Detecting Multi-Protocol Label |Tool | RFC 4379 |
| | Switched (MPLS) Data Plane Failures | |
|
| | [LSP-Ping] | |
|
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| +--------------------------------------+-----+----------+
| | Operations and Management (OAM) |Misc.| RFC 4687 |
| | Requirements for Point-to-Multipoint | |
|
| | MPLS Networks [MPLS-P2MP] | |
|
+-----------+--------------------------------------+-----+----------+
|MPLS-TP | Requirements for OAM in MPLS-TP |Misc.| RFC 5860 |
|OAM | [MPLS-TP-OAM] | |
|
| +--------------------------------------+-----+----------+
| | MPLS Generic Associated Channel |Inf. | RFC 5586 |
| | [G-ACh] | |
|
| +--------------------------------------+-----+----------+
| | MPLS-TP OAM Framework |Misc.| RFC 6371 |
| | [TP-OAM-FW] | |
|
| +--------------------------------------+-----+----------+
| | Proactive Connectivity Verification, |Tool | RFC
6428 |
| | Continuity Check, and Remote Defect | |
|
| | Indication for the MPLS Transport | |
|
| | Profile [TP-CC-CV] | |
|
| +--------------------------------------+-----+----------+
| | MPLS On-Demand Connectivity |Tool | RFC 6426 |
| | Verification and Route Tracing | |
|
| | [OnDemand-CV] | |
|
| +--------------------------------------+-----+----------+
| | MPLS Fault Management Operations, |Tool | RFC 6427 |
| | Administration, and Maintenance (OAM)| |
|
| | [TP-Fault] | |
|
| +--------------------------------------+-----+----------+
| | MPLS Transport Profile Lock Instruct |Tool | RFC
6435 |
| | and Loopback Functions [Lock-Loop] | |
|
| +--------------------------------------+-----+----------+
| | Packet Loss and Delay Measurement for|Tool | RFC
6374 |
| | MPLS Networks [MPLS-LM-DM] | |
|
| +--------------------------------------+-----+----------+
| | A Packet Loss and Delay Measurement |Prof.| RFC
6375 |
| | Profile for MPLS-Based Transport | |
|
| | Networks [TP-LM-DM] | |
|
+-----------+--------------------------------------+-----+----------+
|PWE3 OAM | Pseudowire Virtual Circuit |Inf. | RFC 5085 |
| | Connectivity Verification (VCCV): | |
|
| | A Control Channel for Pseudowires | |
|
| | [VCCV] | |
|
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| +--------------------------------------+-----+----------+
| | Bidirectional Forwarding Detection |Prof.| RFC 5885 |
| | for the Pseudowire Virtual Circuit | |
|
| | Connectivity Verification (VCCV) | |
|
| | [BFD-VCCV] | |
|
| +--------------------------------------+-----+----------+
| | Using the Generic Associated Channel |Inf. | RFC
6423 |
| | Label for Pseudowire in the MPLS | |
|
| | Transport Profile (MPLS-TP) | |
|
| | [PW-G-ACh] | |
|
| +--------------------------------------+-----+----------+
| | Pseudowire (PW) Operations, |Misc.| RFC 6310 |
| | Administration, and Maintenance (OAM)| |
|
| | Message Mapping [PW-Map] | |
|
+-----------+--------------------------------------+-----+----------+
|OWAMP and | A One-way Active Measurement Protocol|Tool | RFC
4656 |
|TWAMP | [OWAMP] | |
|
| +--------------------------------------+-----+----------+
| | A Two-Way Active Measurement Protocol|Tool | RFC
5357 |
| | [TWAMP] | |
|
| +--------------------------------------+-----+----------+
| | Framework for IP Performance Metrics |Misc.| RFC
2330 |
| | [IPPM-FW] | |
|
| +--------------------------------------+-----+----------+
| | IPPM Metrics for Measuring |Misc.| RFC 2678 |
| | Connectivity [IPPM-Con] | |
|
| +--------------------------------------+-----+----------+
| | A One-way Delay Metric for IPPM |Misc.| RFC 2679 |
| | [IPPM-1DM] | |
|
| +--------------------------------------+-----+----------+
| | A One-way Packet Loss Metric for IPPM|Misc.| RFC
2680 |
| | [IPPM-1LM] | |
|
| +--------------------------------------+-----+----------+
| | A Round-trip Delay Metric for IPPM |Misc.| RFC 2681 |
| | [IPPM-2DM] | |
|
+-----------+--------------------------------------+-----+----------+
Table 1 Summary of IETF OAM Related RFCs
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1.5. Non-IETF OAM Documents
In addition to the OAM mechanisms defined by the IETF, the IEEE and
ITU-T have also defined various OAM mechanisms that focus on
Ethernet, and various other transport network environments. These
various mechanisms, defined by the three standard organizations, are
often tightly coupled, and have had a mutual effect on each other.
The ITU-T and IETF have both defined OAM mechanisms for MPLS LSPs,
[ITU-T-Y1711] and [LSP-Ping]. The following OAM standards by the
IEEE
and ITU-T are to some extent linked to IETF OAM mechanisms listed
above and are mentioned here only as reference material:
o OAM mechanisms for Ethernet based networks have been defined by
both the ITU-T in [ITU-T-Y1731], and by the IEEE in
[IEEE802.1ag].
The IEEE 802.3 standard defines OAM for one-hop Ethernet links
[IEEE802.3ah].
o The ITU-T has defined OAM for MPLS LSPs in [ITU-T-Y1711], and
MPLS-TP OAM in [ITU-G8113.1] and [ITU-G8113.2].
Table 2 summarizes the OAM standards mentioned in this document.
This
document focuses on IETF OAM standards, but these non-IETF standards
are referenced where relevant.
+-----------+--------------------------------------+---------------+
| | Title |Standard/Draft |
+-----------+--------------------------------------+---------------+
|ITU-T | Operation & Maintenance mechanism | ITU-T Y.1711 |
|MPLS OAM | for MPLS networks [ITU-T-Y1711] | |
| +--------------------------------------+---------------+
| | Assignment of the 'OAM Alert Label' | RFC 3429 |
| | for Multiprotocol Label Switching | |
| | Architecture (MPLS) Operation and | |
| | Maintenance (OAM) Functions | |
| | [OAM-Label] | |
| | | |
| | Note: although this is an IETF | |
| | document, it is listed as one of the| |
| | non-IETF OAM standards, since it | |
| | was defined as a complementary part | |
| | of ITU-T Y.1711. | |
+-----------+--------------------------------------+---------------+
|ITU-T | Operations, administration and |ITU-T G.8113.2 |
|MPLS-TP OAM| Maintenance mechanisms for MPLS-TP | |
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| | networks using the tools defined for | |
| | MPLS [ITU-G8113.2] | |
| | | |
| | Note: this document describes the | |
| | OAM toolset defined by the IETF for | |
| | MPLS-TP, whereas ITU-T G.8113.1 | |
| | describes the OAM toolset defined | |
| | by the ITU-T. | |
| +--------------------------------------+---------------+
| | Operations, Administration and |ITU-T G.8113.1 |
| | Maintenance mechanism for MPLS-TP in | |
| | Packet Transport Network (PTN) | |
| +--------------------------------------+---------------+
| | Allocation of a Generic Associated | RFC 6671 |
| | Channel Type for ITU-T MPLS Transport| |
| | Profile Operation, Maintenance, and | |
| | Administration (MPLS-TP OAM) | |
| | [ITU-T-CT] | |
| | | |
| | Note: although this is an IETF | |
| | document, it is listed as one of the| |
| | non-IETF OAM standards, since it | |
| | was defined as a complementary part | |
| | of ITU-T G.8113.1. | |
+-----------+--------------------------------------+---------------+
|ITU-T | OAM Functions and Mechanisms for |[ITU-T-Y1731] |
|Ethernet | Ethernet-based Networks | |
|OAM | | |
+-----------+--------------------------------------+---------------+
|IEEE | Connectivity Fault Management | IEEE 802.1ag |
|CFM | [IEEE802.1ag] | |
| | | |
| | Note: CFM was originally published | |
| | as IEEE 802.1ag, but is now | |
| | incorporated in the 802.1Q standard.| |
+-----------+--------------------------------------+---------------+
|IEEE | Media Access Control Parameters, | IEEE 802.3ah |
|802.3 | Physical Layers, and Management | |
|link level | Parameters for Subscriber Access | |
|OAM | Networks [IEEE802.3ah] | |
| | | |
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| | Note: link level OAM was originally | |
| | defined in IEEE 802.3ah, and is now | |
| | incorporated in the 802.3 standard. | |
+-----------+--------------------------------------+---------------+
Table 2 Non-IETF OAM Standards Mentioned in this Document
2. Basic Terminology
2.1. Abbreviations
ACH Associated Channel Header
AIS Alarm Indication Signal
BFD Bidirectional Forwarding Detection
CC Continuity Check
CV Connectivity Verification
DM Delay Measurement
FEC Forwarding Equivalence Class
GAL Generic Associated Label
ICMP Internet Control Message Protocol
LDP Label Distribution Protocol
LM Loss Measurement
LSP Label Switched Path
ME Maintenance Entity
MEG Maintenance Entity Group
MEP MEG End Point
MIP MEG Intermediate Point
MP Maintenance Point
MPLS Multiprotocol Label Switching
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MPLS-TP MPLS Transport Profile
MTU Maximum Transmission Unit
OAM Operations, Administration, and Maintenance
PW Pseudowire
PWE3 Pseudowire Emulation Edge-to-Edge
RDI Remote Defect Indication
TTL Time To Live
VCCV Virtual Circuit Connectivity Verification
TOM: Why is this section not at the top of this document, as is
customary for RFCs?
2.2. Terminology used in OAM Standards
2.2.1. General Terms
A wide variety of terms is used in various OAM standards. Each
of the
OAM standards listed in the reference section includes a section
that
defines terms relevant to that tool. A thesaurus of terminology for
MPLS-TP terms is presented in [TP-Term], and provides a good summary
of some of the OAM related terminology.
This section presents a comparison of the terms used in various OAM
standards, without fully quoting the definition of each term. For a
formal definition of each term, refer to the references at the
end of
this document.
2.2.2. OAM Maintenance Entities
OAM tools are designed to monitor and manage a Maintenance Entity
(ME). An ME, as defined in [TP-OAM-FW], defines a relationship
between two points of a transport path to which maintenance and
monitoring operations apply.
The following related terms are also quoted from [TP-OAM-FW]:
o MEP: The two points that define a maintenance entity.
o MEG: The collection of one or more MEs that belongs to the same
transport path and that are maintained and monitored as a group
are known as a Maintenance Entity Group (MEG).
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o MIP: In between MEPs, there are zero or more intermediate points,
called Maintenance Entity Group Intermediate Points (MIPs).
A pair of MEPs engaged in an ME are connected by a communication
link, which may be one of several types of connection, e.g. a single
physical connection, a set of physical connections, or a virtual
link
such as an MPLS LSP.
The term Maintenance Entity (ME) is used in ITU-T Recommendations
(e.g. [ITU-T-Y1731]), as well as in the MPLS-TP terminology
([TP-OAM-
FW]). Various terms are used to refer to an ME. For example, BFD
does
not explicitly use a term that is equivalent to ME, but rather uses
the term "session", referring to the relationship between two nodes
using a BFD protocol. The MPLS LSP Ping ([LSP-Ping]) terminology
simply uses the term "LSP" in this context.
MPLS-TP has defined the terms ME and Maintenance Entity Group (MEG)
in [TP-OAM-FW], similar to the terms defined by ITU-T. A MEG allows
the monitoring of a compound set of MEs, for example when monitoring
a p2mp MEG that is considered to be the set of MEs between the root
and each individual destination MEP.
2.2.3. OAM Maintenance Points
A Maintenance Point (MP) is a functional entity that is defined at a
node in the network, and either initiates or reacts to OAM messages.
A Maintenance End Point (MEP) is one of the end points of an ME, and
can initiate OAM messages and respond to them. A Maintenance
Intermediate Point (MIP) is an intermediate point between two MEPs,
that does not generally initiate OAM frames (one exception to
this is
the use of AIS notifications), but is able to respond to OAM frames
that are destined to it. A MIP in MPLS-TP identifies OAM packets
destined to it by the value of the TTL field in the OAM packet. The
term Maintenance Point is a general term for MEPs and MIPs.
The 802.1ag defines a finer distinction between Up MPs and Down MPs.
An MP is a bridge interface, that is monitored by an OAM protocol
either in the direction facing the network, or in the direction
facing the bridge. A Down MP is an MP that receives OAM packets
from,
and transmits them to the direction of the network. An Up MP
receives
OAM packets from, and transmits them to the direction of the
bridging
entity.
MPLS-TP ([TP-OAM-FW]) uses a similar distinction on the placement of
the MP - either at the ingress, egress, or forwarding function
of the
node (Down / Up MPs). This placement is important for localization
of a connection failure.
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2.2.4. Proactive and On-demand activation
The different OAM tools may be used in one of two basic types of
activation:
o Proactive activation - indicates that the tool is activated on a
continual basis periodically, where messages are sent between the
two MEPs, and errors are detected when a certain number of
expected messages are not received.
o On-demand activation - indicates that the tool is activated
"manually" to detect a specific anomaly. In this activation a
small number of OAM messages are sent by a MEP and the reply
message is received.
2.2.5. Connectivity Verification and Continuity Checks
Two distinct classes of failure management functions are used in OAM
protocols, connectivity verification and continuity checks. The
distinction between these terms is defined in [MPLS-TP-OAM], and is
used similarly in this document.
Continuity checks are used to verify the liveness of a connection or
a path between two MPs, and are typically sent proactively, though
they can be invoked on-demand as well.
A connectivity verification function allows an MP to check
whether it
is connected to a peer MP or not. This function also allows the
MP to
verify that messages from the peer MP are received through the
correct path, thereby verifying not only that the two MPs are
connected, but also that they are connected through the expected
path. This allows detection of unexpected topology changes. A
connectivity verification (CV) protocol typically uses a CV message,
followed by a CV reply that is sent back to the originator. A CV
function can be applied proactively or on-demand.
Connectivity verification and continuity checks are considered
complementary mechanisms, and are often used in conjunction with
each
other.
2.2.6. Failures
The terms Failure, Fault, and Defect are used interchangeably in the
standards, referring to a malfunction that can be detected by a
connectivity or a continuity check. In some standards, such as
[IEEE802.1ag], there is no distinction between these terms, while in
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other standards each of these terms refers to a different type of
malfunction.
The terminology used in IETF MPLS-TP OAM takes after the ITU-T,
which
distinguishes between these terms in [ITU-T-G.806]; The term Fault
refers to an inability to perform a required action, e.g., an
unsuccessful attempt to deliver a packet. The term Defect refers to
an interruption in the normal operation, such as a consecutive
period
of time where no packets are delivered successfully. The term
Failure
refers to the termination of the required function. While a Defect
typically refers to a limited period of time, a failure refers to a
long period of time.
3. OAM Tools
3.1. IP Ping and Traceroute
3.1.1. Ping
Ping is a common network diagnosis application for IP networks that
uses ICMP. The ICMP Echo request/reply exchange is a connectivity
verification function for the Internet Protocol. The originator
transmits an ICMP Echo request packet, and the receiver replies with
an Echo reply. ICMP ping is defined in two variants, [ICMPv4] is
used
for IPv4, and [ICMPv6] is used for IPv6.
3.1.2. Traceroute
Traceroute ([TCPIP-Tools], [NetTools]) is an application that allows
users to discover the path between an IP source and an IP
destination. Traceroute sends a sequence of UDP packets to UDP port
33434 at the destination. By default, Traceroute begins by sending
three packets (the number of packets is configurable in most
Traceroute implementations), each with an IP Time-To-Live (TTL)
value
of one to the destination. These packets expire as soon as they
reach
the first router in the path. That router responds by sending three
ICMP Time Exceeded Messages to the Traceroute application.
Traceroute
now sends another three UDP packets, each with the TTL value of 2.
These messages cause the second router to return ICMP messages. This
process continues, with ever increasing values for the TTL field,
until the packets actually reach the destination. Because no
application listens to port 33434 at the destination, the
destination
returns ICMP Destination Unreachable Messages indicating an
unreachable port. This event indicates to the Traceroute application
that it is finished. The Traceroute program displays the round-trip
delay associated with each of the attempts.
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Note that IP routing may be asymmetric. While Traceroute reveals the
path between a source and destination, it may not reveal the reverse
path.
A few ICMP extensions ([ICMP-Ext], [ICMP-MP], [ICMP-Int]) have been
defined in the context of Traceroute. These extensions augment the
ICMP Destination Unreachable message, and can be used by Traceroute
applications.
3.2. Bidirectional Forwarding Detection (BFD)
3.2.1. Overview
While multiple OAM mechanisms have been defined for various
protocols
in the protocol stack, Bidirectional Forwarding Detection [BFD],
defined by the IETF BFD working group, is a generic OAM mechanism
that can be deployed over various encapsulating protocols, and in
various medium types. The IETF has defined variants of the protocol
for IP ([BFD-IP], [BFD-Multi]), for MPLS LSPs [BFD-LSP], and for
PWE3
[BFD-VCCV]. The usage of BFD in MPLS-TP is defined in [MPLS-TP-CC-
CV].
BFD includes two main OAM functions, using two types of BFD packets:
BFD Control packets, and BFD Echo packets.
3.2.2. BFD Control
BFD supports a bidirectional continuity check, using BFD control
packets, that are exchanged within a BFD session. BFD sessions
operate in one of two modes:
o Asynchronous mode (i.e. proactive): in this mode BFD control
packets are sent periodically. When the receiver detects that no
BFD control packet have been received during a predetermined
period of time, a failure is detected.
o Demand mode: in this mode, BFD control packets are sent on-demand.
Upon need, a system initiates a series of BFD control packets to
verify the liveness of the session. BFD control packets are sent
independently in each direction.
Each of the end-points of the monitored path maintains its own
session identification, called a Discriminator, both of which are
included in the BFD Control Packets that are exchanged between the
end-points. At the time of session establishment, the
Discriminators
are exchanged between the two-end points. In addition, the
transmission (and reception) rate is negotiated between the two end-
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points, based on information included in the control packets. These
transmission rates may be renegotiated during the session.
During normal operation of the session, i.e. no failures are
detected, the BFD session is in the Up state. If no BFD Control
packets are received during a fixed period of time, called the
TOM: Fixed, pre-configured or negotiated period of time (i.e.: BFD interval)
Detection Time, the session is declared to be Down. The detection
time is a function of the negotiated transmission time, and a
parameter called Detect Mult. Detect Mult determines the number of
missing BFD Control packets that cause the session to be declared as
Down. This parameter is included in the BFD Control packet.
3.2.3. BFD Echo
A BFD echo packet is sent to a peer system, and is looped back
to the
originator. The echo function can be used proactively, or on-demand.
The BFD echo function has been defined in BFD for IPv4 and IPv6
([BFD-IP]), but is not used in BFD for MPLS LSPs, PWs, or in BFD for
MPLS-TP.
3.3. MPLS OAM
The IETF MPLS working group has defined OAM for MPLS LSPs. The
requirements and framework of this effort are defined in [MPLS-OAM-
FW] and [MPLS-OAM], respectively. The corresponding OAM mechanism
defined, in this context, is LSP Ping [LSP-Ping].
LSP Ping is based on ICMP Ping and just like its predecessor may be
used in one of two modes:
o "Ping" mode: In this mode LSP ping is used for end-to-end
connectivity verification between two LERs.
o "Traceroute" mode: This mode is used for hop-by-hop fault
isolation.
LSP Ping extends the basic ICMP Ping operation (of data-plane
connectivity verification) with functionality to verify data-plane
vs. control-plane consistency for a Forwarding Equivalence Class
(FEC) and also Maximum Transmission Unit (MTU) problems. The
traceroute functionality may be used to isolate and localize the
MPLS
faults, using the Time-to-live (TTL) indicator to incrementally
identify the sub-path of the LSP that is successfully traversed
before the faulty link or node.
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It should be noted that LSP Ping supports unique identification of
the LSP within an addressing domain. The identification is checked
using the full FEC identification. LSP Ping is easily extensible to
include additional information needed to support new functionality,
by use of Type-Length-Value (TLV) constructs. The usage of TLVs is
typically not easy to perform in hardware, and is thus typically
handled by the control plane.
LSP Ping supports both asynchronous, as well as, on-demand
activation.
3.4. MPLS-TP OAM
3.4.1. Overview
The MPLS working group is currently working on defining the OAM
toolset that fulfills the requirements for MPLS-TP OAM. The full set
of requirements for MPLS-TP OAM are defined in [MPLS-TP-OAM], and
include both general requirements for the behavior of the OAM
mechanisms and a set of operations that should be supported by the
OAM toolset. The set of mechanisms required are further elaborated
in [TP-OAM-FW], which describes the general architecture of the OAM
system as well as giving overviews of the functionality of the OAM
toolset.
Some of the basic requirements for the OAM toolset for MPLS-TP are:
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 the MPLS-TP OAM toolset should
rely
on the IP routing and forwarding capabilities. On the other hand,
in environments where IP functionality is not available, the OAM
tools must still be able to operate without dependence on IP
forwarding and routing.
o OAM packets and the user traffic are required to be congruent
(i.e. OAM packets are transmitted in-band) and there is a need to
differentiate OAM packets from user-plane ones. Inherent in this
requirement is the principle that MPLS-TP OAM be independent of
any existing control-plane, although it should not preclude
use of
the control-plane functionality.
3.4.2. Generic Associated Channel
In order to address the requirement for in-band transmission of
MPLS-
TP OAM traffic, MPLS-TP uses a Generic Associated Channel (G-ACh),
defined in [G-ACh] for LSP-based OAM traffic. This mechanism is
based
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on the same concepts as the PWE3 ACH and VCCV mechanisms. However,
to address the needs of LSPs as differentiated from PW, the
following
concepts were defined for [G-ACh]:
o An Associated Channel Header (ACH), that uses a format similar to
the PW Control Word, is a 4-byte header that is prepended to OAM
packets.
o A Generic Associated Label (GAL). The GAL is a reserved MPLS label
value (13) that indicates that the packet is an ACH packet
and the
payload follows immediately after the label stack.
3.4.3. MPLS-TP OAM Toolset
To address the functionality that is required of the OAM
toolset, the
MPLS WG conducted an analysis of the existing IETF and ITU-T OAM
mechanisms and their ability to fulfill the required functionality.
The conclusions of this analysis are documented in [OAM-Analys]. The
MPLS working group currently plans to use a mixture of OAM
mechanisms
that are based on various existing standards, and adapt them to the
requirements of [MPLS-TP-OAM]. Some of the main building blocks of
this solution are based on:
o Bidirectional Forwarding Detection ([BFD], [BFD-LSP]) for
proactive continuity check and connectivity verification.
o LSP Ping as defined in [LSP-Ping] for on-demand connectivity
verification.
o New protocol packets, using G-ACH, to address different
functionality.
o Performance measurement protocols that are based on the
functionality that is described in [ITU-T-Y1731].
The following sub-sections describe the OAM tools defined for
MPLS-TP
as described in [TP-OAM-FW].
3.4.3.1. Continuity Check and Connectivity Verification
Continuity Check and Connectivity Verification are presented in
Section 2.2.5. of this document. As presented there, these
tools may
be used either proactively or on-demand. When using these tools
proactively, they are generally used in tandem.
For MPLS-TP there are two distinct tools, the proactive tool is
defined in [TP-CC-CV] while the on-demand tool is defined in
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[OnDemand-CV].Proactively [MPLS-TP-OAM] states that the function
should allow the MEPs to monitor the liveness and connectivity of a
transport path. In on-demand mode, this function should support
monitoring between the MEPs and, in addition, between a MEP and MIP.
[TP-OAM-FW] highlights, when performing Connectivity Verification,
the need for the CC-V messages to include unique identification of
the MEG that is being monitored and the MEP that originated the
message.
The proactive tool [TP-CC-CV] is based on extensions to BFD (see
Section 3.2. ) with the additional limitation that the transmission
and receiving rates are based on configuration by the operator. The
on-demand tool [OnDemand-CV] is an adaptation of LSP Ping (see
Section 3.3. ) for the required behavior of MPLS-TP.
3.4.3.2. Route Tracing
[MPLS-TP-OAM] defines that there is a need for functionality that
would allow a path end-point to identify the intermediate and end-
points of the path. 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. The tool for this is based on the LSP Ping (see
Section 3.3. ) functionality and is described in [OnDemand-CV].
3.4.3.3. Lock Instruct
The Lock Instruct function [Lock-Loop] is used to notify a transport
path end-point of an administrative need to disable the transport
path. This functionality will generally be used in conjunction with
some intrusive OAM function, e.g. Performance measurement,
Diagnostic
testing, to minimize the side-effect on user data traffic.
3.4.3.4. Lock Reporting
Lock Reporting is a function used by an end-point of a path to
report
to its far-end end-point that a lock condition has been affected on
the path.
3.4.3.5. Alarm Reporting
Alarm Reporting is a function used by an intermediate point of a
path, that becomes aware of a fault on the path, to report to the
end-points of the path. [TP-OAM-FW] states that this may occur as a
result of a defect condition discovered at a server sub-layer. This
generates an Alarm Indication Signal (AIS) that continues until the
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fault is cleared. The consequent action of this function is detailed
in [TP-OAM-FW].
3.4.3.6. Remote Defect Indication
Remote Defect Indication (RDI) is used proactively by a path end-
point to report to its peer end-point that a defect is detected on a
bidirectional connection between them. [MPLS-TP-OAM] points out that
this function may be applied to a unidirectional LSP only if there a
return path exists. [TP-OAM-FW] points out that this function is
associated with the proactive CC-V function.
3.4.3.7. Client Failure Indication
Client Failure Indication (CFI) is defined in [MPLS-TP-OAM] to allow
the propagation information from one edge of the network to the
other. The information concerns a defect to a client, in the case
that the client does not support alarm notification.
3.4.3.8. Packet Loss Measurement (LM)
Packet Loss Measurement is a function used to verify the quality of
the service. This function indicates the ratio of packets that are
not delivered out of all packets that are transmitted by the path
source.
There are two possible ways of determining this measurement:
o Using OAM packets, it is possible to compute the statistics based
on a series of OAM packets. This, however, has the
disadvantage of
being artificial, and may not be representative since part of the
packet loss may be dependent upon packet sizes.
TOM: Not just packet sizes. Things like implementation (as I mentioned
above with the comment about the accuracy or truthfulness of the data
plane processing of OAM packets). Doing very accurate RTT as a simple
example, with just IP Pings, is a tricky thing to make work. Also, it
is important to mention that the scale in terms of number of packets,
number of tests, etc... can and will impact these parameters too.
o Sending delimiting messages for the start and end of a measurement
period during which the source and sink of the path count the
packets transmitted and received. After the end delimiter, the
ratio would be calculated by the path OAM entity.
3.4.3.9. Packet Delay Measurement (DM)
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). Where:
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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.
Similarly to the packet loss measurement this could be performed in
either of the two ways outlined above.
3.5. PWE3 OAM
3.5.1. PWE3 OAM using Virtual Circuit Connectivity Verification (VCCV)
VCCV, as defined in [VCCV], provides a means for end-to-end fault
detection and diagnostics tools to be extended for PWs
(regardless of
the underlying tunneling technology). The VCCV switching function
provides a control channel associated with each PW (based on the PW
Associated Channel Header (ACH) which is defined in [PW-ACH]), and
allows transmitting the OAM packets in-band with PW data (using CC
Type 1: In-band VCCV).
VCCV currently supports the following OAM mechanisms: ICMP Ping, LSP
Ping, and BFD. ICMP and LSP Ping are IP encapsulated before being
sent over the PW ACH. BFD for VCCV [BFD-VCCV] supports two modes of
encapsulation - either IP/UDP encapsulated (with IP/UDP header) or
PW-ACH encapsulated (with no IP/UDP header) and provides support to
signal the AC status. The use of the VCCV control channel provides
the context, based on the MPLS-PW label, required to bind and
bootstrap the BFD session to a particular pseudo wire (FEC),
eliminating the need to exchange Discriminator values.
VCCV consists of two components: (1) signaled component to
communicate VCCV capabilities as part of VC label, and (2) switching
component to cause the PW payload to be treated as a control packet.
VCCV is not directly dependent upon the presence of a control plane.
The VCCV capability negotiation may be performed as part of the PW
signaling when LDP is used. In case of manual configuration of the
PW, it is the responsibility of the operator to set consistent
options at both ends.
TOM: Might be helpful to note that the static mode was created
specifically to handle the MPLS-TP cases where no control plane was a
requirement. However, new use cases such as pure mobile backhaul, etc...
find this functionality useful too.
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3.5.2. PWE3 OAM using G-ACh
As mentioned above, VCCV enables OAM for PWs by using a control
channel for OAM packets. When PWs are used in MPLS-TP networks,
rather than the control channels defined in VCCV, the G-ACh can be
used as an alternative control channel. The usage of the G-ACh for
PWs is defined in [PW-G-ACh].
3.6. OWAMP and TWAMP
3.6.1. Overview
The IPPM working group in the IETF defines common criteria and
metrics for measuring performance of IP traffic ([IPPM-FW]). Some of
the key RFCs published by this working group have defined
metrics for
measuring connectivity [IPPM-Con], delay ([IPPM-1DM], [IPPM-2DM]),
and packet loss [IPPM-1LM].
Alternative protocols for performance measurement are defined, for
example, in MPLS-TP OAM ([MPLS-LM-DM], [TP-LM-DM]), and in Ethernet
OAM [ITU-T-Y1731].
The IPPM working group has defined not only metrics for performance
measurement, but also protocols that define how the measurement is
carried out. The One-way Active Measurement Protocol [OWAMP] and the
Two-Way Active Measurement Protocol [TWAMP] define a method and
protocol for measuring delay and packet loss in IP networks.
OWAMP [OWAMP] enables measurement of one-way characteristics of IP
networks, such as one-way packet loss and one-way delay. For its
proper operation OWAMP requires accurate time of day setting at its
end points.
TWAMP [TWAMP] is a similar protocol that enables measurement of two-
way (round trip) characteristics. TWAMP does not require accurate
time of day, and, furthermore, allows the use of a simple session
reflector, making it an attractive alternative to OWAMP.
OWAMP and TWAMP use two separate protocols: a Control plane
protocol,
and a Test plane protocol.
3.6.2. Control and Test Protocols
OWAMP and TWAMP control protocols run over TCP, while the test
protocols run over UDP. The purpose of the control protocols is to
initiate, start, and stop test sessions, and for OWAMP to fetch
results. The test protocols introduce test packets (which contain
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sequence numbers and timestamps) along the IP path under test
according to a schedule, and record statistics of packet arrival.
Multiple sessions may be simultaneously defined, each with a session
identifier, and defining the number of packets to be sent, the
amount
of padding to be added (and thus the packet size), the start time,
and the send schedule (which can be either a constant time between
test packets or exponentially distributed pseudo-random). Statistics
recorded conform to the relevant IPPM RFCs.
OWAMP and TWAMP test traffic is designed with security in mind.
Test
packets are hard to detect because they are simply UDP streams
between negotiated port numbers, with potentially nothing static in
the packets. OWAMP and TWAMP also include optional authentication
and encryption for both control and test packets.
3.6.3. OWAMP
OWAMP defines the following logical roles: Session-Sender, Session-
Receiver, Server, Control-Client, and Fetch-Client. The Session-
Sender originates test traffic that is received by the Session-
Receiver. The Server configures and manages the session, as well as
returning the results. The Control-Client initiates requests for
test sessions, triggers their start, and may trigger their
termination. The Fetch-Client requests the results of a completed
session. Multiple roles may be combined in a single host - for
example, one host may play the roles of Control-Client,
Fetch-Client,
and Session-Sender, and a second playing the roles of Server and
Session-Receiver.
In a typical OWAMP session the Control-Client establishes a TCP
connection to port 861 of the Server, which responds with a server
greeting message indicating supported security/integrity modes. The
Control-Client responds with the chosen communications mode and the
Server accepts the modes. The Control-Client then requests and
fully
describes a test session to which the Server responds with its
acceptance and supporting information. More than one test session
may be requested with additional messages. The Control-Client then
starts a test session and the Server acknowledges. The Session-
Sender then sends test packets with pseudorandom padding to the
Session-Receiver until the session is complete or until the Control-
client stops the session. Once finished, the Fetch-Client sends a
fetch request to the server, which responds with an acknowledgement
and immediately thereafter the result data.
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3.6.4. TWAMP
TWAMP defines the following logical roles: session-sender, session-
reflector, server, and control-client. These are similar to the
OWAMP roles, except that the Session-Reflector does not collect any
packet information, and there is no need for a Fetch-Client.
In a typical TWAMP session the Control-Client establishes a TCP
connection to port 862 of the Server, and mode is negotiated as in
OWAMP. The Control-Client then requests sessions and starts them.
The Session-Sender sends test packets with pseudorandom padding to
the Session-Reflector which returns them with insertion of
timestamps.
3.7. Summary of OAM Functions
Table 3 summarizes the OAM functions that are supported in each of
the categories that were analyzed in this section.
+-----------+-------+--------+--------+-----------+-------+--------+
| Standard |Continu|Connecti|Path |Defect |Perform|Other |
| |ity |vity |Discover|Indications|ance |Function|
| |Check |Verifica|y | |Monitor|s |
| | |tion | | |ing | |
+-----------+-------+--------+--------+-----------+-------+--------+
|IP Ping | |Echo | | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|IP | | |Tracerou| | | |
|Traceroute | | |te | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|BFD |BFD |BFD | | | | |
| |Control|Echo | | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|MPLS OAM | |"Ping" |"Tracero| | | |
|(LSP Ping) | |mode |ute" | | | |
| | | |mode | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|MPLS-TP |CC |CV/pro- |Route |-Alarm |-LM |-Diagnos|
|OAM | |active |Tracing | Reporting |-DM | tic Tes|
| | |or on- | |-Client | | t |
| | |demand | | Failure | |-Lock |
| | | | | Indication| | |
| | | | |-Remote | | |
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| | | | | Defect | | |
| | | | | Indication| | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|PWE3 OAM |BFD |-BFD |LSP-Ping| | | |
| | |-ICMP | | | | |
| | | Ping | | | | |
| | |-LSP- | | | | |
| | | Ping | | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|OWAMP and | | | | |-Delay | |
|TWAMP | | | | | measur| |
| | | | | | ement | |
| | | | | |-Packet| |
| | | | | | loss | |
| | | | | | measur| |
| | | | | | ement | |
+-----------+-------+--------+--------+-----------+-------+--------+
Table 3 Summary of OAM Functions
4. Security Considerations
This memo presents an overview of existing OAM mechanisms, and
proposes no new OAM mechanisms. Therefore, this document introduces
no security considerations. However, the OAM mechanism reviewed in
this document can and do present security issues. The reader is
encouraged to review the Security Considerations section of each
document reference by this memo.
5. IANA Considerations
There are no new IANA considerations implied by this document.
6. Acknowledgments
The authors gratefully acknowledge Sasha Vainshtein, Carlos
Pignataro, David Harrington, Dan Romascanu, Ron Bonica and other
members of the OPSAWG mailing list for their helpful comments.
This document was prepared using 2-Word-v2.0.template.dot.
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7. References
7.1. Normative References
[LSP-Ping] Kompella, K., Swallow, G., "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[MPLS-OAM] Nadeau, T., Morrow, M., Swallow, G., Allan, D.,
Matsushima, S., "Operations and Management (OAM)
Requirements for Multi-Protocol Label Switched (MPLS)
Networks", RFC 4377, February 2006.
[MPLS-OAM-FW] Allan, D., Nadeau, T., "A Framework for Multi-Protocol
Label Switching (MPLS) Operations and Management
(OAM)", RFC 4378, February 2006.
[OAM-Label] Ohta, H., "Assignment of the 'OAM Alert Label' for
Multiprotocol Label Switching Architecture (MPLS)
Operation and Maintenance (OAM) Functions", RFC 3429,
November 2002.
[MPLS-TP-OAM] Vigoureux, M., Ward, D., Betts, M., "Requirements for
OAM in MPLS Transport Networks", RFC 5860, May 2010.
[G-ACh] Bocci, M., Vigoureux, M., Bryant, S., "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[VCCV] Nadeau, T., Pignataro, C., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel
for Pseudowires", RFC 5085, December 2007.
[PW-ACH] Bryant, S., Swallow, G., Martini, L., McPherson, D.,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word
for Use over an MPLS PSN", RFC 4385, February 2006.
[ICMPv4] Postel, J., "Internet Control Message Protocol",
STD 5,
RFC 792, September 1981.
[ICMPv6] Conta, A., Deering, S., and M. Gupta, "Internet
Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[MPLS-P2MP] Yasukawa, S., Farrel, A., King, D., Nadeau, T.,
"Operations and Management (OAM) Requirements for
Point-to-Multipoint MPLS Networks", RFC 4687,
September 2006.
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[ICMP-Ext] Bonica, R., Gan, D., Tappan, D., Pignataro, C., "ICMP
Extensions for Multiprotocol Label Switching", RFC
4950, August 2007.
[ICMP-MP] Bonica, R., Gan, D., Tappan, D., Pignataro, C.,
"Extended ICMP to Support Multi-Part Messages", RFC
4884, April 2007.
[ICMP-Int] Atlas, A., Bonica, R., Pignataro, C., Shen, N.,
Rivers,
JR., "Extending ICMP for Interface and Next-Hop
Identification", RFC 5837, April 2010.
[TCPIP-Tools] Kessler, G., Shepard, S., "A Primer On Internet and
TCP/IP Tools and Utilities", RFC 2151, June 1997.
[NetTools] Stine, R., "FYI on a Network Management Tool Catalog:
Tools for Monitoring and Debugging TCP/IP Internets
and Interconnected Devices", RFC 1147, April 1990.
[IPPM-FW] Paxson, V., Almes, G., Mahdavi, J., and Mathis, M.,
"Framework for IP Performance Metrics", RFC 2330, May
1998.
[IPPM-Con] Mahdavi, J., Paxson, V., "IPPM Metrics for Measuring
Connectivity", RFC 2678, September 1999.
[IPPM-1DM] Almes, G., Kalidindi, S., Zekauskas, M., "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[IPPM-1LM] Almes, G., Kalidindi, S., Zekauskas, M., "A One-way
Packet Loss Metric for IPPM", RFC 2680, September
1999.
[IPPM-2DM] Almes, G., Kalidindi, S., Zekauskas, M., "A Round-trip
Delay Metric for IPPM", RFC 2681, September 1999.
[OWAMP] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and
Zekauskas, M., "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[TWAMP] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and
Babiarz, J., "A Two-Way Active Measurement Protocol
(TWAMP)", RFC 5357, October 2008.
[BFD] Katz, D., Ward, D., "Bidirectional Forwarding
Detection
(BFD)", RFC 5880, June 2010.
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[BFD-IP] Katz, D., Ward, D., "Bidirectional Forwarding
Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
2010.
[BFD-Gen] Katz, D., Ward, D., "Generic Application of
Bidirectional Forwarding Detection (BFD)", RFC 5882,
June 2010.
[BFD-Multi] Katz, D., Ward, D., "Bidirectional Forwarding
Detection
(BFD) for Multihop Paths", RFC 5883, June 2010.
[BFD-LSP] Aggarwal, R., Kompella, K., Nadeau, T., and Swallow,
G., "Bidirectional Forwarding Detection (BFD) for MPLS
Label Switched Paths (LSPs)", RFC 5884, June 2010.
[BFD-VCCV] Nadeau, T., Pignataro, C., "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", RFC 5885, June
2010.
[TP-OAM-FW] Busi, I., Allan, D., "Operations, Administration and
Maintenance Framework for MPLS-based Transport
Networks ", RFC 6371, September 2011.
[TP-CC-CV] Allan, D., Swallow, G., Drake, J., "Proactive
Connectivity Verification, Continuity Check and Remote
Defect indication for MPLS Transport Profile", RFC
6428, November 2011.
[OnDemand-CV] Gray, E., Bahadur, N., Boutros, S., Aggarwal, R. "MPLS
On-Demand Connectivity Verification and Route
Tracing", RFC 6426, November 2011.
[MPLS-LM-DM] Frost, D., Bryant, S., "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September
2011.
[TP-LM-DM] Frost, D., Bryant, S., "A Packet Loss and Delay
Measurement Profile for MPLS-Based Transport
Networks", RFC 6375, September 2011.
[TP-Fault] Swallow, G., Fulignoli, A., Vigoureux, M.,
Boutros, S.,
"MPLS Fault Management Operations, Administration, and
Maintenance (OAM)", RFC 6427, November 2011.
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[Lock-Loop] Boutros, S., Sivabalan, S., Aggarwal, R., Vigoureux,
M., Dai, X., "MPLS Transport Profile Lock Instruct and
Loopback Functions", RFC 6435, November 2011.
[ITU-T-CT] Betts, M., "Allocation of a Generic Associated Channel
Type for ITU-T MPLS Transport Profile Operation,
Maintenance, and Administration (MPLS-TP OAM)", RFC
6671, November 2012.
[PW-Map] M. Aissaoui, P. Busschbach, L. Martini, M. Morrow, T.
Nadeau, "Pseudowire (PW) Operations, Administration,
and Maintenance (OAM) Message Mapping", RFC 6310, July
2011.
[PW-G-ACh] Li, H., Martini, L., He, J., Huang, F., "Using the
Generic Associated Channel Label for Pseudowire in the
MPLS Transport Profile (MPLS-TP)", RFC 6423, November
2011.
7.2. Informative References
[OAM-Def] Andersson, L., Van Helvoort, H., Bonica, R.,
Romascanu,
D., Mansfield, S., "Guidelines for the use of the OAM
acronym in the IETF ", RFC 6291, June 2011.
[OAM-Analys] Sprecher, N., Fang, L., "An Overview of the OAM Tool
Set for MPLS based Transport Networks", RFC 6669,
July 2012.
[TP-Term] Van Helvoort, H., Andersson, L., Sprecher, N., "A
Thesaurus for the Terminology used in Multiprotocol
Label Switching Transport Profile (MPLS-TP)
drafts/RFCs and ITU-T's Transport Network
Recommendations", work-in-progress, draft-ietf-mpls-
tp-rosetta-stone, July 2012.
[IEEE802.1ag] IEEE 802.1Q, "IEEE Standard for Local and metropolitan
area networks - Media Access Control (MAC) Bridges and
Virtual Bridged Local Area Networks", October 2012.
[ITU-T-Y1731] ITU-T Recommendation G.8013/Y.1731, "OAM Functions and
Mechanisms for Ethernet-based Networks", July 2011.
[ITU-T-Y1711] ITU-T Recommendation Y.1711, "Operation & Maintenance
mechanism for MPLS networks", February 2004.
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[IEEE802.3ah] IEEE 802.3, "IEEE Standard for Information
technology -
Local and metropolitan area networks - Carrier sense
multiple access with collision detection (CSMA/CD)
access method and physical layer specifications",
clause 57, December 2008.
[ITU-T-G.806] ITU-T Recommendation G.806, "Characteristics of
transport equipment - Description methodology and
generic functionality", January 2009.
[ITU-G8113.2] ITU-T Recommendation G.8113.2/Y.1372.2, "Operations,
administration and maintenance mechanisms for MPLS-TP
networks using the tools defined for MPLS", November
2012.
[ITU-G8113.1] ITU-T Recommendation G.8113.1/Y.1372.1, "Operations,
Administration and Maintenance mechanism for MPLS-TP
in Packet Transport Network (PTN)", November 2012.
Authors' Addresses
Tal Mizrahi
Marvell
6 Hamada St.
Yokneam, 20692
Israel
Email: talmi(_at_)marvell(_dot_)com
Nurit Sprecher
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Email: nurit(_dot_)sprecher(_at_)nsn(_dot_)com
Elisa Bellagamba
Ericsson
6 Farogatan St.
Stockholm, 164 40
Sweden
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Phone: +46 761440785
Email: elisa(_dot_)bellagamba(_at_)ericsson(_dot_)com
Yaacov Weingarten
34 Hagefen St.
Karnei Shomron, 4485500
Israel
Email: wyaacov(_at_)gmail(_dot_)com
draft-ietf-opsawg-oam-overview authors,
Here is my feedback on this document.
1.
Is this document in line with
http://tools.ietf.org/html/draft-ietf-trill-oam-req-04?
* For example, the following definitions could be reused.
Fault: The term Fault refers to an inability to perform a required
action, e.g., an unsuccessful attempt to deliver a packet.
Defect: The term Defect refers to an interruption in the normal
operation, such that over a period of time no packets are delivered
successfully.
Failure: The term Failure refers to the termination of the required
function over a longer period of time. Persistence of a defect for a
period of time is interpreted as a failure.
* For example, on the basic abstract
Abstract
Operations, Administration, and Maintenance (OAM) is a general term
that refers to a toolset that can be used for fault detection and
isolation, and for performance measurement. OAM mechanisms have been
defined for various layers in the protocol stack, and are used with a
variety of protocols.
Abstract (draft-ietf-trill-oam-req-04)
OAM (Operations, Administration and Maintenance) is a general term
used to identify functions and toolsets to troubleshoot and monitor
networks. This document presents, OAM Requirements applicable to
TRILL.
So, as an example: does OAM include function?
I advice to review draft-ietf-trill-oam-req-04
2.
draft-ietf-trill-oam is not mentioned, while the abstract mentions:
This document presents an overview of the OAM mechanisms that have
been defined and are currently being defined by the IETF.
Search for OAM in the current draft names (https://datatracker.ietf.org/), and
you will find many references.
Ok, I see later on:
This document focuses on IETF
documents that have been published as RFCs, while other ongoing OAM-
related work is outside the scope.
Ok, fine then: we don't need a reference to all the drafts.
However, draft-ietf-trill-oam is closed to be a RFC, and should be mentioned.
3.
Section 1
The term OAM in this document refers to Operations, Administration
and Maintenance [OAM-Def
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#ref-OAM-Def>],
focusing on the forwarding plane of OAM.
What does it mean "focusing on the forwarding plane of OAM"?
Do you take a subset of the definition for this document?
Btw, I don't see a definition in the terminology section.
In section 2.2.3
A Maintenance Point (MP) is a functional entity that is defined at a
node in the network, and either initiates or reacts to OAM messages.
Which plane is MP?
4.
Section 1, Introduction
"Hence, management aspects are outside the scope of this document."
I don't understand which management aspects we speak about here.
5.
Clarifying question regarding 1.2
If speak about OWAMP or TWAMP 'synthetic traffic), is that data plane,
control plane, or management plane?
Note that I found later on in the draft:
OWAMP and TWAMP use two separate protocols: a Control plane protocol,
and a Test plane protocol.
Interestingly enough, after reading the document, I reviewed
http://datatracker.ietf.org/doc/draft-ietf-opsawg-oam-overview/ballot/, and
saw the same feedback from Stewart Bryant:
Provide a clear view of OAM functionality and its relationship
to various "planes" of networking (data plane, control plane,
management plane). In particular, the importance of
fate-sharing of OAM and user traffic flows in packet networks
should be explained.
6.
I see a multiplication of "plane" terms in the IETF document, and in this
document in particular.
I could find: forwarding plane, management plane, control plane, data plane,
user plane, and test plane.
Way too many.
Please be consistent
7.
Table 1 summarizes the IETF OAM related RFCs discussed in this
document.
Table 2 summarizes the OAM standards mentioned in this document.
You need to change the Table 2 description. Do you want to say something along
the lines of:
Table 2 summarizes the OAM standards specified by other Standard
Development Organization
(SDO) than the IETF, along with IETF references where applicable.
8.
Section 2.2.1
For a formal definition of each term, refer to the references at the end of
this document.
Without a reference to a specific RFC, this is the type of statement which is
not useful: you have 5 pages of references.
You position this document as "An Overview of Operations, Administration, and
Maintenance (OAM) Mechanisms", but you tell the reader: "if you want to know about
the terms,
just read first all references!"
9.
You specify some terms and some OAM categories,
2.2.2
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#section-2.2.2>. OAM
Maintenance Entities ..........................13
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#page-13>
2.2.3
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#section-2.2.3>. OAM
Maintenance Points ............................14
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#page-14>
2.2.4
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#section-2.2.4>.
Proactive and On-demand activation ................15
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#page-15>
2.2.5
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#section-2.2.5>.
Connectivity Verification and Continuity Checks ...15
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#page-15>
2.2.6
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#section-2.2.6>.
Failures ..........................................15
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#page-15>
... but you don't use them in the section 3
Just_one_example with section 3.2.2
-
o Demand mode: in this mode, BFD control packets are sent on-demand.
Upon need, a system initiates a series of BFD control packets to
verify the liveness of the session
Instead of liveness, you have defined Connectivity Verification and Continuity
Checks in section 2.2.5
- OLD:
Each of the end-points of the monitored path maintains its own
session identification
NEW:
Each of the MEP maintains its own session identification
OR NEW (actually I don't know)
Each of the MP maintains its own session identification
- OLD
A BFD echo packet is sent to a peer system
Peer system = MEP, MP, or something else?
- etc...
10.
This document is composed of a list of OAM content and references, but I'm really missing
the document "scope and target audience".
When we did RFC 6632, which is the companion document, we
hadhttp://tools.ietf.org/html/rfc6632#section-1.1
The target audience of the document is, on the one hand, IETF working
groups, which aim to select appropriate standard management protocols
and data models to address their needs concerning network management.
On the other hand, the document can be used as an overview and
guideline by non-IETF Standards Development Organizations (SDOs)
planning to use IETF management technologies and data models for the
realization of management applications. The document can also be
used to initiate a discussion between the bodies with the goal to
gather new requirements and to detect possible gaps. Finally, this
document is directed to all interested parties that seek to get an
overview of the current set of the IETF network management protocols
such as network administrators or newcomers to the IETF.
You should have something similar.
11.
Section 3.6.1, put the paragraph 2 at the end of the section. The "alternative"
in the following sentence would then make sense
Alternative protocols for performance measurement are defined, for
example, in MPLS-TP OAM ([MPLS-LM-DM
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#ref-MPLS-LM-DM>],
[TP-LM-DM
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#ref-TP-LM-DM>]), and in
Ethernet
OAM [ITU-T-Y1731
<http://tools.ietf.org/html/draft-ietf-opsawg-oam-overview-08#ref-ITU-T-Y1731>].
My conclusions: this document still needs some work
Regards, Benoit
The IESG has received a request from the Operations and Management Area
Working Group WG (opsawg) to consider the following document:
- 'An Overview of Operations, Administration, and Maintenance (OAM)
Mechanisms'
<draft-ietf-opsawg-oam-overview-08.txt> as Informational RFC
The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf(_at_)ietf(_dot_)org mailing lists by 2013-01-25. Exceptionally, comments
may be
sent toiesg(_at_)ietf(_dot_)org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.
Abstract
Operations, Administration, and Maintenance (OAM) is a general term
that refers to a toolset that can be used for fault detection and
isolation, and for performance measurement. OAM mechanisms have been
defined for various layers in the protocol stack, and are used with a
variety of protocols.
This document presents an overview of the OAM mechanisms that have
been defined and are currently being defined by the IETF.
The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-opsawg-oam-overview/
IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-opsawg-oam-overview/ballot/
No IPR declarations have been submitted directly on this I-D.