Network Working Group N. Sprecher, Ed.
Internet-Draft Nokia Siemens Networks
Intended status: Informational T. Nadeau, Ed.
Expires: November 11, 2009 BT
H. van Helvoort, Ed.
Huawei
Y. Weingarten
Nokia Siemens Networks
May 10, 2009
MPLS-TP OAM Analysis
draft-sprecher-mpls-tp-oam-analysis-04.txt
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Abstract
The intention of this document is to analyze the set of requirements
for Operations, Administration, and Maintenance (OAM) for the
Transport Profile of MPLS(MPLS-TP) as defined in [MPLS-TP OAM Reqs],
to evaluate whether existing OAM tools (either from the current MPLS
toolset or from the ITU-T documents) can be applied to these
requirements. Eventually, the purpose of the document is to
recommend which of the existing tools should be extended and what new
tools should be defined to support the set of OAM requirements for
MPLS-TP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. LSP Ping . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. MPLS BFD . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. PW VCCV . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. ITU Recommendation Y.1731 . . . . . . . . . . . . . . . . 7
1.5. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.6. Organization of the document . . . . . . . . . . . . . . . 8
2. Architectural requirements and general principles of
operation . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1. Architectural and Principles of Operation -
Recommendations and Guidelines . . . . . . . . . . . . . . 11
3. MPLS-TP OAM Functions . . . . . . . . . . . . . . . . . . . . 12
3.1. Continuity Check and Connectivity Verification . . . . . . 12
3.1.1. Existing tools . . . . . . . . . . . . . . . . . . . . 12
3.1.2. Gap analysis . . . . . . . . . . . . . . . . . . . . . 13
3.1.3. Recommendations and Guidelines . . . . . . . . . . . . 14
3.2. Alarm Notification . . . . . . . . . . . . . . . . . . . . 14
3.2.1. Existing tools . . . . . . . . . . . . . . . . . . . . 14
3.2.2. Recommendations and Guidelines . . . . . . . . . . . . 14
3.3. Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3.1. Existing tools . . . . . . . . . . . . . . . . . . . . 15
3.3.2. Recommendations and Guidelines . . . . . . . . . . . . 15
3.4. Adjacency and Route Tracing . . . . . . . . . . . . . . . 15
3.4.1. Existing tools . . . . . . . . . . . . . . . . . . . . 15
3.4.2. Recommendations and Guidelines . . . . . . . . . . . . 15
3.5. Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.5.1. Existing tools . . . . . . . . . . . . . . . . . . . . 16
3.5.2. Recommendations and Guidelines . . . . . . . . . . . . 16
3.6. Remote Defect Indication . . . . . . . . . . . . . . . . . 16
3.6.1. Existing tools . . . . . . . . . . . . . . . . . . . . 16
3.6.2. Recommendations and Guidelines . . . . . . . . . . . . 16
3.7. Client Fail Indication . . . . . . . . . . . . . . . . . . 17
3.7.1. Existing tools . . . . . . . . . . . . . . . . . . . . 17
3.7.2. Recommendations and Guidelines . . . . . . . . . . . . 17
3.8. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 17
3.8.1. Existing tools . . . . . . . . . . . . . . . . . . . . 17
3.8.2. Recommendations and Guidelines . . . . . . . . . . . . 18
3.9. Delay Measurement . . . . . . . . . . . . . . . . . . . . 18
3.9.1. Existing tools . . . . . . . . . . . . . . . . . . . . 18
3.9.2. Recommendations and Guidelines . . . . . . . . . . . . 19
4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 19
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
8. Informative References . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
OAM (Operations, Administration, and Maintenance) plays a significant
and fundamental 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.
[MPLS-TP Reqs] in general, and [MPLS-TP OAM Reqs] in particular
define a set of requirements for OAM functionality in MPLS-Transport
Profile (MPLS-TP) for MPLS-TP Label Switched Paths (LSPs) (network
infrastructure) and Pseudowires (PWs) (services).
The purpose of this document is to analyze the OAM requirements and
evaluate whether existing OAM tools defined for MPLS can be used to
meet the requirements, identify which tools need to be extended to
comply with the requirements, and which new tools need to be defined.
We also take the ITU-T OAM toolset, as defined in [Y.1731], as a
candidate to base these new tools upon. The existing tools that are
evaluated include LSP Ping (defined in [LSP Ping]), MPLS Bi-
directional Forwarding Detection (BFD) (defined in [MPLS BFD]) and
Virtual Circuit Connectivity Verification (VCCV) (defined in [PW
VCCV] and [VCCV BFD]), and the ITU-T OAM toolset defined in [Y.1731].
1.1. LSP Ping
LSP Ping is a variation of ICMP Ping and traceroute [ICMP]] adapted
to the different needs of MPLS LSP. Forwarding, of the LSP Ping
packets, is based upon the LSP Label and label stack, in order to
guarantee that the echo messages are switched in-band (i.e. over the
same data route) of the LSP. However, it should be noted that the
messages are transmitted using IP/UDP encapsulation and IP addresses
in the 127/8 (loopback) range. The use of the loopback range
guarantees that the LSP Ping messages will be terminated, by a loss
of connectivity or inability to continue on the path, without being
transmitted beyond the LSP. The return message of the LSP Ping could
be sent either on the return LSP of a corouted bidirectional LSP, or
for associated bidirectional LSPs or unidirectional LSPs may be sent
using IP forwarding to the IP address of the LSP ingress node.
LSP Ping extends the basic ICMP Ping operation (of data-plane
connectivity and continuity check) 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 succesfully traversed before
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the faulty link or node. LSP Ping is not dependent on the MPLS
control-plane for its operation, i.e. even though the propagation of
the LSP label may be performed over the control-plane via the Label
Distribution Protocol (LDP).
LSP Ping can be activated both in on-demand and pro-active
(asynchronous) modes, as defined in [MPLS-TP OAM Reqs].
[P2MP LSP Ping] clarifies the applicability of LSP Ping to MPLS P2MP
LSPs, and extends the techniques and mechanisms of LSP Ping to the
MPLS P2MP environment.
[MPLS LSP Ping] extends LSP Ping to operate over MPLS tunnels or for
a stitched LSP.
As pointed out above, TTL exhaust is the method used to terminate
flows at intermediate LSRs, usually to locate a problem that was
discovered previously.
Some of the drawbacks identified with LSP Ping include - LSP Ping is
considered to be computational intensive as pointed out in [MPLS
BFD]. Use of the loopback address range (to protect against leakage
outside the LSP) assumes that all of the intermediate nodes support
some IP functionality. When LSP bundling is employed in the network,
there is no guarantee that the LSP Ping packets will follow the same
physical path used by the data traffic.
1.2. MPLS BFD
BFD (Bidirectional Forwarding Detection) is a mechanism that is
defined for fast fault detection for point-to-point connections. BFD
defines a simple packet that may be transmitted over any protocol,
dependent on the application that is employing the mechanism. BFD is
dependent upon creation of a session that is agreed upon by both ends
of the link (which may be a single link, LSP, etc.) that is being
checked. The session is assigned a separate identifier by each end
of the path being monitored. This session identifier is by nature
only unique within the context of node that assigned it. As part of
the session creation, the end-points negotiate an agreed transmission
rate for the BFD packets. BFD supports an echo function to check the
continuity, and verify the reachability of the desired destination.
BFD does not support neither a discovery mechanism nor a traceroute
capability for fault localization, these must be provided by use of
other mechanisms. The BFD packets support authentication between the
routers being checked.
BFD can be used in pro-active (asynchronous) and on-demand modes, as
defined in [MPLS-TP OAM Reqs], of operation.
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[MPLS BFD] defines the use of BFD for P2P LSP end-points and is used
to verify data-plane continuity. It uses a simple hello protocol
which can be easily implemented in hardware. The end-points of the
LSP exchange hello packets at negotiated regular intervals and an
end-point is declared down when expected hello packets do not show
up. Failures in each direction can be monitored independently using
the same BFD session. The use of the BFD echo function and on-demand
activation are outside the scope of the MPLS BFD specification.
The BFD session mechanism requires an additional (external) mechanism
to bootstrap and bind the session to a particular LSP or FEC. LSP
Ping is designated by [MPLS BFD] as the bootstrap mechanism for the
BFD session in an MPLS environment. The implication is that the
session establishment BFD messages for MPLS are transmitted using a
IP/UDP encapsulation.
In order to be able to identify certain extreme cases of mis-
connectivity, it is necessary that each managed connection have its
own unique identifiers. BFD uses Discriminator values to identify
the connection being verified, at both ends of the path. These
discriminator values are set by each end-node to be unique only in
the context of that node. This limited scope of uniqueness would not
identify a misconnection of crossing paths that could assign the same
discriminators to the different sessions.
1.3. PW VCCV
PW VCCV provides end-to-end fault detection and diagnostics 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 sending 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 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.
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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.
1.4. ITU Recommendation Y.1731
[Y.1731] specifies a set of OAM procedures and related packet data
unit (PDU) formats that meet the transport network requirements for
OAM. These PDU and procedures address similar requirements to those
outlined in [MPLS-TP OAM Reqs].
The PDU and procedures are described relative to an Ethernet
environment, with the appropriate encapsulation for that environment.
However, the actual PDU formats are technology agnostic and could be
carried over different encapsulations, e.g. VCCV control channel.
The OAM procedures, likewise, could be supported by MPLS-TP nodes
just as they are supported by Ethernet nodes.
[Y.1731] describes procedures to support the following OAM functions:
o Connectivity and Continuity Monitoring - for end-to-end checking
o Loopback functionality - to verify connectivity to intermediate
nodes
o Link trace - provides information on the intermediate nodes of the
path being monitored, may be used for fault localization.
o Alarm indication signaling - for alarm suppression in case of
faults that are detected at the server layer.
o Remote defect indication &ndash as part of the Connectivity and
Continuity Monitoring packets
o Performance monitoring - including measurement of packet delays
both uni and bi-directional, measurement of the ratio of lost
packets, and the effective bandwidth that is supported without
packet loss.
It should be noted that the PDU defined in [Y.1731] includes various
information elements (fields) that may not be defined in [MPLS-TP OAM
Framework]. These fields include information on the MEG-Level,
OpCode, and version. Addressing of the PDU as defined in [Y.1731] is
based on the MAC Address of the nodes, which would need to be
adjusted to support other addressing schemes, length of additional
information. The addressing information is carried in <Type, Length,
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Value> (TLV) fields that follow the actual PDU.
1.5. Acronyms
This draft uses the following acronyms:
+---------+------------------------------------------------+
| AC | Attachment Circuit |
| ACH | Associated Channel Header |
| BFD | Bidirectional Forwarding Detection |
| CC-V | Continuity Check and Connectivity Verification |
| FEC | Forwarding Equivalence Class |
| LDP | Label Distribution Protocol |
| LSP | Label Switched Path |
| ME | Maintenance Entitity |
| MEP | Maintenance End Point |
| MIP | Maintenance Intermediate Point |
| MPLS-TP | Transport Profile for MPLS |
| OAM | Operations, Administration, and Maintenance |
| PDU | Packet Data Unit |
| PW | Pseudowire |
| RDI | Remote Defect Indication |
| SLA | Service Level Agreement |
| TC | Tandem Connection |
| TCME | Tandem Connection Maintenance Entity |
| TTL | Time-to-live |
| VCCV | Virtual Circuit Connectivity Verification |
| VPCV | Virtual Path Connectivity Verification |
+---------+------------------------------------------------+
1.6. Organization of the document
Section 2 of the document analyzes the requirements that are
documented in [MPLS-TP OAM Reqs] and provides basic principles of
operation for the OAM functionality that is required.
Section 3 evaluates which existing tools can provide coverage for the
different OAM functions that are required to support MPLS-TP.
Section 4 provides recommendations on what functionality could be
covered by the existing toolset and what extensions or new tools
would be needed in order to provide full coverage of the OAM
functionality for MPLS-TP.
2. Architectural requirements and general principles of operation
[MPLS-TP OAM Reqs] defines a set of requirements on OAM architecture
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and general principles of operations which are evaluated below:
o [MPLS-TP OAM Reqs] requires that OAM mechanisms in MPLS-TP are
independent of the transmission media and of the client service
being emulated by the PW. The existing tools comply with this
requirement.
o [MPLS-TP OAM Reqs] requires that MPLS-TP OAM MUST be able to
operate without IP functionality and without relying on control
and/or management planes. It is required that OAM functionality
MUST NOT be dependent on IP routing and forwarding capabilities.
The existing tools do not rely on control and/or management plane,
however the following should be observed regarding the reliance on
IP functionality:
* LSP Ping, VCCV Ping, and MPLS BFD makes use of IP header
(UDP/IP) and do not comply with the requirement. In the on-
demand mode, LSP Ping also uses IP forwarding to reply back to
the source router. This dependence on IP, has further
implications concerning the use of LSP Ping as the bootstrap
mechanism for BFD for MPLS.
* VCCV BFD supports the use of PW-ACH encapsulated BFD sessions
for PWs and can comply with the requirement.
* Y.1731 PDU are technology agnostic and thereby not dependent on
IP functionality. These PDU could be carried by a VCCV control
channel.
o [MPLS-TP OAM Reqs] requires that OAM tools for fault management do
not rely on user traffic, and the existing MPLS OAM tools and
Y.1731 already comply with this requirement.
o It is also required that 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 ones.
* For PWs, VCCV provides a control channel that can be associated
with each PW which allows sending OAM packets in band of PWs
and allow the receiving end-point to intercept, interpret, and
process them locally as OAM messages. VCCV defines different
VCCV Connectivity Verification Types for MPLS (like ICMP Ping,
LSP Ping and IP/UDP encapsulated BFD and PW-ACH encapsulated
BFD).
* Currently there is no distinct OAM payload identifier in MPLS
shim. BFD and LSP Ping packets for LSPs are carried over
UDP/IP and are addressed to the loopback address range. The
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router at the end-point intercepts, interprets, and processes
the packets.
* The Y.1731 PDU could be carried over a control channel defined
along the data path and the processing of the PDU would occur
at the destination indicated in the PDU.
o [MPLS-TP OAM Reqs] requires that the MPLS-TP OAM mechanism allows
the propagation of AC (Attachment Circuit) failures and their
clearance across a MPLS-TP domain
* BFD for VCCV supports a mechanism for "Fault detection and
AC/PW Fault status signaling." This can be used for both IP/
UDP encapsulated or PW-ACH encapsulated BFD sessions, i.e. by
setting the appropriate VCCV Connectivity Verification
Type.This mechanism could support this requirement.
o [MPLS-TP OAM Reqs] defines Maintenance Domain, Maintenance End
Points (MEPs) and Maintenance Intermediate Points (MIPs). Means
should be defined to provision these entities, both by static
configuration (as it is required to operate OAM in the absence of
any control plane or dynamic protocols) and by a control plane.
Note that the Y.1731 functionality currently supports these
entities.
o [MPLS-TP OAM Reqs] requires a single OAM technology and consistent
OAM capabilities for LSPs, PWs, MPLS-TP Links, and Tandem
Connections. There is currently no mechanism in the IETF to
support OAM for Tandem Connections. Also, the existing set of
tools defines a different way of operating the OAM functions (e.g.
LSP Ping to bootstrap MPLS BFD vs. VCCV). Currently, the Y.1731
functionality is defined for Ethernet paths, and the procedures
would need to be redefined for the various MPLS-TP path concepts.
o [MPLS-TP OAM Reqs] requires allowing OAM packets to be directed to
an intermediate node (MIP) of a LSP/PW. Technically, this could
be supported by the proper setting of the TTL value. However, the
applicability of such a solution needs to be examined per OAM
function. For details, see below.
o [MPLS-TP OAM Reqs] suggests that OAM messages MAY be
authenticated. BFD has a support for authentication. Other tools
should support this capability as well. Y.1731 functionality uses
the identification of the path for authentication.
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2.1. Architectural and Principles of Operation - Recommendations and
Guidelines
Based on the requirements analysis above, the following guidelines
should be followed to create an OAM environment that could more fully
support the requirements cited:
o Extend the PW Associate Channel Header (ACH) to provide a control
channel at the path and section levels. This could then be
associated with a MPLS-TP Link, LSP, or a Tandem Connection (TC).
The ACH should then become a common mechanism for PW, LSP, MPLS-TP
Link, and Tandem Connection.
o Create a VPCV (Virtual Path Connectivity Verification) definition
that would apply the definitions and functionality of VCCV to the
MPLS-TP environment for LSP or Tandem Connection. Need a
generalized addressing scheme that can also support unique
identification of the monitored paths (or connections).
o Create or extend the VCCV definition to define a mechanism that
would apply the definitions and functionality of VCCV to PW Tandem
Connections
o Apply BFD to these new mechanisms using the control channel
encapsulation, as defined above - allowing use of BFD for MPLS-TP
independent of IP functionality. This could be used to address
the CC-V functionality
o The Y.1731 PDU set could be used as a basis for defining the
information units to be transmitted over the VPCV. The actual
procedures and addressing schemes would need to be adjusted for
the MPLS-TP environment.
o Define a mechanism to create TCME and allow transmission of the
traffic via the Tandem Connection using label stacking.
o Define a mechanism that could be used to address a MIP of a path
in a unique way, to support the maintenance functions. This
addressing should be flexible to allow support for different
addressing schemes, and would supplement the TTL addressing of
intermediate points.
Creating these extensions/mechanisms would fulfill the following
architectural requirements, mentioned above:
o Independence of IP forwarding and routing.
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o OAM packets should be transmitted in-band.
o Support a single OAM technology for LSP, PW, MPLS-TP Link, and TC.
In addition, the following additional requirements can be satisfied:
o Provide the ability to carry other types of communications (e.g.,
APS, Management Control Channel (MCC), Signalling Control Channel
(SCC)), by defining new types of communication channels for PWs,
MPLS-TP Links, and LSPs.
o The design of the OAM mechanisms for MPLS-TP MUST allow the
ability to support vendor specific and experimental OAM functions.
3. MPLS-TP OAM Functions
The following sections discuss the required OAM functions that were
identified in [MPLS-TP OAM Reqs].
LSP Ping is not considered a candidate to fulfill the required
functionality, due its failure to comply with the basic architectural
requirement for independence from IP routing and forwarding, as
documented in Section 2 of this document. However, usage of LSP
Ping, in addition to the MPLS-TP OAM tools, or in MPLS-TP deployments
with IP functionality is not precluded.
3.1. Continuity Check and Connectivity Verification
Continuity Check and Connectivity Verification (CC-V) are OAM
operations generally used in tandem, and compliment each other.
Together they are used to detect loss of traffic continuity and
misconnections between MEPs and are useful for applications like
Fault Management, Performance Monitoring and Protection Switching,
etc. To guarantee that CC-V can identify misconnections from cross-
connections it is necessary that the tool use network-wide unique
identifiers for the path that is being checked in the session.
3.1.1. Existing tools
LSP Ping provides much of the functionality required for corouted
bidirectional LSPs. As observed above, LSP Ping may be operated in
both asynchronous and on-demand mode. Addressing is based on the LSP
label and the basic functionality only requires support for the
loopback address range in each node on the LSP path.
BFD defines functionality that can be used to support the pro-active
OAM CC-V function when operated in the asynchronous mode. However,
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the current definition of basic BFD is dependent on use of LSP Ping
to bootstrap the BFD session. Regarding the connectivity functional
aspects, basic BFD has a limitation that it uses only locally unique
(to each node) session identifiers.
VCCV can be used to carry BFD packets that are not IP/UDP
encapsulated for CC-V on a PW and use the PW label to identify the
path.
Y.1731 provides functionality for all aspects of CC-V for an Ethernet
environment, this could be translated for the MPLS-TP environment.
The CCM PDU defined in [Y.1731] includes the ability to set the
frequency of the messages that are transmitted, and provides for
attaching the address of the path (in the Ethernet case - the MEG
Level) and a sequencing number to verify that CCM messages were not
dropped.
3.1.2. Gap analysis
There is currently no single MPLS tool that gives coverage for all
aspects of CC-V functionality.
LSP Ping could be used to cover the cases of corouted bidirectional
LSPs. However, there is a certain amount of computational overhead
involved with use of LSP Ping (as was observed in sec 1.1), the
verification of the control-plane, and the need to support the
loopback functionality at each intermediate node.
BFD could be extended to fill the gaps indicated above. The
extension would include:
o A mechanism should be defined to carry BFD packets over LSP
without reliance on IP functionality.
o A mechanism should be defined to bootstrap BFD sessions for MPLS
that is not dependent on UDP.
o BFD needs to be used in conjunction with "globally" unique
identifiers for the path or ME being checked to allow connectivity
verfication support. There are two possibilities, to allow BFD to
support this new type of identifier -
* Change the semantics of the two Discriminator fields that exist
in BFD and have each node select the ME unique identifier.
This may have backward compatibility implications.
* Create a new optional field in the packet carrying the BFD that
would identify the path being checked, in addition to the
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existing session identifiers.
o Extensions to BFD would be needed to cover P2MP connections.
Use of the Y.1731 functionality is another option that should be
considered. The basic PDU for CCM includes (in the flags field) an
indication of the frequency of the packets [eliminating the need to
"negotiate" the frequency between the end-points], and also a flag
used for RDI. The procedure itself would need adaptation to comply
with the MPLS environment.
An additional option would be to create a new tool that would give
coverage for both aspects of CC-V according to the requirements and
the principles of operation (see section 2.1). This option is less
preferable.
3.1.3. Recommendations and Guidelines
Extend BFD to resolve the gaps, using a new optional field for the
unique path identifier. And optionally support the PDU format
defined in [Y.1731] with appropriate adjustments to support the
MPLS-TP architecture.
Note that [MPLS BFD] defines a method for using BFD to provide
verification of multipoint or multicast connectivity.
3.2. Alarm Notification
Alarm Notification is a function that is used by a server layer MEP
to notify a failure condition to its client layer MEP(s) in order to
suppress alarms that may be generated by maintenance domains of the
client layer as a result of the failure condition in the server
layer. This function should also have the capability to
differentiate an administrative lock from a failure condition at a
different execution level.
3.2.1. Existing tools
There is no mechanism defined in the IETF to support this function.
Y.1731 does define a PDU and procedure for this functionality.
3.2.2. Recommendations and Guidelines
Define a tool to support Alarm Notification. This tool could be
designed around the PDU proposed by [Y.1731] that includes support
for an indication of the frequency at which these messages are
transmitted after the alarm is raised until it is cleared.
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3.3. Diagnostic
A diagnostic test is a function that is used between MEPs to verify
bandwidth throughput, packet loss, bit errors, etc. This is usually
performed by sending packets of varying sizes at increasing rates
(until the limits of the service level) to measure the actual
utilization.
3.3.1. Existing tools
There is no mechanism defined in the IETF to support this function.
[Y.1731] describes a function that is dependent on sending a series
of TST packets (this is a PDU whose size can be varied) at differing
frequencies.
3.3.2. Recommendations and Guidelines
Define a tool to support Diagnostic that could be based on the Y.1731
function.
3.4. Adjacency and Route Tracing
Functinality of route determination is used to determine the route of
a connection across the MPLS transport network. [MPLS-TP OAM Reqs]
defines two closely related operations - one, Adjacency, for
discovery of neighboring nodes and the other, Route Tracing, for
determination of the path that is being traversed and location of a
fault identified by e.g. the CC-V tool.
3.4.1. Existing tools
LSP Ping supports a trace route function that could be used for co-
routed bidirectional paths. This could support the second type of
fnctionality.
However, the discovery aspect that is described by the Adjacency
function does not have any available tools, neither in the IETF
toolset nor in the ITU recommendations.
3.4.2. Recommendations and Guidelines
Define a new tool to support the Adjacency functionality.
For the Route Trace functionality, either extend the LSP Ping
functionality to support other options, i.e. PW, associated
bidirectional LSP, or define a new tool.
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3.5. Lock
The Lock function allows the system to block off transmission of data
along a LSP. When a path end-point receives a command, e.g. from the
management system, that the path is blocked, the end-point informs
the far-end that the path has been locked and that no data should be
transmitted. This function is used on-demand.
3.5.1. Existing tools
There is no mechanism defined in the IETF to support this function.
Y.1731 does define a PDU and procedure for this functionality.
3.5.2. Recommendations and Guidelines
Define a tool to support Lock. This tool could be designed around
the procedure proposed by [Y.1731] that includes support for an
indication of the frequency at which these messages are transmitted
until the lock situation is cleared.
3.6. Remote Defect Indication
Remote Defect Indication (RDI) is used by a MEP to notify its peer
MEP that a defect, usually a unidirectional defect, is detected on a
bi-directional connection between them.
This function should be supported in pro-active mode.
3.6.1. Existing tools
There is no mechanism defined in the IETF to fully support this
functionality, however BFD supports a mechanism of informing the far-
end that the session has gone down, and the Diagnostic field
indicates the reason. Similarly, when LSP Ping is used for a
corouted bidirectional LSP the far-end LER could notify that there
was a misconnectivity.
In [Y.1731] this functionality is defined as part of the CC-V
function as a flag in the PDU.
3.6.2. Recommendations and Guidelines
Either create a dedicated mechanism for this functionality or extend
the BFD session functionality to support the functionality without
disrupting the CC or CV functionality. Such an extension could be
similar to that suggested by the ITU recommendation
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3.7. Client Fail Indication
Client Fail Indication (CFI) function is used to propagate an
indication of a failure to the far-end sink when alarm suppression in
the client layer is not supported.
3.7.1. Existing tools
There is a possibility of using the BFD over VCCV mechanism for
"Fault detection and AC/PW Fault status signalling". However, there
is a need to differentiate between faults on the AC and the PW.
3.7.2. Recommendations and Guidelines
Either extend the BFD tool or define a tool to support Client Fail
Indication propagation.
3.8. Packet Loss
Packet Loss is a function that is 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.
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.
3.8.1. Existing tools
There is no mechanism defined in the IETF to support this function.
[Y.1731] describes a function that is based on sending the CCM
packets [used for CC-V support (see sec 3.1)] for proactive support
and specialized loss-measurement packets for on-demand measurement.
These packets include information (in the additional TLV fields) of
packet counters that are maintained by each of the end-points of a
path. These counters maintain a count of packets transmitted by the
ingress end-point and the count of packets received from the far-end
of the path by the egress end-point.
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3.8.2. Recommendations and Guidelines
One possibility is to define a mechanism to support Packet Loss
Measurement, based on the delimiting messages. This would include a
way for delimiting the periods for monitoring the packet
transmissions to measure the loss ratios, and computation of the
ratio between received and transmitted packets.
A second possibility would be to define a functionality based on the
description of the loss-measurement function defined in [Y.1731] that
is dependent on the counters maintained, by the MPLS LSR (as
described in [RFC3813], of received and transmitted octets.
3.9. Delay Measurement
Delay Measurement is a function that is used to measure one-way or
two-way delay of a packet transmission between a pair of MEPs.
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 first 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
one of two ways -
o Using OAM packets - checking delay (either one-way or two-way) in
transmission of OAM packets. May not fully reflect delay of
larger packets, however, gives feedback on general service level.
o Using delimited periods of transmission - may be too intrusive on
the client traffic.
3.9.1. Existing tools
There is no mechanism defined in the IETF toolset that fulfills all
of the MPLS-TP OAM requirements.
[Y.1731] describes a function in which specific OAM packets are sent
with a transmission time-stamp from one end of the managed path to
the other end (these are transparent to the intermediate nodes). The
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delay measurement is supported for both unidirectional and
bidirectional measurement of the delay.
3.9.2. Recommendations and Guidelines
Define a mechanism that would allow to support Delay Measurement.
The mechanism should be based on measurement of the delay in
transmission and reception of OAM packets, transmitted in-band with
normal traffic. This tool could be based on the tool defined in
[Y.1731].
4. Recommendations
o Define a maintenance entity that could be applied both to LSPs and
PWs that would support management of a sub-path. This entity
should allow for transmission of traffic by means of label
stacking and proper TTL setting.
o Extend the control and the management planes to support the
configuration of the OAM maintenance entities and the set of
functions to be supported by these entities.
o Extend the ACH to provide a control channel for MPLS-TP Links,
LSPs, and Tandem Connections.
o Define a mechanism that would allow the unique addressing of the
elements that need to be monitored, e.g., the connections, MEPs,
and MIPs of a path. This mechanism needs to be flexible enough to
support different addressing schemes, e.g. IP addresses, NSAP,
connection names.
o Define a VPCV mechanism for LSP and Tandem Connection. This
mechanism should reuse, as much as possible, the same principles
of operation as VCCV. The ACH should be extended to support CV
types for each of the tools that are defined below, in a way that
is consistent for PW, LSP and Tandem Connection.
o The appropriate assignment of network-wide unique identifiers
needed to support connectivity verification should be considered.
o Tools should be defined to support the following functions. The
tools could be based on the procedures and PDU format defined by
[Y.1731] or extensions to existing MPLS tools:
* On-demand connectivity verification
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* Alarm suppression
* Packet loss measurement
* Diagnostic test
* Route determination
* Delay measurement
* Remote defect indication
* Client fail indication
o The tools may have the capability to authenticate the messages.
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
This document does not by itself raise any particular security
considerations.
7. Acknowledgements
The authors wish to thank xxxxxxx for his review and proposed
enhancements to the text.
8. Informative References
[ICMP] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, Sept 1981.
[LSP Ping]
Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[PW ACH] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
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"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
[PW VCCV] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[MPLS BFD]
Katz, D. and D. Ward, "BFD for Multipoint Networks",
ID draft-katz-ward-bfd-multipoint-01.txt, December 2007.
[VCCV BFD]
Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)",
ID draft-ietf-pwe3-vccv-bfd-01.txt, February 2008.
[P2MP LSP Ping]
Nadeau, T. and A. Farrel, "Detecting Data Plane Failures
in Point-to-Multipoint Multiprotocol Label Switching
(MPLS) - Extensions to LSP Ping",
ID draft-ietf-mpls-p2mp-lsp-ping-06.txt, June 2008.
[MPLS LSP Ping]
Bahadur, N. and K. Kompella, "Mechanism for performing
LSP-Ping over MPLS tunnels",
ID draft-ietf-mpls-lsp-ping-enhanced-dsmap-00, June 2008.
[MPLS-TP OAM Reqs]
Vigoureux, M., Betts, M., and D. Ward, "Requirements for
OAM in MPLS Transport Networks",
ID draft-ietf-mpls-tp-oam-requirements-01, April 2009.
[MPLS-TP OAM Frwk]
Busi, I. and B. Niven-Jenkins, "MPLS-TP OAM Framework and
Overview", ID draft-ietf-mpls-tp-oam-requirements-01,
March 2009.
[MPLS-TP Reqs]
Nadeau, T. and C. Pignataro, "Requirements for the
Trasport Profile of MPLS",
ID draft-ietf-mpls-tp-requirements-06, April 2009.
[RFC3813] Srinivasan, C., Viswanathan, A., and T. Nadeau,
"Multiprotocol Label Switching (MPLS) Label Switching
Router (LSR) Management Information Base (MIB)",
RFC 3813, June 2004.
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[Y.1731] International Telecommunications Union - Standardization,
"OAM functions and mechanisms for Ethernet based
networks", ITU Y.1731, May 2006.
Authors' Addresses
Nurit Sprecher (editor)
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Email: nurit.sprecher@nsn.com
Tom Nadeau (editor)
BT
United States
Email: tom.nadeau@bt.com
Huub van Helvoort (editor)
Huawei
Kolkgriend 38, 1356 BC Almere
Netherlands
Phone: +31 36 5316076
Email: hhelvoort@huawei.com
Yaacov Weingarten
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Phone: +972-9-775 1827
Email: yaacov.weingarten@nsn.com
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