Network Working Group Mustapha Aissaoui
Internet Draft Peter Busschbach
Expires: July 6, 2012 Alcatel-Lucent
Dave Allan
Ericsson
Monique Morrow
Cisco Systems Inc.
Thomas Nadeau
CA Technologies
Editors
January 6, 2012
OAM Procedures for VPWS Interworking
draft-ietf-l2vpn-vpws-iw-oam-03.txt
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Abstract
This draft proposes OAM procedures for the Ethernet interworking, IP
interworking and FR-ATM interworking Virtual Private
Wire Service (VPWS).
Conventions used in this document
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 RFC-2119.
Table of Contents
1. Contributors...................................................3
2. Introduction...................................................3
3. Conventions....................................................4
4. Reference Model and Defect Locations...........................5
5. Abstract Defect States.........................................6
6. VPWS OAM Modes.................................................8
7. PW Defect State Entry/Exit.....................................9
8. ATM AC Defect State Entry/Exit................................10
9. FR AC Defect State Entry/Exit.................................10
10. Ethernet AC Defect State Entry/Exit..........................10
11. Security Considerations......................................10
12. IANA Considerations..........................................11
13. References...................................................11
13.1. Normative References....................................11
13.2. Informative References..................................11
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14. Editor's Addresses...........................................12
1. Contributors
The following individuals contributed significant ideas or text:
Matthew Bocci, matthew.bocci@alcatel-lucent.com
Simon Delord, simon.delord@gmail.com
Paul Doolan, paul.doolan@nsn.com
Mike Loomis, mike.loomis@alcatel-lucent.com
Hamid Ould-Brahim, hbrahim@nortel.com
Vasile Radoaca, vasile.radoaca@alcatel-lucent.com
Himanshu Shah, hshah@force10networks.com
David Watkinson, david.watkinson@alcatel-lucent.com
John Z. Yu.
2. Introduction
This draft augments OAM message mapping [OAM-MSG] with OAM
procedures for scenarios when the attachment circuit does not
correspond to the pseudo wire. When combined with procedures defined
in [OAM-MSG], comprehensive OAM interworking can be defined for VPWS
services. VPWS services are defined in the L2 VPN framework [L2VPN-
FRMK].
The following VPWS types are covered in this document:
1. VPWS with heterogeneous ACs of ATM and FR types, and in which the
PW type is ATM or FR. In this case, FR-ATM service interworking
[FRF8.2] is performed in PE1 (or PE2) and a FR (or ATM) PW is
extended to the remote PE. This VPWS type will be referred to as
''FR-ATM Interworking VPWS''.
2. VPWS with heterogeneous ACs of ATM, FR, and Ethernet types, and
in which the PW type is Ethernet. This VPWS type will be referred
to as ''Ethernet Interworking VPWS''.
3. VPWS with heterogeneous ACs of ATM, FR, and Ethernet types, and
in which the PW type is IP [ARP-Mediation]. This VPWS type will
be referred to as ''IP Interworking VPWS''.
OAM procedures for homogeneous VPWS circuits of ATM, FR, or Ethernet
types are described in [OAM-MSG].
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3. Conventions
The words "defect" and "fault" are used interchangeably to mean any
condition that obstructs forwarding of user traffic between the CE
endpoints of the PW service.
The words "defect notification" and "defect indication" are used
interchangeably to mean any OAM message generated by a PE and sent
to other nodes in the network to convey the defect state local to
this PE.
An end-to-end virtual circuit in a VPWS consists of a 3 segment set:
<AC, PW, AC> [L2VPN-FRMK]. Note that the AC does not need to connect
a CE directly to a PE. An intermediate L2 network may exist.
A VPWS is homogeneous if AC and PW types are the same. E.g., ATM
VPWS: <ATM AC, ATM PW, ATM AC>.
A VPWS is heterogeneous if any two segments of the circuit are of
different types. E.g., IP interworking circuit: <ATM AC, IP PW, ATM
AC>, or <ATM AC, IP PW, ETH AC>.
The PW of a VPWS can be carried over three types of Packet Switched
Networks (PSNs). An "MPLS PSN" makes use of MPLS Label Switched
Paths [RFC3031] as the tunneling technology to forward the PW
packets. An "MPLS/IP PSN" makes use of MPLS-in-IP tunneling
[RFC4023], with an MPLS shim header used as PW demultiplexer. An
"L2TPv3/IP PSN" makes use of L2TPv3/IP [RFC3931] as the tunneling
technology with the L2TPv3/IP Session ID as the PW demultiplexer.
If LSP-Ping [RFC4379] is run over a PW as described in [RFC5085], it
will be referred to as "VCCV-Ping". If BFD is run over a PW as
described in [RFC5885], it will be referred to as "VCCV-BFD".
While PWs are inherently bidirectional entities, defects and OAM
messaging are related to a specific traffic direction. We use the
terms "upstream" and "downstream" to identify PEs in relation to the
traffic direction. A PE is upstream for the traffic it is forwarding
and is downstream for the traffic it is receiving.
We use the terms "local" and "remote" to identify native service
networks and ACs in relation to a specific PE. The local AC is
attached to the PE in question, while the remote AC is attached to
the PE at the other end of the PW.
A "transmit defect" is any defect that impacts traffic that is meant
to be sent or relayed by the observing PE. A "receive defect" is any
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defect that impacts traffic that is meant to be received by the
observing PE. Note that a receive defect also impacts traffic meant
to be relayed, and thus can be considered to incorporate two defect
states. Thus when a PE enters both receive and transmit defect
states of a PW service, the receive defect takes precedence over the
transmit defect in terms of the consequent actions.
A "forward defect indication" (FDI) is sent in the same direction as
the user traffic impacted by the defect. A "reverse defect
indication" (RDI) is sent in the direction opposite to that of the
impacted traffic.
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].
4. Reference Model and Defect Locations
Figure 1 illustrates the VPWS network reference model with an
indication of the possible defect locations. This model will be
referenced in the remainder of this document for describing the OAM
procedures.
ACs PSN tunnel ACs
+----+ +----+
+----+ | PE1|==================| PE2| +----+
| |---(a)---(b)..(c)......PW1..(d)..(c)..(f)---(e)---| |
| 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
The procedures will be described in this document from the viewpoint
of PE1, so that N1 is the local native service network and N2 is the
remote native service network. It is assumed that the AC and PW are
of different types at PE1. PE2 will typically implement the same
procedures but it can use an AC and PW of the same or different
types. Note that PE1 is the upstream PE for traffic originating in
the local NS network N1, while it is the downstream PE for traffic
originating in the remote NS network N2.
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The following is a brief description of the defect locations:
a. Defect in NS network N1. This covers any defect in network N1
that impacts all or some ACs attached to PE1, and is thus a
local AC defect. The defect is conveyed to PE1 and to NS
network N2 using NS specific OAM defect indications.
b. Defect on a PE1 AC interface (another local AC defect).
c. Defect on a PE1 PSN interface.
d. Defect in the PSN network. This covers any defect in the PSN
that impacts all or some PWs between PE1 and PE2. The defect is
conveyed to the PE using a PSN and/or a PW specific OAM defect
indication. Note that both data plane defects and control plane
defects must be taken into consideration. Although control
messages may follow a different path than PW data plane
traffic, a control plane defect may affect the PW status.
e. Defect in NS network N2 (another remote AC defect). This covers
any defect in N2 which impacts all or a subset of ACs attached
to PE2. The defect is conveyed to PE2 and to NS network N1
using the NS OAM defect indication.
f. Defect on a PE2 AC interface (a remote AC defect).
5. Abstract Defect States
sss PE1 must track four defect states that reflect the observed
states of both directions of the PW service on both the AC and the
PW sides.
Defects may impact one or both directions of the PW service. The
observed state is a combination of defects directly detected by PE1
and defects of which it has been made aware via notifications.
+-----+
----AC receive---->| |-----PW transmit---->
CE1 PE1 | PE2/CE2
<---AC transmit----| |<----PW receive-----
+-----+
(arrows indicate direction of user traffic impacted by a defect)
Figure 2: Receive and Transmit Defect States
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PE1 will directly detect or be notified of AC receive or PW receive
defects as they occur upstream of PE1 and impact traffic being sent
to PE1. As a result, PE1 enters the AC or PW receive defect state.
In Figure 2, PE1 may be notified of a receive defect in the AC by
receiving a Forward Defect indication, e.g., ATM AIS, from CE1 or an
intervening network. This defect notification indicates that user
traffic sent by CE1 may not be received by PE1 due to a defect. PE1
can also directly detect an AC receive defect if it resulted from a
failure of the receive side in the local port or link over which the
AC is configured.
Similarly, PE1 may detect or be notified of a receive defect in the
PW by receiving a Forward Defect indication from PE2. If PW status
is used for fault notification, this message will indicate a Local
PSN-facing PW (egress) Transmit Fault or a Local AC (ingress)
Receive Fault at PE2. This defect notification indicates that user
traffic sent by CE2 may not be received by PE1 due to a defect. As a
result, PE1 enters the PW receive defect state.
Note that a Forward Defect Indication is sent in the same direction
as the user traffic impacted by the defect.
Generally, a PE cannot detect transmit defects directly and will
therefore need to be notified of AC transmit or PW transmit defects
by other devices.
In Figure 2, PE1 may be notified of a transmit defect in the AC by
receiving a Reverse Defect indication, e.g., ATM RDI, from CE1. This
defect relates to the traffic sent by PE1 to CE1 on the AC.
Similarly, PE1 may be notified of a transmit defect in the PW by
receiving a Reverse Defect indication from PE2. If PW status is used
for fault notification, this message will indicate a Local PSN
facing PW (ingress) Receive Fault or a Local Attachment Circuit
(egress) Transmit Fault at PE2. This defect impacts the traffic sent
by PE1 to CE2. As a result, PE1 enters the PW transmit defect state.
Note that a Reverse Defect indication is sent in the reverse
direction to the user traffic impacted by the defect.
The procedures outlined in this document define the entry and exit
criteria for each of the four states with respect to the set of PW
services within the document scope and the consequent actions that
PE1 must perform.
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When a PE enters both receive and transmit defect states related to
the same PW service, then the receive defect takes precedence over
transmit defect in terms of the consequent actions.
6. VPWS OAM Modes
A heterogeneous VPWS forwards packets between an AC and a PW of
different types. It thus implements both NS OAM and PW OAM
mechanisms.
PW OAM defect notification messages and NS OAM messages are
described in [OAM-MSG]. Ethernet NS OAM messages are described in
[MPLS-ETH-OAM].
Two different OAM modes are defined in [OAM-MSG], the distinction
being the method of mapping between the NS and PW OAM defect
notification messages.
The first mode, illustrated in Figure 3, is called the "single
emulated OAM loop" mode. Here a single end-to-end NS OAM loop is
emulated by transparently passing NS OAM messages over the PW. Note
that the PW OAM is shown outside the PW in Figure 3, as it is
transported in LDP messages or in the associated channel, not inside
the PW itself.
|<----- AC ----->|<----- PW ----->|<----- AC ----->|
| | | |
___ ===============_
|CE|---=NS-OAM=>---(---=NS-OAM=>---)---=NS-OAM=>---|CE|
=============== /
\ /
---=PW-OAM=>---
Figure 3: Single Emulated OAM Loop mode
The second OAM mode operates three OAM loops joined at the AC/PW
boundaries of the PEs. This is referred to as the "coupled OAM
loops" mode and is illustrated in Figure 4. Note that in contrast to
Figure 3, NS OAM messages are never carried over the PW.
|<----- AC ----->|<----- PW ----->|<----- AC ----->|
| | | |
__ ===============__
|CE|---=NS-OAM=>---(---------------)---=NS-OAM=>---|CE|
\ =============== /
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\ /
\ /
-------=PW-OAM=>------
Figure 4: Coupled OAM Loops mode
The coupled OAM loops mode implements the following behavior:
a. The upstream PE (PE1) MUST terminate and translate a received
NS defect notification message into a PW defect notification
message.
b. The upstream PE MUST signal local failures affecting its local
AC using PW defect notification messages to the downstream PE.
c. The upstream PE MUST signal local failures affecting the PW
using PW defect notification messages.
d. The downstream PE (PE2) MUST insert NS defect notification
messages into the AC when it detects or is notified of defects
in the PW or remote AC. This includes translating received PW
defect notification messages into NS defect notification
messages.
Table 1 summarizes the OAM mode used with each type of VPWS covered
in this document.
-----------------------------------------------------------------
|VPWS Type | Single Emulated | Coupled OAM |
| | OAM Loop Mode | Loops Mode |
------------------------------------------------------------------
|FR-ATM Interworking | | |
|- ATM cell mode PW | X | |
------------------------------------------------------------------
|FR-ATM Interworking | | |
|- FR or AAL5 PDU/SDU PW| | X |
------------------------------------------------------------------
|Ethernet Interworking | | X |
------------------------------------------------------------------
|IP Interworking | | X |
-----------------------------------------------------------------
Table 1: Summary of Heterogeneous VPWS OAM Modes
7. PW Defect State Entry/Exit
The details of the PW transmit and receive defect state entry/exit
criteria are described in Section 8.2 of [OAM-MSG].
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The consequent actions for an ATM AC are described in sections 9.3.1
and 9.3.2 of [OAM-MSG].
The consequent actions for a FR AC are described in sections 10.3.1
and 10.3.2 of [OAM-MSG].
The consequent actions for an Ethernet AC are described in sections
5.1 through 5.4 of [MPLS-ETH-OAM].
8. ATM AC Defect State Entry/Exit
The details of the ATM AC receive and transmit defect state
entry/exit criteria are described in sections 9.1 and 9.2
respectively of [OAM-MSG].
The consequent actions are described in sections 9.3.4 and 9.3.5 of
[OAM-MSG].
Note that all interworking VPWS covered in this document make use of
ATM VC as the AC. ATM VP cannot be used as a SAP in an interworking
VPWS. Therefore only ATM F5 OAM messages are relevant.
9. FR AC Defect State Entry/Exit
The details of the FR AC receive and transmit defect state
entry/exit criteria are described in sections 10.1 and 10.2
respectively of [OAM-MSG].
The consequent actions are described in sections 10.3.4 and 10.3.5
of [OAM-MSG]. Note however that if the FR AC is part of a FR-ATM
interworking VPWS operating in the single emulated OAM loop mode,
then the consequent actions are described sections 9.3.4 and 9.3.5
of [OAM-MSG].
10. Ethernet AC Defect State Entry/Exit
The details of the Ethernet AC receive and transmit defect state
entry/exit criteria are described in sections 4.1 and 4.2
respectively of [MPLS-ETH-OAM].
The consequent actions are described in sections 5.5 through 5.8 of
[MPLS-ETH-OAM].
11. Security Considerations
The mapping messages described in this document do not change the
security functions inherent in the actual messages. All generic
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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 RFC 5085 for VCCV apply to
the OAM messages thus transferred. Security considerations
applicable to the PWE3 control protocol of RFC 4447 Section 8.2
apply to OAM indications transferred using the LDP status message.
12. IANA Considerations
This document requires no IANA actions.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[OAM-MSG] Nadeau, T., et al., ''Pseudo Wire (PW) OAM Message Mapping'',
RFC 6310, April 2011.
[MPLS-ETH-OAM] Qiu, R., Mohan, D., Bitar, N., DeLord, S., Niger, P.,
and A. Sajassi, "MPLS and Ethernet OAM Interworking",
draft-ietf-pwe3-mpls-eth-oam-iwk-04 (work in progress), March
2011.
13.2. Informative References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating
MPLS in IP or Generic Routing Encapsulation (GRE)",
RFC 4023, March 2005.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
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[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", RFC 5885, June 2010.
[ARP-MEDIATION] Shah, H., et al., ''ARP Mediation for IP interworking
of Layer 2 VPN'', draft-ietf-l2vpn-arp-mediation-18.txt, October
2011.
[FRF8.2] Frame Relay Forum, ''FRF 8.2 - Frame Relay / ATM PVC Service
Interworking Implementation Agreement'', February 2004.
[L2VPN-FRMK] Andersson, L. et. al., "L2VPN Framework", RFC 4664,
September 2006.
14. Editor's Addresses
Mustapha Aissaoui
Alcatel-lucent
Email: mustapha.aissaoui@alcatel-lucent.com
Dave Allan
Ericsson
david.i.allan@ericsson.com
Peter B. Busschbach
Alcatel-Lucent
Email: peter.busschbach@alcatel-lucent.com
Thomas Nadeau
CA Technologies
thomas.nadeau@ca.com
Monique Morrow
Cisco Systems, Inc.
EMail: mmorrow@cisco.com
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