Network Working Group A. Takacs
Internet-Draft Ericsson
Intended status: Standards Track D. Fedyk
Expires: June 26, 2009 Nortel
H. Jia
Huawei
December 23, 2008
OAM Configuration Framework and Requirements for GMPLS RSVP-TE
draft-ietf-ccamp-oam-configuration-fwk-00
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Abstract
OAM functions are essential to ensure that the desired service level
of traffic engineered connections are met. In certain technologies
OAM entities are inherently established once the connection is set
up. However other technologies, especially OAM for packet switched
networks, require an extra configuration step after connection
establishment to setup OAM entities. This document specifies
extensions to RSVP-TE to support the establishment and configuration
of OAM entities along with LSP signalling.
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. GMPLS RSVP-TE Extensions . . . . . . . . . . . . . . . . . . . 9
3.1. Operation overview . . . . . . . . . . . . . . . . . . . . 9
3.2. OAM entities desired -- LSP Attributes flag . . . . . . . 10
3.3. OAM Configuration TLV . . . . . . . . . . . . . . . . . . 11
3.4. Monitoring Disabled - Admin_Status bit . . . . . . . . . . 11
3.5. OAM configuration errors . . . . . . . . . . . . . . . . . 12
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix A. Discussion on alternatives . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
Operations and Management (OAM) functions are essential to ensure
that the desired service level of traffic engineered connections are
met. OAM functions ease network operation by reducing complexity,
enhance network survivability, verify network performance, and in
turn reduce operational costs.
In certain technologies OAM entities are inherently established once
the connection is set up. However other technologies, especially OAM
for packet switched networks, require an extra configuration step
after connection establishment to setup OAM entities.
In some situations the use of OAM functions, like those of Fault-
(FM) and Performance Management (PM), may be optional confirming to
actual network management policies. Hence the network operator must
be able to choose which kind of OAM functions to apply to specific
connections and with what parameters the selected OAM functions
should be configured and operated. To achieve this objective OAM
entities and specific functions must be selectively configurable.
The GMPLS control plane consists of a set of protocols: OSPF-TE,
RSVP-TE and LMP. which are used to reduce manual configuration and
improve management efficiency. RSVP-TE is used to setup and
configure end-to-end connections. A new useful application of
RSVP-TE is OAM configuration and control for transport networks.
When RSVP-TE is used for LSP establishment it is desirable to bind
OAM setup to connection establishment signalling to avoid two
separate management/configuration steps (connection setup followed by
OAM configuration) which increases delay, processing and more
importantly may be prune to misconfiguration errors.
The mechansim described in this document provides an additional
option for bootstrapping OAM that is not intended to replace or
deprecate the use of other OAM bootstrapping techniques such as LSP
Ping [RFC4379]. The procedures specified in this document are
intended only for use in environments where RSVP-TE signaling is
already in use to set up the LSPs that are to be monitored using OAM.
This document describes requirements on OAM configuration and control
via RSVP-TE, and specifies extensions to the RSVP-TE protocol
providing a framework to configure and control OAM entities along
with capability to carry technology specific information. Extensions
can be grouped into generic elements that are applicable to any OAM
solution and technology specific elements that provide additional
configuration parameters only needed for a specific OAM technology.
This document specifies the technology agnostic elements that alone
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can be used to establish OAM entities in the case no technology
specific information is needed, and specifies the way additional
technology specific OAM parameters are provided.
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2. Requirements
MPLS OAM requirements are described in [RFC4377]. It provides
requirements to create consistent OAM functionality for MPLS
networks. GMPLS OAM requirements are described in [GMPLS-OAM]. The
GMPLS OAM requirements are based on the MPLS OAM requirements
[RFC4377], in addition it also considers the existing OAM techniques
in non-packet networks.
The following list is an excerpt of MPLS OAM requirements documented
in [RFC4377]. Only a few requirements are discussed that bear a
direct relevance to the discussion set forth in this document.
o It is desired to support the automation of LSP defect detection.
It is especially important in cases where large numbers of LSPs
might be tested.
o In particular some LSPs may require automated ingress-LSR to
egress-LSR testing functionality, while others may not.
o Mechanisms are required to coordinate network responses to
defects. Such mechanisms may include alarm suppression,
translating defect signals at technology boundaries, and
synchronising defect detection times by setting appropriately
bounded detection timeframes.
MPLS-TP defines a profile of MPLS targeted at transport applications
[MPLS-TP-FWK]. This profile specifies the specific MPLS
characteristics and extensions required to meet transport
requirements, including providing additional OAM, survivability and
other maintenance functions not currently supported by MPLS.
Specific OAM requirements for MPLS-TP are specified in
[MPLS-TP-OAM-REQ]. MPLS-TP poses requirements on the control plane
to configure and control OAM entities.
o The use of OAM functions SHOULD be optional for the operator. A
network operator SHOULD be able to choose which OAM functions to
use and which Maintenance Entity to apply them to.
o The MPLS-TP control pane MUST support the configuration and
modification of OAM maintenance points as well as the activation/
deactivation of OAM when the transport path is established or
modified. OAM functions SHOULD be configurable as part of
connectivity (LSP or PW) management.
Ethernet Connectivity Fault Management (CFM) defines an adjunct
connectivity monitoring OAM flow to check the liveliness of Ethernet
networks [IEEE-CFM]. With PBB-TE [IEEE-PBBTE] Ethernet networks will
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support explicitly-routed Ethernet connections. CFM can be used to
track the liveliness of PBB-TE connections and detect data plane
failures. In IETF the GMPLS controlled Ethernet Label Switching
(GELS) [GELS-Framework] work is extending the GMPLS control plane to
support the establishment of point-to-point PBB-TE data plane
connections. Without control plane support separate management
commands would be needed to configure and start CFM.
GMPLS based OAM configuration and control should be general to be
applicable to a wide range of data plane technologies and OAM
solution. There are three typical data plane technologies used for
transport application, which are wavelength based such as WSON, TDM
based such as SDH/SONET, packet based such as MPLS-TP [MPLS-TP-FWK]
and Ethernet PBB-TE [IEEE-PBBTE]. In all these data planes, the
operator MUST be able to configure and control the following OAM
functions.
o It MUST be possible to explicitly request the setup of OAM
entities for the signalled LSP and provide specific information
for the setup if this is required by the technology.
o When periodic messages are used for liveliness check (continuity
check) of LSPs it MUST be possible to set the frequency of
messages allowing proper configuration for fulfilling the
requirements of the service and/or meeting the detection time
boundaries posed by possible congruent connectivity check
operations of higher layer applications. For a network operator
to be able to balance the trade-off in fast failure detection and
overhead it is beneficial to configure the frequency of continuity
check messages on a per LSP basis.
o Control of alarms is important to avoid false alarm indications
and reporting to the management system. It MUST be possible to
enable/disable alarms generated by OAM functions. In some cases
selective alarm control may be desirable when, for instance, the
operator is only concerned about critical alarms thus the non-
service affecting alarms should be inhibited.
o Performance Monitoring (PM) is continuously collecting information
about specific characteristics of the connection. It MUST be
possible to configure PM functions, e.g., set monitoring intervals
and thresholds for PM initiated alarms. For consistent
measurement of Service Level Agreements (SLAs) it may be required
that measurement points agree on a common probing rate to avoid
measurement problems.
o The extensions must allow the operator to use only a minimal set
of OAM configuration and control features if the data plane
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technology, the OAM solution or network management policy allows.
The extensions must be reusable as much as reasonably possible.
That is generic OAM parameters and data plane or OAM technology
specific parameters must be separated.
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3. GMPLS RSVP-TE Extensions
3.1. Operation overview
Two types of Maintenance Poits (MPs) are distinguished: Maintenance
End Points (MEPs) and Maintenance Intermediate Points (MIPs). MEPs
are located at the ends of an LSP and are capable of initiating and
terminating OAM packets for Fault Management (FM) and Performance
Monitoring (PM). MIPs on the other hand are located at transit nodes
of an LSP and are capable of reacting to some OAM packets but
otherwise do not initiate packets. Maintenance Entity (ME) refers to
an association of MEPs and MIPs that are provisioned to monitor an
LSP. The ME association is achieved by configuring MPs of an ME with
the same unique ME ID. Each MEP must have unique identification (MEP
ID) within the ME.
When an LSP is signalled forwarding association is established
between endpoints and transit nodes via label bindings. This
association creates a context for the OAM entities monitoring the
LSP. On top of this association OAM entities may be configured with
an ME ID and MEP IDs. The ME ID may be used to detect
misconfiguration errors and leacking OAM traffic. Within the ME the
MEP ID can be used to demultiplex and identify the originating MEP of
OAM packets. Since MIPs do not originate OAM packets no specific
configuration is required for them.
In addition to the ME and MEP identification parameters pro-active
OAM functions (e.g., Continuity Check (CC), Performance Monitoring)
may have specific parameters requiring configuration as well. In
particular, the frequency of periodic CC packets and the measurement
interval for loss and delay measurements may need to be configured.
MEP
+-------------+
|OAM Functions|
| FM | PM |
+------+------+
| MEP ID |
+-------------+
| ME ID |
+-------------+
+-------------+
| LSP |
+-------------+
In some cases all the above parameters may be either derived form
some exiting information or pre-configured default values can be
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used. In the simplest case the control plane needs to provide
information whether or not a ME with MPs need to be setup for the
signalled LSP. If OAM entities are created signalling must provide
means to activate/deactivate OAM message flows and associated alarms.
ME and MEP IDs as well as configuration of OAM functions are
technology specific, i.e., vary depending on the data plane
technology and the chosen OAM solution. In addition for any given
data plane technology a set of OAM solutions may be applicable. The
OAM configuration framework allows selecting a specific OAM solution
to be used for the signalled LSP and provides technology specific
TLVs to carry further detailed configuration information.
3.2. OAM entities desired -- LSP Attributes flag
In RSVP-TE the Flags field of the SESSION_ATTRIBUTE object is used to
indicate options and attributes of the LSP. The Flags field has 8
bits and hence is limited to differentiate only 8 options. [RFC4420]
defines a new object for RSVP-TE messages to allow the signalling of
arbitrary attribute parameters making RSVP-TE easily extensible to
support new applications. Furthermore, [RFC4420] allows options and
attributes that do not need to be acted on by all Label Switched
Routers (LSRs) along the path of the LSP. In particular, these
options and attributes may apply only to key LSRs on the path such as
the ingress LSR and egress LSR. Options and attributes can be
signalled transparently, and only examined at those points that need
to act on them. The LSP_ATTRIBUTES object and the
LSP_REQUIRED_ATTRIBUTES objects are defined in [RFC4420] to provide
means to signal LSP attributes and options in the form of TLVs.
Options and attributes signalled in the LSP_ATTRIBUTES object can be
passed transparently through LSRs not supporting a particular option
or attribute, while the contents of the LSP_REQUIRED_ATTRIBUTES
object must be examined and processed by each LSR. One TLV is
defined in [RFC4420]: the Attributes Flags TLV.
A new bit (10 IANA to assign): "OAM entities desired" is allocated in
the LSP Attributes Flags TLV. If the "OAM entities desired" bit is
set it is indicating that the establishment of OAM entities are
required at the endpoints of the signalled LSP. If the establishment
of OAM entities is not supported an error must be generated: "OAM
Problem/OAM establishment not supported".
If the "OAM entities desired" bit is set and additional parameters
are needed to configure the OAM entities an OAM Configuration TLV may
be included in the LSP_ATTRIBUTES object.
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3.3. OAM Configuration TLV
This TLV specifies which OAM technology/method should be used for the
LSP. The OAM Configuration TLV is carried in the LSP_ATTRIBUTES
object in Path messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (2) (IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAM Type | OAM Function | Reserved (set to all 0s) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: indicates a new type: the OAM Configuration TLV (2) (IANA to
assign).
OAM Type: specifies the technology specify OAM method. If the
requested OAM method is not supported an error must be generated:
"OAM Problem/Unsupported OAM Type".
This document defines no types. The receiving node based on the OAM
Type will check if a corresponding technology specific OAM
configuration TLV is included.
OAM Function Flags: specifies proactive OAM functions (e.g.,
connectivity monitoring, loss and delay measurement) that should be
established and configured. If the selected OAM Function(s) is(are)
not supported an error must be generated: "OAM Problem/Unsupported
OAM Function".
This document defines the following flags.
OAM Function Flag Description
--------------------- ---------------------------
0 Connectivity Monitoring
1-7 Reserved
3.4. Monitoring Disabled - Admin_Status bit
Administrative Status Information is carried in the ADMIN_STATUS
Object. The Administrative Status Information is described in
[RFC3471], the ADMIN_STATUS Object is specified for RSVP-TE in
[RFC3473].
One bit is allocated for the administrative control of OAM
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monitoring. In addition to the Reflect (R) bit, 7 bits are currently
occupied (assigned by IANA or temporarily blocked by work in progress
Internet drafts). As the 24th bit (IANA to assign) this draft
introduces the Monitoring Disabled (M) bit. When this bit is set the
monitoring and OAM triggered alarms of the LSP are disabled (e.g., no
continuity check messages are sent).
3.5. OAM configuration errors
To handle OAM configuration errors a new Error Code (IANA to assign)
"OAM Problem" is introduced. To refer to specific problems a set of
Error Values is defined.
If a node does not support the establishment of OAM entities via
RSVP-TE signalling it must use the error value (IANA to assign): "OAM
establishment not supported" in the PathErr message.
If a node does not support a specific OAM technology/solution it must
use the error value (IANA to assign): "Unsupported OAM Type" in the
PathErr message.
If a node does not support a specific OAM Function it must use the
error value (IANA to assign): "Unsupported OAM Function" in the
PathErr message.
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4. IANA Considerations
One bit (Monitoring Disabled (M)) needs to be allocated in the
ADMIN_STATUS Object.
One bit ("OAM entities desired") needs to be allocated in the LSP
Attributes Flag Registry.
This document specifies one new TLVs to be carried in the
LSP_ATTRIBUTES and LSP_REQUIRED_ATTRIBUTES objects in Path messages:
OAM Configuration TLV.
One new Error Code: "OAM Problem" and three new values: "OAM
establishment not supported", "Unsupported OAM Type" and "Unsupported
OAM Function" needs to be assigned.
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5. Security Considerations
The signalling of OAM related parameters and the automatic
establishment of OAM entities introduces additional security
considerations to those discussed in [RFC3473]. In particular, a
network element could be overloaded, if an attacker would request
liveliness monitoring, with frequent periodic messages, for a high
number of LSPs, targeting a single network element.
Security aspects will be covered in more detailed in subsequent
versions of this document.
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6. Acknowledgements
The authors would like to thank Francesco Fondelli, Adrian Farrel,
Loa Andersson, Eric Gray and Dimitri Papadimitriou for their useful
comments.
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Appendix A. Discussion on alternatives
This appendix summarises the discussions after IETF-71 about the way
OAM configuration information should be carried in RSVP-TE.
The first question is how the requirement for OAM establishment is
signalled and how the operation of OAM is controlled. There is a
straightforward way to achieve these using existing objects and
fields:
o Use one or more OAM flags in the LSP Attributes Flag TLV within
the LSP_ATTRIBUTES/LSP_REQUIRED_ATTRIBUTES object to signal that
OAM entities for the LSP need to be established. If for any
reason this cannot be done a notification is sent or an error is
raised.
o Once the LSP with the desired OAM entities is established OAM
operation may be controlled using one or more flags in the
ADMIN_STATUS object. For instance, the generation of connectivity
monitoring messages can be disabled/enabled by setting/clearing a
flag in the ADMIN_STATUS object.
However, there are two alternatives when it comes to signalling the
actual configuration parameters of OAM entities.
o Extension of the LSP_ATTRIBUTES object with new TLVs.
o Definition of a new RSVP-TE object to carry OAM information.
In the first case, a new OAM configuration TLV is defined in the
LSP_ATTRIBUTES object. This TLV would provide the detailed
information needed for LSPs with a set OAM flag in the LSP Attributes
Flag TLV. The rationale for this approach is that in addition to
setting flags the LSP_ATTRIBUTES object may carry complementary
information for all or some of the flags set. Furthermore, as top
level RSVP-TE objects may become scarce resources, it seems to be
beneficial not to allocate new RSVP-TE objects for the purpose of
providing detailed information for new LSP Attribute Flags.
Currently there is only one TLV, the Attributes Flag TLV, defined in
the LSP_ATTRIBUTES object. Defining a new TLV associated with one of
the flags would make a precedence and possibly be a guideline for
similar future extensions.
The other alternative would be to allocate a dedicated object for OAM
configuration information. The rationale for this is that the
complex information that may be required for OAM configuration would
unnecessarily add complexity to LSP_ATTRIBUTES/
LSP_REQUIRED_ATTRIBUTES objects and their processing mechanisms.
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Furthermore, traditionally RSVP uses dedicated objects (*_SPECs) to
carry configuration information of data plane entities, thus a new
object like an "OAM_SPEC" may be a better fit to existing protocol
elements.
The authors of this document favour the first alternative (adding new
TLVs to LSP_ATTRIBTES/LSP_REQUIRED_ATTRIBUTES. However, which
alternative to select for standardisation is up for the working group
to decide. In any case, the information to be carried would be the
same or very similar for both alternatives.
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7. References
[GELS-Framework]
"GMPLS Ethernet Label Switching Architecture and
Framework", Internet Draft, work in progress.
[GMPLS-OAM]
"OAM Requirements for Generalized Multi-Protocol Label
Switching (GMPLS) Networks", Internet Draft, work in
progress.
[IEEE-CFM]
"IEEE 802.1ag, Draft Standard for Connectivity Fault
Management", work in progress.
[IEEE-PBBTE]
"IEEE 802.1Qay Draft Standard for Provider Backbone
Bridging Traffic Engineering", work in progress.
[MPLS-TP-FWK]
"A Framework for MPLS in Transport Networks", Internet
Draft, work in progress.
[MPLS-TP-OAM-REQ]
"Requirements for OAM in MPLS Transport Networks",
Internet Draft, work in progress.
[RFC3469] "Framework for Multi-Protocol Label Switching (MPLS)-based
Recovery", RFC 3469, February 2003.
[RFC3471] "Generalized Multi-Protocol Label Switching (GMPLS)
Signaling Functional Description", RFC 3471, January 2003.
[RFC3473] "Generalized Multi-Protocol Label Switching (GMPLS)
Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC4377] "Operations and Management (OAM) Requirements for Multi-
Protocol Label Switched (MPLS) Networks", RFC 4377,
February 2006.
[RFC4420] "Encoding of Attributes for Multiprotocol Label Switching
(MPLS) Label Switched Path (LSP) Establishment Using
Resource ReserVation Protocol-Traffic Engineering
(RSVP-TE)", RFC 4420, February 2006.
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Authors' Addresses
Attila Takacs
Ericsson
Laborc u. 1.
Budapest, 1037
Hungary
Email: attila.takacs@ericsson.com
Don Fedyk
Nortel
600 Technology Park Drive
Billerica, MA 01821
USA
Email: dwfedyk@nortel.com
He Jia
Huawei
Email: hejia@huawei.com
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