One document matched: draft-takacs-ccamp-rsvp-te-eth-oam-ext-00.txt
Network Working Group A. Takacs
Internet-Draft B. Gero
Intended status: Experimental Ericsson
Expires: May 8, 2008 November 5, 2007
GMPLS RSVP-TE Ethernet OAM Extensions
draft-takacs-ccamp-rsvp-te-eth-oam-ext-00
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Abstract
The GMPLS controlled Ethernet Label Switching (GELS) work is
extending GMPLS RSVP-TE to support the establishment of Ethernet
LSPs. Ethernet Connectivity Fault Management (CFM) specifies an
adjunct OAM flow to check connectivity in Ethernet networks. CFM can
be also used with Ethernet LSPs for fault detection and triggering
recovery mechanisms. This memo proposes experimental extensions to
GMPLS RSVP-TE to support the setup of the associated CFM OAM entities
for point-to-point bidirectional Ethernet LSPs.
Note that the extensions defined may be applicable to other fault
detection mechanisms that use periodic Hello messages, e.g., BFD, as
well. Subsequent versions of the ID will consider the possibility of
general OAM extensions not limiting the applicability to Ethernet
OAM.
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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
1.1. Motivations and asumptions . . . . . . . . . . . . . . . . 4
1.2. Ethernet OAM operation overview . . . . . . . . . . . . . 5
1.3. Scope of the extension . . . . . . . . . . . . . . . . . . 7
2. GMPLS RSVP-TE Extensions . . . . . . . . . . . . . . . . . . . 8
2.1. Ethernet CFM TLV . . . . . . . . . . . . . . . . . . . . . 9
2.2. Monitoring Disabled - Admin_Status bit . . . . . . . . . . 10
2.3. Error handling . . . . . . . . . . . . . . . . . . . . . . 11
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 13
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Introduction
Ethernet Connectivity Fault Management (CFM) defines an adjunct
connectivity monitoring OAM flow to check the liveliness of Ethernet
networks [IEEE-CFM]. With Provider Backbone Bridging Traffic
Engineering (PBB-TE) [IEEE-PBBTE] Ethernet networks will 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) work is
extending the GMPLS control plane to support the establishment of
point-to-point PBB-TE data plane connections. We refer to GMPLS
established PBB-TE connections as Ethernet LSPs. GELS enables the
application of MPLS-TE and GMPLS provisioning and recovery features
in Ethernet networks.
MPLS OAM requirements are described in [RFC4377]. It provides
requirements to create consistent OAM functionality for MPLS
networks. The GMPLS OAM requirements are described in [GMPLS-OAM].
GMPLS OAM is based on the MPLS OAM requirements [RFC4377], in
addition it also considers the existing OAM techniques in non-packet
networks. This memo discusses the basic aspects of Ethernet OAM and
specifies RSVP-TE extensions addressing OAM requirements for Ethernet
networks.
1.1. Motivations and asumptions
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 memo and which
also motivated the extensions specified in this document.
1. 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.
2. In particular some LSPs may require automated ingress-LSR to
egress-LSR testing functionality, while others may not.
3. 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.
Generally, the frequency of OAM execution must be set properly, to
achieve the OAM requirements. When periodic messages are used for
liveliness check of LSPs the frequency of messages must be set
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properly fulfilling the requirements of the service and/or meeting
the detection time boundaries posed by possible congruent
connectivity check operations of higher layer applications.
Furthermore, 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.
In order for Ethernet LSPs to provide reliable service delivery, data
plane fault detection mechanisms are needed to trigger recovery
actions. Note that if lower layer fault detection (or protection)
mechanisms (such as those supported by SONET/SDH) are available, we
may rely on them and alleviate the need for frequent OAM message
exchanges for liveliness checks of Ethernet LSPs. However, when -
for example - Ethernet is deployed over a WDM optical layer that does
not provide the SONET/SDH protection characteristics, failure
detection and recovery must be solved in the Ethernet layer.
We assume that in networks where PBB-TE and GELS will be deployed the
default LSP path fault detection mechanism will be based on CFM
Connectivity Check Message (CCM) flows.
Fast fault detection and recovery are key to reliable service
delivery. However, there is a trade-off between fast fault detection
and signalling and processing overhead of connectivity monitoring
flows. Today, networks are providing transport of multiple service
types each with special requirements on quality of service including
the requirements on recovery. To balance the tradeoff between fast
detection and overhead it is essential that fault detection and
recovery are matching the requirements of the supported service, as
highlighted in [RFC3469]. For example, while business services may
require sub-second protection switching best effort Internet traffic
may rely on slower (in the order of seconds) restoration mechanisms.
These different requirements are reflected in the frequency of
connectivity monitoring packets that are needed to be exchanged over
the Ethernet LSP supporting a particular service type.
We assume that - for a network operator to be able to balance the
trade-off in fast failure detection and overhead - it will be
beneficial to configure the frequency of CCM messages on a per
Ethernet-LSP basis. Additionally, to simplify network management and
reduce the risk (and impact) of misconfiguration, it is desirable to
use Ethernet LSP signaling to configure CFM at both ends of the LSP.
1.2. Ethernet OAM operation overview
For the purposes of this document, we only discuss Ethernet OAM
[IEEE-CFM] aspects that are relevant for the connectivity monitoring
of bidirectional point-to-point PBB-TE connections. In the
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discussions we assume that the two directions of the bidirectional
PBB-TE connection use the same path to allow proper operation of the
Link Trace and Loopback Ethernet OAM functionality.
Note that the basic operation of CFM Connectivity Check is similar to
the operation of Bidirectional Forwarding Detection (BFD).
At both ends of the bidiretional point-to-point PBB-TE connection one
Maintenance Endpoint (MEP) is configured. Each MEP is provisioned
among others with its local VLAN ID (VID) and MAC address and the VID
and MAC address of the remote endpoint on witch the remote MEP is
configured. MEPs exchange Connectivity Check Messages (CCMs)
periodically with fixed intervals. Eight distinct intervals are
defined in [IEEE-CFM]:
+---+--------------------+-----------------+
| # | CCM Interval (CCI) | 3 bit reference |
+---+--------------------+-----------------+
| 0 | No CCMs | 000 |
| | | |
| 1 | 3 1/3 ms | 001 |
| | | |
| 2 | 10 ms | 010 |
| | | |
| 3 | 100 ms | 011 |
| | | |
| 4 | 1 s | 100 |
| | | |
| 5 | 10 s | 101 |
| | | |
| 6 | 1 min | 110 |
| | | |
| 7 | 10 min | 111 |
+---+--------------------+-----------------+
Table 1: CCM interval encoding
If 3 consecutive CCM messages are not received by one of the MEPs it
declares a connectivity failure and signals the failure in subsequent
CCM messages by setting the Remote Defect Indicator (RDI) bit. If a
MEP receives a CCM message with RDI set it immediately declares
failure. The detection of a failure may trigger protection switching
mechanisms or my be signalled to a management system. However, what
happens once a failure is detected is out of the scope of this
document.
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1.3. Scope of the extension
Although the setup of both unidirectional and bidirectional Ethernet
LSPs is feasible, due to the symmetric bidirectional connectivity
requirement of CFM, we only consider bidirectional point-to-point
Ethernet LSPs. The applicability for multipoint LSPs are for further
study.
The signalling of MEP identification parameters such as Maintenance
Association name (MA name) and MEP ID is left for further study.
Note that in addition to Connectivity Check, which is the focus of
this memo, CFM defines Link Trace and Loopback mechanisms as well.
The proposed extension automatically creates the MEPs and associates
them to the LSP. Once the MEPs are created the Link Trace and
Loopback functionality is available for on demand OAM actions.
Whether additional parameters besides those specified in the next
sections are required (or are beneficial) to support Link Trace
and/or Loopback is for further study. In addition parameters needed
to support measurement of Service Level Agreements (SLAs) is also
left for further study. Hence additional parameters may be defined
in subsequent versions of this document.
Note that the extensions defined may be applicable to other fault
detection mechanisms that use periodic Hello messages, e.g., BFD, as
well.
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2. GMPLS RSVP-TE Extensions
To simplify the configuration of connectivity monitoring, when an
Ethernet LSP is signalled the associated MEPs should be automatically
established. Further more, GMPLS signalling should be able to
enable/disable connectivity monitoring of a particular Ethernet LSP.
To configure MEPs some parameters must be provided to the Ethernet
OAM functions. First, the desired CCM interval must be specified by
the management system based on service requirements or operator
policy. Second, the MEPs must be aware of their own and the
reachability parameters of the remote MEP, in order CCM messages can
be sent and received. That is, when configuring a MEP, the CCM
interval, local MAC address and VID over which data plane traffic and
CCM messages are received, and the remote side MAC address and VID
with which data plane traffic and CCM messages are sent must be
known.
The Ethernet Label as defined in [Fedyk-GELS] consists of the
Destination MAC address (DA-MAC) and VID. Hence the necessary
reachability parameters for the MEPs can be obtained form Ethernet
Labels. Assuming the procedures described in [Fedyk-GELS] for
bidirectional Ethernet LSP establishment the MEP configuration should
be as follows. When the RSVP-TE signalling is initiated for the
bidirectional Ethernet LSP the local node creates the Upstream Label
from its MAC address and locally selected VID and generates the Path
message. Once the remote node receives the Path message it can use
the Upstream Label to extract the reachability information of the
initiator. Then it determines the MAC address and VID it would like
to use to receive traffic. These parameters determine the
reachability information of the local MEP. This in turn is used to
construct the Ethernet Label to be put into the Resv message. The
only information that is missing to setup the MEP, is the CCM
interval, which is signalled in a new TLV (the Ethernet CFM TLV) as
specified in this memo. Using this information the MEP can be
configured on the node. Once the Resv message successfully arrives
to the initiator it can extract the remote side reachability
information from the Ethernet Label whereby this node has also
obtained all the information needed to establish the MEP.
Once the MEPs are established the monitoring of the LSP is
operational. In certain situations, e.g., maintenance, re-
optimisation of LSPs, it is desirable to explicitly enable or disable
the monitoring of LSPs (i.e., start/stop exchanging CC messages). To
allow administrative control of LSP monitoring one bit in the
Admin_Status object is used. The "Monitoring Disabled" (M) bit is
allocated for this purpose.
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Note that since the reachability information could be extracted form
the Ethernet Labels it is an option not using any extension to
support MEP configuration of Ethernet LSPs. That is, an
implementation could use default parameters for CCM intervals to
setup connectivity monitoring. However, we rejected this approach,
as it does not provide means to set the CCM interval on a per LSP
level, leaving limited possibilities to configure CFM in a way that
matches the supported services' requirements. Moreover, there is no
way for providing additional CFM parameters to configure other
parameters of Ethernet OAM.
2.1. Ethernet CFM TLV
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.
Since the extensions defined for CFM Continuity Check are required to
be processed only by the edge nodes while internal nodes need to pass
on the information transparently, the LSP_ATTRIBUTES object should be
used for CFM related information signalling.
We propose a new TLV, the Ethernet CFM TLV (depicted below) for
supporting CFM CCM setup of Ethernet LSPs. This new TLV accommodates
information on CCM interval and also leaves room for further
extensions.
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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 (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CI | Reserved (set to all 0s) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
The type field indicates a new type: the Ethernet CFM TLV (2) (IANA
to define).
The length field is set to 4 bytes.
CI (4 bits): CCM Interval, using the 3 bit encoding shown in Table 1.
The first bit of the CI field is set to 0.
The Ethernet CFM TLV is carried in the LSP_ATTRIBUTE object and is
allowed in both the Path and Resv messages. The CCM interval field
in the Path message is the required value to be set for the remote
MEPs. The CCM interval field in the Resv message is optional and if
present it is the CCM interval that was set by the remote MEP. If
the Ethernet CFM TLV is not present in the Resv message this is
understood as the remote MEP would have been configured with the
requested CCM interval. The initiator upon receipt of the Resv
message can determine whether the egress set the same interval that
was requested or it used a different (slower) rate. If acceptable
the ingress may set the rate received in the Resv message otherwise
it initiates the tear down of the LSP. Note, both sides should use
the same CCM interval.
The negotiation allows accounting for the processing load posed on
nodes to process CCM messages. A node can consider the current CCM
load (determined by the number of active CCM flows and their
respective CCM intervals) when deciding to setup a new MEP with a
given CCM interval. It will be possible for a node to reject a small
CCM interval request (e.g., 3.3ms) and propose a new less frequent
rate for connectivity monitoring (e.g., 10ms).
2.2. 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].
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One bit is allocated for the administrative control of OAM
monitoring. In addition to the Reflect (R) bit, 7 bits are currently
occupied (assigned by IANA or temporarily in use by work in progress
Internet drafts). As the 8th bit (IANA to assign) this draft
introduces the Monitoring Disabled (M) bit. When this bit is set the
connectivity monitoring of the LSP is disabled.
2.3. Error handling
New error messages and procedures may be needed to handle failures of
OAM configuration. These will be described in subsequent versions of
this document.
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3. IANA Considerations
This document specifies a new TLV, the Ethernet CFM TLV, to be
carried in the LSP_ATTRIBUTES objects in Path and Resv messages.
One bit (Monitoring Disabled (M)) needs to be allocated in the
Administrative Status Object.
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4. 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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5. Acknowledgements
The authors would like to thank Adrian Farrel, Loa Andersson and Eric
Gray for their useful comments.
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6. References
[Fedyk-GELS]
"GMPLS control of Ethernet", 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.
[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
Balazs Gero
Ericsson
Laborc u. 1.
Budapest, 1037
Hungary
Email: balazs.gero@ericsson.com
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