PWE3 Working Group Dinesh Mohan (Ed.)
INTERNET-DRAFT Nortel Networks
Intended status: Standards Track
Expires: January 2014 Nabil Bitar (Ed.)
Verizon
Ali Sajassi (Ed.)
Cisco
Simon Delord
Alcatel-Lucent
Philipe Niger
France Telecom
Ray Qiu
Juniper
July 15, 2013
MPLS and Ethernet OAM Interworking
draft-ietf-pwe3-mpls-eth-oam-iwk-08.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/.
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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 January 14, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction............................................. 3
1.1. Specification of Requirements....................... 3
2. Overview................................................. 3
2.1. Reference Model and Defect Locations................ 5
2.2. Abstract Defect States.............................. 5
3. Abbreviations and Terminology............................ 7
3.1. Abbreviations....................................... 7
3.2. Terminology......................................... 7
4. PW Status and Defects.................................... 8
4.1. Use of Native Service (NS) Notification............. 8
4.2. Use of PW Status Notification for MPLS PSNs......... 9
4.3. Use of BFD Diagnostic Codes......................... 9
4.4. PW Defect States Entry and Exit Criteria........... 10
4.4.1. PW Receive Defect State Entry and Exit........ 10
4.4.2. PW Transmit Defect State Entry and Exit....... 10
5. Ethernet AC Defect States Entry and Exit Criteria11..... 11
5.1. AC Receive Defect State Entry and Exit............. 11
5.2. AC Transmit Defect State Entry and Exit............ 12
6. Ethernet AC and PW Defect States Interworking........... 12
6.1. PW Receive Defect Entry Procedures................. 12
6.2. PW Receive Defect Exit Procedures.................. 13
6.3. PW Transmit Defect Entry Procedures................ 14
6.4. PW Transmit Defect Exit Procedures................. 15
6.5. AC Receive Defect Entry Procedures................. 15
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6.6. AC Receive Defect Exit Procedures.................. 16
6.7. AC Transmit Defect Entry Procedures................ 16
6.8. AC Transmit Defect Exit Procedures................. 16
7. Security Considerations................................. 17
8. IANA Considerations..................................... 17
9. Acknowledgments......................................... 17
10. References............................................. 17
10.1. Normative References...............................17
10.2. Informative References.............................18
11. Appendix A: Ethernet Native Service Management......... 19
1. Introduction
RFC 6310 [RFC6310] specifies the mapping and notification of defect
states between a pseudowire (PW) and the Attachment Circuit (AC) of
the end-to-end emulated service. It standardizes the behavior of
Provider Edges (PEs) with respect to PW and AC defects for a number
of technologies (e.g., Asynchronous Transfer Mode (ATM), Frame
Relay (FR)) emulated over PWs in MPLS and MPLS/IP Packet Switched
Networks (PSNs). However, RFC 6310 does not describe this function
for the Ethernet PW service owing to its unique characteristics.
This document specifies the mapping of defect states between ACs
and associated Ethernet 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 RFC 6310. Similar to RFC 6310, 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. 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. Overview
There are a number of Operations, Administration and Maintenance
(OAM) technologies defined for Ethernet, providing various
functionalities. This document covers the following Ethernet OAM
mechanisms and their interworking with PW OAM mechanisms:
- Ethernet Link OAM [802.3]
- Ethernet Local Management Interface {E-LMI} [MEF16]
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- 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] 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 User Network Interface (UNI) where
Ethernet UNI constitutes a single hop Ethernet Link (i.e., without
any IEEE 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 IEEE 802.1ag [802.1ag] and/or ITU-T Y.1731 [Y.1731],
simply referred to as 802.1ag and Y.1731, respectively, in this
document. Y.1731 and 802.1ag based mechanisms are applicable in all
types of Ethernet ACs. Ethernet Link OAM and E-LMI 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
Group 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 continuity check. 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 level nesting rules are maintained. It should be noted that
Ethernet allows the definition of up to 8 MEG levels, each
compromising of MEPs (Down MEPs and Up MEPs) and Maintenance Group
Intermediate Points (MIPs). These levels can be nested or touching.
MEPs and MIPs generate and process messages in the same MEG 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 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
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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.
2.1. 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.
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
2.2. 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 emulated services.
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+-----+
----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
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.
Following is a summary of the defect states from the viewpoint of
PE1 in Figure 2:
- A PW receive defect at PE1 impacts PE1 ability to receive traffic
on the PW. PW defect state entry and exit criteria are described in
section 4.4.1.
- A PW transmit defect at PE1 impacts PE1 ability to send user
traffic toward CE2. 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
state defect entry and exit criteria are described in section
4.4.2.
- An AC receive defect at PE1 impacts PE1 ability to receive user
traffic from the Client domain attached to PE1 via that AC. AC
receive state entry and exit criteria are described in section 5.1
- An AC transmit defect at PE1 impacts PE1 ability to send user
traffic on the local AC. AC transmit defect state entry and exit
criteria are described in section 5.2.
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3. Abbreviations and Terminology
3.1. Abbreviations
AIS Alarm Indication Signal
AC Attachment Circuit
BFD Bidirectional Forwarding Detection
CC Continuity Check
CCM Continuity Check Message
CE Customer Equipment
CV Connectivity Verification
E-LMI Ethernet Local Management Interface
EVC Ethernet Virtual Circuit
LDP Label Distribution Protocol
LoS Loss of Signal
MA Maintenance Association
MD Maintenance Domain
ME Maintenance Entity
MEG Maintenance Entity Group
MEP MEG End Point
MIP MEG Intermediate Point
MPLS Multiprotocol Label Switching
MS-PW Multi-Segment Pseudowire
NS Native Service
OAM Operations, Administration, and Maintenance
PE Provider Edge
PSN Packet Switched Network
PW Pseudowire
RDI means Remote Defect Indication when used in the context of
CCM
RDI Reverse Defect Indication when used to semantically refer
to defect indication in the reverse direction
S-PE Switching Provider Edge
TLV Type Length Value
T-PE Terminating Provider Edge
3.2. Terminology
This document uses the following terms with corresponding
definitions:
- MEG Level: identifies a value in the range of 0-7 associated
with Ethernet OAM frame. MEG Level identifies the span of the
Ethernet OAM frame.
- MEP: MEG End Point is responsible for origination and
termination of OAM frames for a given MEG.
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- MIP: MEG Intermediate Point is located between peer
MEPs and can process OAM frames but does not initiate them.
- MPLS PSN: A PSN that makes use of MPLS label Switched Paths
[RFC3031] as the tunneling technology to forward PW packets.
-MPLS/IP PSN: A PSN that makes use of MPLS-in-IP tunneling
[RFC4023] to tunnel MPLS-labeled PW packets over IP tunnels.
Further, this document also uses the terminology and conventions
used in [RFC6310].
4. 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.
4.1. Use of Native Service (NS) Notification
When two PEs terminate am Ethernet PW with associated MEPs, each PE
can use native service (NS) OAM capabilities for failure
notifications by transmitting appropriate NS OAM messages over the
corresponding PW to the remote PE. 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.
Similarly, when the defect conditions are cleared, a PE can take
one of the following actions, depending on the mechanism that 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.
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- 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.
4.2. Use of PW Status Notification for MPLS PSNs
RFC 4447 [RFC4447] specifies that for PWs that have been set up
using the Label Distribution Protocol (LDP), the default mechanism
to signal status and defects for ACs and PWs is the LDP Status
Notification message. 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.
Alternatively, the mechanisms defined in [RFC6478] MAY be used.
[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.
4.3. 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 the
VCC parameter field signaled as a sub-TLV of the interface
parameters TLV when using FEC 129 and the interface parameter sub-
TLV when using FEC 128 [RFC5085].
As defined in [RFC6310], when CV type of 0x04 or 0x10 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.
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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.
4.4. PW Defect States Entry and Exit Criteria
4.4.1. PW Receive Defect State Entry and Exit
As described in [RFC6310] section 6.2.1, PE1 will enter the PW
receive defect state if one or more of the following occurs:
- It receives a forward defect indication (FDI) from PE2
indicating either a receive defect on the remote AC or that PE2
detected or was notified of downstream PW fault.
- It detects loss of connectivity on the PSN tunnel upstream of
PE1, which affects the traffic it receives from PE2.
- It detects a loss of PW connectivity through VCCV-BFD, VCCV-
PING, or NS OAM mechanisms (i.e., CC) when enabled, which affects
the traffic it receives from PE2.
Note that if the PW LDP control session between the PEs fails, the
PW is torn down and needs to be re-established. However, the
consequent actions towards the ACs are the same as if the PW
entered the receive defect state.
PE1 will exit the PW receive defect state when the following
conditions are met. Note that this may result in a transition to
the PW operational state or the PW transmit defect state.
- All previously detected defects have disappeared
- PE2 cleared the FDI, if applicable
4.4.2. PW Transmit Defect State Entry and Exit
PE1 will enter the PW transmit defect state if the following
conditions occur:
- It receives a Reverse Defect Indication (RDI) from PE2
indicating either a transmit fault on the remote AC or that PE2
detected or was notified of an upstream PW fault.
- It is not already in the PW receive defect state.
PE1 will exit the transmit defect state if it receives an OAM
message from PE2 clearing the RDI, or it has entered the PW
receive defect state.
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5. Ethernet AC Defect States Entry and Exit Criteria
5.1. AC Receive Defect State Entry and 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, or via a client Signal Fail
message [Y.1731].
- A MEP associated with the local AC receives an Ethernet AIS frame
from CE1.
- 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.
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 receiving 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.
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 removed (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
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equal to a multiple (3.5) of the CCM transmission period configured
for the MEP.
- CCM indicates interface status up.
5.2. AC Transmit Defect State Entry and 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 where the AC is configured (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 (Remote Defect
Indication) 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:
- 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).
6. Ethernet AC and PW Defect States Interworking
6.1. 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
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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 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 or 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 4.1.
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.
6.2. 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
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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).
- 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 as
specified in Section 4.1.
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.
6.3. 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).
- 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.
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- If the PW failure was detected by PE1 without receiving reverse
defect notification from PE2, PE1 MUST assume PE2 has no knowledge
of the defect and MUST notify PE2 by sending FDI."
6.4. 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 or send status TLV with interface up to the peer MEP in the
client domain (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.
- PE1 MUST clear the FDI to PE2, if applicable.
6.5. 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 4.1.
In addition to the 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.
6.6. 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 4.1.
- 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).
6.7. 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.
When Native Service OAM mechanism is supported on PE1, it can also
use the NS OAM notification as specified in Section 4.1.
6.8. 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.
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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 or 0x20 had been
negotiated.
When Native Service OAM mechanism is supported on PE1, PE1 can
clear NS OAM notification as specified in Section 4.1.
7. Security Considerations
The OAM interworking mechanisms described in this document do not
change the security functions inherent in the actual messages. All
generic security considerations applicable to PW traffic specified
in Section 10 of [RFC3985] are applicable to NS OAM messages
transferred inside the PW.
Security considerations in Section 10 of [RFC5085] for VCCV apply
to the OAM messages thus transferred. Security considerations
applicable to the PWE3 control protocol of [RFC4447] Section 8.2
apply to OAM indications transferred using the LDP status message.
Since the mechanisms of this document enable propagation of OAM
messages and fault conditions between native service networks and
PSNs, continuity of the end-to-end service depends on a trust
relationship between the operators of these networks. Security
considerations for such scenarios are discussed in Section 7 of
[RFC5254].
8. IANA Considerations
This document has no actions for IANA.
9. Acknowledgments
The authors are thankful to Samer Salam, Matthew Bocci, Yaakov
Stein, David Black, Lizhong Jin, Greg Mirsky, Huub van Helvoort,
and Adrian Farrel for their valuable input and comments.
10. References
10.1. Normative References
[RFC6310] "Pseudowire (PW) Operations, Administration, and
Maintenance (OAM) Message Mapping", RFC 6310, July 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[802.3] "CDMA/CD access method and physical layer specifications",
Clause 57 for Operations, Administration and Maintenance, 2005.
[MEF16] "Ethernet Local Management Interface", Metro Ethernet Forum
Technical Specification MEF16, January 2006.
[802.1ag] "Connectivity Fault Management", IEEE 802.1ag, December
2007.
[Y.1731] "OAM Functions and mechanisms for Ethernet based
networks", ITU-T Y.1731, May 2006.
[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.
[RFC6478] Martini, L., Swallow, G., Heron, G., and Bocci, M.,
"Pseudowire Status for Static Pseudowires", RFC 6478, May 2012.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual
Circuit Connectivity Verification (VCCV): A Control
Channel for Pseudowires", RFC 5085, December 2007.
10.2. Informative References
[RFC3985] "Pseudo Wire Emulation Edge-to-Edge(PWE3) Architecture",
RFC 3985, April 2005.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon,"Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
RFC4023] Worster, T., Rekhter, Y., and E. Rosen"Encapsulating MPLS
in IP or Generic Routing Encapsulation (GRE)", RFC 4023, March
2005.
[RFC5659] "An Architecture for Multi-Segment Pseudo Wire Emulation
Edge-to-Edge", RFC5659, October 2009.
[RFC5254] Bitar, N., Bocci, M., and L. Martini, "Requirements for
Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)", RFC 5254,
October 2008.
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11. 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 MEG/MA consists of MEG
End Points (MEPs) which are responsible for originating OAM frames.
In between the MEPs, there can also be MEG 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 MEG Levels (MD Levels)
where each MEP or MIP is associated with a specific MEG 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 MEG. LTM/LTR also allow
for fault localization.
In addition, ITU-T Y.1731 also specifies the following FM
functions:
4) Alarm Indication Signal (AIS)
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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 (DMN) 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
for dual-ended (aka one-way) FD and FDV measurements.
Authors' Addresses
Dinesh Mohan
Nortel
Email: dinmohan@hotmail.com
Nabil Bitar
Verizon
60 Sylvan Road
Waltham, MA 02145
Email: nabil.n.bitar@verizon.com
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
Simon Delord
Alcatel-Lucent
215 Spring Street
Melbourne, Australia
E-mail: simon.delord@gmail.com
Philippe Niger
France Telecom
2 av. Pierre Marzin
22300 LANNION, France
E-mail: philippe.niger@francetelecom.com
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Ray Qiu
Juniper
1194 North Mathilda Avenue
Sunnyvale, CA 94089, US
Email: rqiu@juniper.net
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