PWE3 Working Group Dinesh Mohan (Ed.)
INTERNET-DRAFT Nortel Networks
Intended status: Standards Track
Expires: October 2012 Nabil Bitar (Ed.)
Verizon
Ali Sajassi (Ed.)
Cisco
April 12, 2012
MPLS and Ethernet OAM Interworking
draft-ietf-pwe3-mpls-eth-oam-iwk-05.txt
Abstract
This document specifies the mapping of defect states between
Ethernet Attachment Circuits (ACs) and associated Ethernet
Pseudowires (PWs) connected in accordance to the PWE3
architecture to realize an end-to-end emulated Ethernet service.
It standardizes the behavior of Provider Edges (PEs) with
respect to Ethernet PW and AC defects.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 12, 2012.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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.............................................. 2
1.1. Reference Model and Defect Locations................. 4
1.2. Abstract Defect States............................... 5
2. Terminology............................................... 7
3. PW Status and Defects..................................... 8
3.1. Use of Native Service (NS) notification.............. 8
3.2. Use of PW Status notification for MPLS PSNs.......... 9
3.3. Use of BFD Diagnostic Codes.......................... 9
4. Ethernet AC Defect States Entry or Exit Criteria......... 10
4.1. AC Receive Defect State Entry or Exit............... 10
4.2. AC Transmit Defect State Entry or Exit.............. 11
5. Ethernet AC and PW Defect States Interworking............ 12
5.1. PW Receive Defect Entry Procedures.................. 12
5.2. PW Receive Defect Exit Procedures................... 13
5.3. PW Transmit Defect Entry Procedures................. 14
5.4. PW Transmit Defect Exit Procedures.................. 15
5.5. AC Receive Defect Entry Procedures.................. 15
5.6. AC Receive Defect Exit Procedures................... 16
5.7. AC Transmit Defect Entry Procedures................. 16
5.8. AC Transmit Defect Exit Procedures.................. 17
6. Acknowledgments.......................................... 17
7. Security Considerations.................................. 17
8. IANA Considerations...................................... 17
9. References............................................... 17
9.1. Normative References................................ 17
9.2. Informative References.............................. 18
10. Appendix A: Ethernet Native Service Management.......... 18
1. Introduction
This document specifies the mapping of defect states between
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Ethernet Attachment Circuits (ACs) and associated Ethernet
Pseudowires (PWs) connected in accordance to the PWE3
architecture [RFC3985] to realize an end-to-end emulated
Ethernet service. This document augments the mapping of defect
states between a PW and associated AC of the end-to-end emulated
service in [RFC6310]. It covers the following Ethernet OAM
(Opertaions, Administration and Maintenance) mechanisms and
their interworking with PW OAM mechanisms:
- Ethernet Continuity Check (CC) [802.1ag][Y.1731]
- Ethernet Alarm Indication Signaling (AIS) and Remote Defect
Indication (RDI) [Y.1731]
- Ethernet Link OAM [802.3]
- Ethernet Local Management Interface {E-LMI} [MEF16]
Ethernet Link OAM [802.3] allows some Link defect states to be
detected and communicated across an Ethernet Link. When an
Ethernet AC is an Ethernet physical port, there may be some
application of Ethernet Link OAM [802.3]. Further, E-LMI [MEF16]
also allows for some Ethernet Virtual Circuit (EVC) defect
states to be communicated across an Ethernet UNI where Ethernet
UNI constitutes a single hop Ethernet Link (i.e. without any
802.1Q/.1ad compliant bridges in between). There may be some
application of E-LMI [MEF16] for failure notification across
single hop Ethernet AC in certain deployments that specifically
do not support [802.1ag] and/or [Y.1731]. [Y.1731] and [802.1ag]
based mechanisms are applicable in all types of Ethernet ACs.
Ethernet Link OAM [802.3] and E-LMI [MEF16] are optional and
their applicability is called out, where applicable.
Native Service (NS) OAM may be transported transparently over
the corresponding PW as user data. This is referred to as "the
single emulated OAM loop" mode per [RFC6310]. For Ethernet, as
an example, 802.1ag continuity check messages (CCMs) between two
Maintenance End Points (MEPs) can be transported transparently
as user data over the corresponding PW. At MEP locations,
service failure is detected when CCMs are not received over an
interval that is 3.5 times the local CCM transmission interval.
This is one of the failure conditions detected via CC.
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MEP peers can exist between Customer Equipment (CE) pairs (MEPs
of a given Maintenance Entity Group (MEG) reside on the CEs), PE
pairs (the MEPs of a given MEG reside on the PEs), or between
the CE and PE (the MEPs of a given MEG reside on the PE
and CE), as long as the MEG domain nesting rules are maintained.
It should be noted that Ethernet allows the definition of up to
8 MEG domains, each compromising of MEPs (down MEPs and UP MEPs)
and Maintenance Intermediate Points (MIPs). These domains can be
nested or touching. MEPs and MIPs generate and process messages
in the same domain level. Thus, whenever in this document we
refer to messages sent by a MEP or a MIP to a peer MEP or MIP,
these MEPs and MIPs are in the same MEG domain level.
When interworking two networking domains, such as native
Ethernet and PWs to provide an end-to-end emulated service,
there is need to identify the failure domain and location even
when a PE supports both the NS OAM mechanisms and the PW OAM
mechanisms. In addition, scalability constraints may not allow
running proactive monitoring, such as CCMs with transmission
enabled, at a PE to detect the failure of an EVC across the PW
domain. Thus, network-driven alarms generated upon failure
detection in the NS or PW domain and their mappings to the other
domain are needed. There are also cases where a PE may not be
able to process NS OAM messages received on the PW even when
such messages are defined, as in Ethernet case, necessitating
the need for fault notification message mapping between the PW
domain and the NS domain.
For Multi-Segment PWs (MS-PWs) [RFC5659], Switching PEs (S-PEs)
are not aware of the NS. Thus, failure detection and
notification at S-PEs will be based on PW OAM mechanisms.
Mapping between PW OAM and NS OAM will be required at the
Terminating PEs (T-PEs) to propagate the failure notification
to the EVC endpoints.
Similar to [RFC6310], the intent of this document is to
standardize the behavior of PEs with respect to failures on
Ethernet ACs and PWs, so that there is no ambiguity about the
alarms generated and consequent actions undertaken by PEs in
response to specific failure conditions.
1.1. Reference Model and Defect Locations
Figure 1 is the same as used in [RFC6310] and is reproduced
in this document as a reference to highlight defect locations.
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ACs PSN tunnel ACs
+----+ +----+
+----+ | PE1|==================| PE2| +----+
| |---(a)---(b)..(c)......PW1..(d)..(e)..(f)---(g)---| |
| CE1| (N1) | | | | (N2) |CE2 |
| |----------|............PW2.............|----------| |
+----+ | |==================| | +----+
^ +----+ +----+ ^
| Provider Edge 1 Provider Edge 2 |
| |
|<-------------- Emulated Service ---------------->|
Customer Customer
Edge 1 Edge 2
Figure 1: PWE3 Network Defect Locations
1.2. Abstract Defect States
Abstract Defect States are also introduced in [RFC6310]. This
document uses the same conventions, as shown in Figure 2 from
[RFC6310]. It may be noted however that CE devices, shown in
Figure 2, do not necessarily have to be end customer devices.
These are essentially devices in client network segments that
are connecting to the Packet Switched Network (PSN) for the
emuulated services.
+-----+
----AC receive ----->| |-----PW transmit---->
CE1 | PE1 |
PE2/CE2
<---AC transmit------| |<----PW receive-----
+-----+
(arrows indicate direction of user traffic impacted by a
defect)
Figure 2: Transmit and Receive Defect States and Notifications
PE1 may detect a receive defect in a local Ethernet AC via one
of the following mechanisms:
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- An AIS alarm generated at an upstream node in the client
domain (CE1 in Figure 2) and received by a local MEP.
- Failure of the local link on which the AC is configured.
Link failure may be detected via physical failures (e.g., loss
of signal (LoS)), via Ethernet Link OAM [802.3] critical link
event notifications generated at an upstream node CE1 with
"Dying Gasp" or "Critical Event" indication, or via a client
Signal Fail message [Y.1731].
- Failure to receive CCMs on the AC if a local MEP is
configured for the AC with CCM transmission enabled.
- A CCM from CE1 with interface status TLV indicating
interface down. Other CCM interface status TLVs will not be
used to indicate failure or recovery from failure.
It should be noted when a MEP at a PE or a CE receives a CCM
with the wrong MEG ID, MEP ID, or MEP level, the receving PE
or CE SHOULD treat such an event as an AC receive defect. In
any case, if such events persist for 3.5 times the MEP local
CCM transmission time, loss of continuity will be declared at
the receiving end.
An AC receive defect at PE1 impacts the ability of PE1 to
receive user traffic from the Client domain attached to PE1
via that AC.
PE1 may detect a receive defect in the PW via one of the
following mechanisms:
- A Forward Defect notification received from PE2. This defect
notification could point to problems associated with PE2's
inability to transmit traffic on the PW or PE2's inability to
receive traffic on its local AC from CE2.
- Unavailability of a PSN path in the PW domain to PE2.
A PW forward defect indication received on PE1 impacts the
ability of PE1 to receive traffic on the PW.
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PE1 may be notified of an AC transmit defect via one of the
following mechanisms:
- CCMs with RDI (Remote Defect Indication) bit set.
- In case when the AC is associated with a physical port,
failure of the local link on which the AC is configured (e.g.,
LOS or via Ethernet Link OAM [802.3] critical link event
notifications generated at an upstream node CE1 with "Link
Fault" indication).
An AC transmit defect impacts the ability of PE1 to send user
traffic on the local AC.
Similarly, PE1 may be notified of a PW transmit defect via
Reverse Defect indication from PE2, which could point to
problems associated with PE2's inability to receive traffic on
the PW or PE2's inability to transmit traffic on its local AC.
PW transmit defect impacts PE1 ability to send user traffic
toward CE2.
The procedures outlined in this document define the entry and
exit criteria for each of the four defect states with respect
to Ethernet ACs and corresponding PWs, and the consequent
actions that PE1 must support to properly interwork these
defect states and corresponding notification messages between
the PW domain and the Native Service (NS) domain. Receive
Defect state SHOULD have precedence over Transmit Defect state
in terms of handling, when both transmit and receive defect
states are identified simultaneously.
1.3. Specification of Requirements
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 [RFC2119].
2. Terminology
This document uses the following terms:
AIS Alarm Indication Signal
MD Level Maintenance Domain (MD) Level which identifies a value
in the range of 0-7 associated with Ethernet OAM frame.
MD Level identifies the span of the Ethernet OAM frame.
MEP Maintenance End Point is responsible for origination
and termination of OAM frames for a given MEG
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MIP Maintenance Intermediate Point is located between peer
MEPs and can process OAM frames but does not initiate
or terminate them
RDI Remote Defect Indication
Further, this document also uses the terminology and conventions
used in [RFC6310].
3. PW Status and Defects
[RFC6310] introduces a range of defects that impact PW
status. All these defect conditions are applicable for Ethernet
PWs.
Similarly, there are different mechanisms described in [RFC6310]
to detect PW defects, depending on the PSN type (e.g. MPLS PSN,
MPLS-IP PSN). Any of these mechanisms can be used when
monitoring the state of Ethernet PWs. [RFC6310] also discusses
the applicability of these failure detection mechanisms.
3.1. Use of Native Service (NS) notification
When a MEP is defined on the PE and associated with an Ethernet
PW,the PE can use native service OAM capabilities for failure
notifications. Options include:
- Sending of AIS frames from the local MEP to the MEP on the
remote PE when the MEP needs to convey PE receive defects, and
when CCM transmission is disabled.
- Suspension of CCM frames transmission from the local MEP to
the peer MEP on the remote PE to convey PE receive defects,
when CCM transmission is enabled.
- setting the RDI bit in transmitted CCM frames, when loss of
CCMs from the peer MEP is detected or the PE needs to convey PW
reverse defects.
These NS OAM notifications are inserted into the corresponding
PW.
Similarly, when the defect conditions are cleared, a PE can take
one of the following actions, depending on the mechanism that
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was used for failure notification, to clear the defect sate on
the peer PE:
- Stopping AIS frame transmission from the local MEP to the MEP
on the remote PE to clear PW receive defects.
- Resuming CCM frames transmission from the local MEP to the
peer MEP on the remote PE to clear PW forward defects
notification, when CCM transmission is enabled.
- Clearing the RDI bit in transmitted CCM frames, to clear PW
transmit defects notification, when CCM transmission is enabled.
3.2. Use of PW Status notification for MPLS PSNs
When PWs are established using LDP, LDP status notification
signaling MUST be used as the default mechanism to signal AC and
PW status and defects [RFC4447]. That is known as the "coupled
loop mode". For PWs established over an MPLS or MPLS-IP PSN
using other mechanisms (e.g. static configuration), inband
signaling using VCCV-BFD [RFC5885] SHOULD be used to convey AC
and PW status and defects.
[RFC6310] identifies the following PW defect status codepoints:
- Forward defect: corresponds to a logical OR of local AC
(ingress) Receive fault, local PSN-facing PW (egress) transmit
fault, and PW not forwarding fault.
- Reverse defect: corresponds to a logical OR of local AC
(egress) transmit fault and local PW PSN-facing (ingress)
receive fault.
There are also scenarios where a PE carries out PW label
withdrawal instead of PW status notification. These include
administrative disablement of the PW or loss of Target LDP
session with the peer PE.
3.3. Use of BFD Diagnostic Codes
When using VCCV, the control channel (CC) type and Connectivity
Verification (CV) Type are agreed on between the peer PEs using
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the OAM capability sub-TLV signaled as part of the interface
parameter TLV when using FEC 129 and the interface parameter
sub-TLV when using FEC 128.
As defined in [RFC6310], when CV type of 0x04 0r 0x1 is used to
indicate that BFD is used for PW fault detection only, PW defect
is detected via the BFD session while other defects, such as AC
defect or PE internal defects preventing it from forwarding
traffic, are communicated via LDP Status notification message in
MPLS and MPLS-IP PSNs or other mechanisms in L2TP-IP PSN.
Similarly, when CV type of 0x08 or 0x20 is used to indicate that
BFD is used for both PW fault detection and AC/PW Fault
Notification, all defects are signaled via BFD.
4. Ethernet AC Defect States Entry or Exit Criteria
4.1. AC Receive Defect State Entry or Exit
PE1 enters the AC Receive Defect state if any of the following
conditions is met:
- It detects or is notified of a physical layer fault on the
Ethernet interface. Ethernet link failure can be detected based
on loss of signal (LoS) or via Ethernet Link OAM [802.3]
critical link event notifications generated at an upstream node
CE1 with "Dying Gasp" or "Critical Event" indication.
- A MEP associated with the local AC receives an Ethernet AIS
frame.
- A MEP associated with the local AC does not receive CCM frames
from the peer MEP in the client domain (e.g. CE1) within an
interval equal to 3.5 times the CCM transmission period
configured for the MEP. This is the case when CCM transmission
is enabled.
- A CCM with interface status TLV indicating interface down.
Other CCM interface status TLVs will not be used to indicate
failure or recovery from failure.
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PE1 exits the AC Receive Defect state if all of the conditions
that resulted in entering the defect state are cleared. This
includes all of the following conditions:
- Any physical layer fault on the Ethernet interface, if
detected or notified previously is renoved (e.g., loss of signal
(LoS) cleared, or Ethernet Link OAM [802.3] critical link event
notifications with "Dying Gasp" or "Critical Event" indication
cleared at an upstream node CE1).
- A MEP associated with the local AC does not receive any
Ethernet AIS frame within a period indicated by previously
received AIS, if AIS resulted in entering the defect
state.
- A MEP associated with the local AC and configured with CCM
enabled receives a configured number (e.g., 3 or more) of
consecutive CCM frames from the peer MEP on CE1 within an
interval equal to a multiple (3.5) of the CCM transmission
period configured for the MEP.
- CCM indicates interface status up.
4.2. AC Transmit Defect State Entry or Exit
PE1 enters the AC Transmit Defect state if any of the following
conditions is met:
- It detects or is notified of a physical layer fault on the
Ethernet interface (e.g., via loss of signal (LoS) or Ethernet
Link OAM [802.3] critical link event notifications generated at
an upstream node CE1 with "Link Fault" indication).
- A MEP configured with CCM transmission enabled and associated
with the local AC receives a CCM frame, with its RDI bit set,
from the peer MEP in the client domain (e.g., CE1).
PE1 exits the AC Transmit Defect state if all of the conditions
that resulted in entering the defect state are cleared. This
includes all of the following conditions:
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- Any physical layer fault on the Ethernet interface, if
detected or notified previously is removed (e.g., LOS cleared,
Ethernet Link OAM [802.3] critical link event notifications
with "Link Fault" indication cleared at an upstream node CE1).
- A MEP configured with CCM transmission enabled and associated
with the local AC does not receive a CCM frame with RDI bit set,
having received a previous CCM frame with RDI bit set from the
peer MEP in the client domain (e.g. CE1).
5. Ethernet AC and PW Defect States Interworking
5.1. PW Receive Defect Entry Procedures
When the PW status on PE1 transitions from working to PW Receive
Defect state, PE1's ability to receive user traffic from CE2 is
impacted. As a result, PE1 needs to notify CE1 about this
problem.
Upon entry to the PW Receive Defect state, the following must be
done:
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is not enabled, the MEP associated with
the AC must transmit AIS frames periodically to the peer MEP in
the client domain (e.g., on CE1) based on configured AIS
transmission period.
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, and the MEP associated with
the AC is configured to support Interface Status TLV in CCM
messages, the MEP associated with the AC must transmit CCM
frames with Interface Status TLV as being down to the peer MEP
in the client domain (e.g., on CE1).
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, and the MEP
associated with the AC is configured to not support Interface
Status TLV in CCM messages, the MEP associated with the AC must
stop transmitting CCM frames to the peer MEP in the client
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domain (e.g., on CE1).
- If PE1 is configured to run E-LMI [MEF16] with CE1 and if
E-LMI is used for failure notification, PE1 must transmit E-LMI
asynchronous STATUS message with report type Single EVC
Asynchronous Status indicating that PW is Not Active.
Further, when PE1 enters the Receive Defect state, it must
assume that PE2 has no knowledge of the defect and must send
reverse defect failure notification to PE2. For MPLS PSN or
MPLS-IP PSN, this is done via either a PW Status notification
message indicating a reverse defect; or via VCCV-BFD diagnostic
code of reverse defect if VCCV CV type of 0x08 had been
negotiated. When Native Service OAM mechanism is supported on
PE1, it can also use the NS OAM notification as specified in
Section 3.1.
If PW receive defect is entered as a result of a forward defect
notification from PE2 or via loss of control adjacency, no
additional action is needed since PE2 is expected to be aware of
the defect.
5.2. PW Receive Defect Exit Procedures
When the PW status transitions from PW Receive Defect state to
working, PE1's ability to receive user traffic from CE2 is
restored. As a result, PE1 needs to cease defect notification to
CE1 by performing the following:
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is not enabled, the MEP associated with
the AC must stop transmitting AIS frames towards the peer MEP in
the client domain (e.g., on CE1).
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, and the MEP associated with
the AC is configured to support Interface Status TLV in CCM
messages, the MEP associated with the AC must transmit CCM
frames with Interface Status TLV as being Up to the peer MEP in
the client domain (e.g., on CE1).
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- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, and the MEP associated with
the AC is configured to not support Interface Status TLV in CCM
messages, the MEP associated with the AC must resume
transmitting CCM frames to the peer MEP in the client domain
(e.g., on CE1).
- If PE1 is configured to run E-LMI [MEF16] with CE1 and E-LMI
is used for fault notification, PE1 must transmit E-LMI
asynchronous STATUS message with report type Single EVC
Asynchronous Status indicating that PW is Active.
Further, if the PW receive defect was explicitly detected by
PE1, it must now notify PE2 about clearing of Receive Defect
state by clearing reverse defect notification. For PWs over
MPLS PSN or MPLS-IP PSN, this is either done via PW Status
message indicating working; or via VCCV-BFD diagnostic code if
VCCV CV type of 0x08/0x20 had been negotiated. When Native
Service OAM mechanism is supported on PE, it can also clear the
NS OAM notification specified in Section 3.1.
If PW receive defect was established via notification from PE2
or via loss of control adjacency, no additional action is
needed, since PE2 is expected to be aware of the defect
clearing.
5.3. PW Transmit Defect Entry Procedures
When the PW status transitions from working to PW Transmit
Defect state, PE1's ability to transmit user traffic to CE2 is
impacted. As a result, PE1 needs to notify CE1 about this
problem which has been detected by PE1.
Upon entry to the PW Transmit Defect state, the following must
be done:
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, the MEP associated with the
AC MUST set the RDI bit in transmitted CCM frames or send status
TLV with interface down to the peer MEP in the client domain
(e.g. on CE1).
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- If PE1 is configured to run E-LMI [MEF16] with CE1 and E-LMI
is used for fault notification, PE1 must transmit E-LMI
asynchronous STATUS message with report type Single EVC
Asynchronous Status indicating that PW is Not Active.
5.4. PW Transmit Defect Exit Procedures
When the PW status transitions from PW Transmit Defect state to
working, PE1's ability to transmit user traffic to CE2 is
restored. As a result, PE1 needs to cease defect notifications
to CE1 and perform the following:
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, the MEP associated with the
AC must clear the RDI bit in the transmitted CCM frames to the
peer MEP (e.g., on CE1).
- If PE1 is configured to run E-LMI [MEF16] with CE1, PE1 must
transmit E-LMI asynchronous STATUS message with report type
Single EVC Asynchronous Status indicating that PW is Active.
5.5. AC Receive Defect Entry Procedures
When AC status transitions from working to AC Receive Defect
state, PE1's ability to receive user traffic from CE1 is
impacted. As a result, PE1 needs to notify PE2 and CE1 about
this problem.
If the AC receive defect is detected by PE1, it must notify PE2
in the form of a forward defect notification.
When NS OAM is not supported on PE1, and for PW over MPLS PSN
or MPLS-IP PSN, forward defect notification is done via either
PW Status message indicating a forward defect or via VCCV-BFD
diagnostic code of forward defect if VCCV CV type of 0x08/0x20
had been negotiated.
When Native Service OAM mechanism is supported on PE1, it can
also use the NS OAM notification as specified in Section 3.1.
In addition to above actions, PE1 must perform the following:
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- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, the MEP associated with the
AC must set the RDI bit in transmitted CCM frames.
5.6. AC Receive Defect Exit Procedures
When AC status transitions from AC Receive Defect to working,
PE1's ability to receive user traffic from CE1 is restored. As
a result, PE1 needs to cease defect notifications to PE2 and CE1
and perform the following:
- When NS OAM is not supported on PE1 and for PW over MPLS PSN
or MPLS-IP PSN, forward defect notification is cleared via PW
Status message indicating a working state; or via VCCV-BFD
diagnostic code if VCCV CV type of 0x08 or 0x20 had been
negotiated.
- When Native Service OAM mechanism is supported on PE1, PE1
clears the NS OAM notification as specified in Section 3.1.
- If PE1 is configured with a down MEP associated with the local
AC and CCM transmission is enabled, the MEP associated with the
AC must clear the RDI bit in transmitted CCM frames to the
peer MEP in the client domain (e.g., on CE1).
5.7. AC Transmit Defect Entry Procedures
When AC status transitions from working to AC Transmit Defect,
PE1's ability to transmit user traffic to CE1 is impacted. As a
result, PE1 needs to notify PE2 about this problem.
If the AC transmit defect is detected by PE1, it must notify PE2
in the form of a reverse defect notification.
When NS OAM is not supported on PE1, in PW over MPLS PSN or
MPLS-IP PSN, reverse defect notification is either done via PW
Status message indicating a reverse defect; or via VCCV-BFD
diagnostic code of reverse defect if VCCV CV type of 0x08 or
0x20 had been negotiated.
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When Native Service OAM mechanism is supported on PE1, it can
also use the NS OAM notification as specified in Section 3.1.
5.8. AC Transmit Defect Exit Procedures
When AC status transitions from AC Transmit defect to working,
PE1's ability to transmit user traffic to CE1 is restored. As a
result, PE1 must clear reverse defect notification to PE2.
When NS OAM is not supported on PE1 and for PW over MPLS PSN or
MPLS-IP PSN, reverse defect notification is cleared via either a
PW Status message indicating a working state or via VCCV-BFD
diagnostic code if VCCV CV type of 0x08 had been negotiated.
When Native Service OAM mechanism is supported on PE1, PE1 can
clear NS OAM notification as specified in Section 3.1.
6. Acknowledgments
The authors are thankful to Samer Salam for his valuable
comments.
7. Security Considerations
This document does not impose any security concerns since it
makes use of existing OAM mechanisms and mapping of these
messages does not change inherent security features.
8. IANA Considerations
This document has no actions for IANA.
9. References
9.1. Normative References
[Y.1731] "OAM Functions and mechanisms for Ethernet based
networks", ITU-T Y.1731, May 2006
[802.1ag] "Connectivity Fault Management", IEEE 802.1ag/D8.1,
July 2007
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4447] "Pseudowire Setup and Maintenance using LDP", RFC4447,
April 2006
[RFC5885] "Bidirectional Forwarding Detection (BFD) for the
Pseudowire Virtual Circuit Connectivity Verification (VCCV)",
RFC5885, June 2010
[802.3] "CDMA/CD access method and physical layer
specifications", Clause 57 for Operations, Administration and
Maintenance, 2005
[MEF16] "Ethernet Local Management Interface", MEF16, January
2006
9.2. Informative References
[RFC3985] "Pseudo Wire Emulation Edge-to-Edge (PWE3)
Architecture", RFC 3985, April 2005
[RFC6310] "Pseudo Wire (PW) OAM Message Mapping", draft-ietf-
pwe3-oam-msg-map-14.txt, Work in progress, October 2010
[RFC5659] "An Architecture for Multi-Segment Pseudo Wire
Emulation Edge-to-Edge", RFC5659, October 2009
10. Appendix A: Ethernet Native Service Management
Ethernet OAM mechanisms are broadly classified into two
categories: Fault Management (FM) and Performance Monitoring
(PM). ITU-T Y.1731 provides coverage for both FM and PM while
IEEE 802.1ag provides coverage for a sub-set of FM functions.
Ethernet OAM also introduces the concept of Maintenance Entity
(ME) which is used to identify the entity that needs to be
managed. An ME is inherently a point-to-point association.
However, in case of a multipoint association, Maintenance Entity
Group (MEG) consisting of different MEs is used. IEEE 802.1 uses
the concept of Maintenance Association (MA) which is used to
identify both point-to-point and multipoint associations. Each
MA consists of Maintenance End Points (MEPs) which are
responsible for originating OAM frames. In between the MEPs,
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there can also be Maintenance Intermediate Points (MIPs) which
do not originate OAM frames however do respond to OAM frames
from MEPs.
Ethernet OAM allows for hierarchical maintenance entities to
allow for simultaneous end-to-end and segment monitoring. This
is achieved by having a provision of up to 8 Maintenance Domain
Levels (MD Levels) where each MEP or MIP is associated with a
specific MD Level.
It is important to note that the common set of FM mechanisms
between IEEE 802.1ag and ITU-T Y.1731 are completely compatible.
The common FM mechanisms include:
1) Continuity Check Messages (CCM)
2) Loopback Message (LBM) and Loopback Reply (LBR)
3) Linktrace Message (LTM) and Linktrace Reply (LTR)
CCM messages are used for fault detection including misconnections
and mis-configurations. Typically CCM messages are sent as
multicast frames or Unicast frames and also allow RDI
notifications. LBM/LBR are used to perform fault verification,
while also allow for MTU verification and CIR/EIR measurements.
LTM/LTR can be used for discovering the path traversed between a
MEP and another target MIP/MEP in the same MA. LTM/LTR also allow
for fault localization.
In addition, ITU-T Y.1731 also specifies the following FM
functions:
4) Alarm Indication Signal (AIS)
AIS allows for fault notification to downstream and upstream nodes
Further, ITU-T Y.1731 also specifies the following PM functions:
5) Loss Measurement Message (LMM) and Reply (LMR)
6) Delay Measurement Message (DMR) and Reply (DMR)
7) 1-way Delay Message (1DM)
While LMM/LMR is used to measure Frame Loss Ratio (FLR), DMM/DMR is
used to measure single-ended (aka two-way) Frame Delay (FD) and
Frame Delay Variation (FDV, also known as Jitter). 1DM can be used
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for dual-ended (aka one-way) FD and FDV measurements.
Authors' Addresses:
Dinesh Mohan
Nortel
3500 Carling Ave
Ottawa, ON K2H8E9
Email: dinmohan@hotmail.com
Nabil Bitar
Verizon
60 Sylvan Road
Waltham, MA 02145
Email: nabil.n.bitar@verizon.com
Simon Delord
Telstra
242 Exhibition St
Melbourne VIC 3000, Australia
E-mail: simon.a.delord@team.telstra.com
Philippe Niger
France Telecom
2 av. Pierre Marzin
22300 LANNION, France
E-mail: philippe.niger@francetelecom.com
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
Ray Qiu
330 Central Expressway
Santa Clara, CA 95050, US
Email: ray@huawei.com
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