MPLS Working Group Dave Allan, Ed.
Internet Draft Ericsson
Intended status: Standards Track
Expires: April 2011 George Swallow Ed.
Cisco Systems, Inc
John Drake Ed.
Juniper
October 22, 2010
Proactive Connectivity Verification, Continuity Check and Remote
Defect indication for MPLS Transport Profile
draft-ietf-mpls-tp-cc-cv-rdi-02
Abstract
Continuity Check (CC), Proactive Connectivity Verification (CV) and
Remote Defect Indication (RDI) functionalities are required for MPLS-
TP OAM.
Continuity Check monitors the integrity of the continuity of the LSP
for any loss of continuity defect. Connectivity verification monitors
the integrity of the routing of the LSP between sink and source for
any connectivity issues. RDI enables an End Point to report, to its
associated End Point, a fault or defect condition that it detects on
a PW, LSP or Section.
This document specifies methods for proactive CV, CC, and RDI for
MPLS-TP Label Switched Path (LSP), PWs and Sections using
Bidirectional Forwarding Detection (BFD).
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [1].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance
with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet
Engineering Task Force (IETF), its areas, and its working
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groups. Note that other groups may also distribute working
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Internet-Drafts are draft documents valid for a maximum of six
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documents at any time. It is inappropriate to use Internet-
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This Internet-Draft will expire on November 28, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction...................................................3
1.1. Authors......................................................4
2. Conventions used in this document..............................4
2.1. Terminology..................................................4
2.2. Issues for discussion........................................5
3. MPLS CC, proactive CV and RDI Mechanism using BFD..............5
3.1. ACH code points for CC and proactive CV......................6
3.2. MPLS BFD CC Message format...................................6
3.3. MPLS BFD proactive CV Message format.........................7
3.4. BFD Session in MPLS-TP terminology...........................7
3.5. BFD Profile for MPLS-TP......................................8
3.5.1. Session initiation.........................................9
3.5.2. Defect entry criteria......................................9
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3.5.3. Defect entry consequent action............................10
3.5.4. Defect exit criteria......................................11
3.5.5. State machines............................................11
3.5.6. Configuration of MPLS-TP BFD sessions.....................14
3.5.7. Discriminator values......................................14
4. Acknowledgments...............................................15
5. IANA Considerations...........................................15
6. Security Considerations.......................................15
7. References....................................................15
7.1. Normative References........................................15
7.2. Informative References......................................16
1. Introduction
In traditional transport networks, circuits are provisioned on two or
more switches. Service Providers (SP) need OAM tools to detect mis-
connectivity and loss of continuity of transport circuits. Both PWs
and MPLS-TP LSPs [7] emulating traditional transport circuits need to
provide the same CC and proactive CV capabilities as required in
draft-ietf-mpls-tp-oam-requirements[3]. This document describes the
use of BFD for CC, proactive CV, and RDI of a PW, LSP or SPME between
two Maintenance Entity Group End Points (MEPs).
As described in [9], Continuity Check (CC) and Proactive Connectivity
Verification (CV) functions are used to detect loss of continuity
(LOC), and unintended connectivity between two MEPs (e.g. mismerging
or misconnectivity or unexpected MEP).
The Remote Defect Indication (RDI) is an indicator that is
transmitted by a MEP to communicate to its peer MEP that a signal
fail condition exists. RDI is only used for bidirectional LSPs and is
associated with proactive CC & CV packet generation.
This document specifies the BFD extension and behavior to satisfy the
CC, proactive CV monitoring and the RDI functional requirements for
both co-routed and associated bi-directional LSPs. Supported
encapsulations include GAL/G-ACh, VCCV and UDP/IP. Procedures for
uni-directional LSPs are for further study.
The mechanisms specified in this document are restricted to BFD
asynchronous mode.
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1.1. Authors
David Allan, John Drake, George Swallow, Annamaria Fulignoli, Sami
Boutros, Siva Sivabalan, David Ward, Martin Vigoureux.
2. Conventions used in this document
2.1. Terminology
ACH: Associated Channel Header
BFD: Bidirectional Forwarding Detection
CV: Connectivity Verification
GAL: Generalized Alert Label
LDI: Link Down Indication
LKI: Lock Instruct
LKR: Lock Report
LSR: Label Switching Router
MEG: Maintenance Entity Group
MEP: Maintenance Entity Group End Point
MIP: Maintenance Entity Group Intermediate Point
MPLS-OAM: MPLS Operations, Administration and Maintenance
MPLS-TP: MPLS Transport Profile
MPLS-TP LSP: Uni-directional or Bidirectional Label Switch Path
representing a circuit
MS-PW: Multi-Segment PseudoWire
NMS: Network Management System
PW: Pseudo Wire
RDI: Remote Defect Indication.
SPME: Sub-Path Maintenance Entity
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TTL: Time To Live
TLV: Type Length Value
VCCV: Virtual Circuit Connectivity Verification
2.2. Issues for discussion
1) Requirement for additional BFD diagnostic codes?
1. When periodicity of CV cannot be supported
3. MPLS CC, proactive CV and RDI Mechanism using BFD
This document proposes distinct encapsulations and code points for
ACh encapsulated BFD depending on whether the mode of operation is CC
or CV:
o CC mode: defines a new code point in the Associated Channel Header
(ACH) described in [2].In this mode Continuity Check and RDI
functionalities are supported.
o CV mode: defines a new code point in the Associated Channel Header
(ACH) described in [2]. The ACH with "MPLS Proactive CV" code
point indicates that the message is an MPLS BFD proactive CV and
CC message and CC, CV and RDI functionalities are supported.
RDI: is communicated via the BFD diagnostic field in BFD CC and CV
messages. It is not a distinct PDU. A sink MEP will encode a
diagnostic code of "1- Control detection time expired" when the
interval times detect multipler have been exceeded, and with "3 -
neighbor signaled session down" as a consequence of the sink MEP
receiving AIS with LDI set. A sink MEP that has started sending diag
code 3 will NOT change it to 1 when the detection timer expires.
In accordance with RFC 5586, when these packets are encapsulated in
an IP header the fields in the IP header are set as defined in RFC
5884. It should also be noted that existing ACh code points and
mechanisms for negotiating the control channel and connectivity
verification (i.e. OAM functions) between PEs are specified for
VCCV[6].
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3.1. ACH code points for CC and proactive CV
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags |0xHH BFD CC/CV Code Point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ACH Indication of MPLS-TP Connectivity Verification
The first nibble (0001b) indicates the ACH.
The version and the flags are set to 0 as specified in [2].
The code point is either
- BFD CC code point = 0xHH. [HH to be assigned by IANA from the PW
Associated Channel Type registry.] or,
- BFD proactive CV code point = 0xHH. [HH to be assigned by IANA from
the PW Associated Channel Type registry.]
Both CC and CV modes apply to PWs, MPLS LSPs (including tandem
connection monitoring), and Sections.
CC and CV operation can be simultaneously employed on an ME within a
single BFD session. The expected usage is that normal operation is to
send CC BFD PDUs with every nth BFD PDU augmented with a source MEP
ID and identified as requiring additional processing by the different
ACh channel type.
3.2. MPLS BFD CC Message format
The format of an MPLS CC Message is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | 0xHH BFD CC Code point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS CC Message
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3.3. MPLS BFD proactive CV Message format
The format of an MPLS CV Message is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | 0xHH BFD CV Code Point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Unique MEP-ID of source of the BFD packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: MPLS CV Message
As shown in Figure 3, BFD Control packet as defined in [4] is
transmitted as MPLS labeled packets along with the ACH. Appended to
the BFD control packet is a MEP Source ID TLV. The length in the BFD
control packet is as per [4]. There are 4 possible Source MEP TLVs
(corresponding to the MEP IDs defined in [8] [type fields to be
assigned by IANA]. The type fields are:
X1 - ICC encoded MEP ID
X2 - LSP-MEP_ID
X3 - PW MEP ID
X4 - PW Segment endpoint ID
When GAL label is used, the TTL field of the GAL MUST be set to at
least 1, and the GAL will be the end of stack label (S=1).
3.4. BFD Session in MPLS-TP terminology
A BFD session corresponds to a CC or a proactive CV OAM instance in
MPLS-TP terminology.
A BFD session is enabled when the CC or proactive CV functionality is
enabled on a configured Maintenance Entity (ME)..
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On a Sink MEP, a BFD session can be in DOWN, INIT or UP state as
detailed in [4].
When on a ME the CC or proactive CV functionality is disabled, the
BFD session transitions to the ADMIN DOWN State and the BFD session
ends.
A new BFD session is initiated when the operator enables or re-
enables the CC or CV functionality on the same ME.
3.5. BFD Profile for MPLS-TP
BFD MUST operate in asynchronous mode. In this mode, the BFD Control
packets are periodically sent at configurable time rate. This rate is
typically a fixed value for the lifetime of the session. In the rare
circumstance where an operator has a reason to change session
parameters, the session must be moved to the ADMIN DOWN state.
Poll/final discipline can only used for VCCV and UDP/IP encapsulated
BFD.
The transport profile is designed to operate independent of the
control plane; hence the C bit SHOULD be set.
This document specifies bi-directional BFD for p2p transport LSPs,
hence the M bit MUST be clear.
There are two modes of operation for bi-directional LSPs. One in
which the session state of both directions of the LSP is coordinated
and one constructed from BFD sessions in such a way that the two
directions operate independently. A single bi-directional BFD session
is used for coordinated operation. Two independent BFD sessions are
used for independent operation.
Coordinated operation is as described in [4]. Independent operation
requires clarification of two aspects of [4]. Independent operation
is characterized by the setting of MinRxInterval to zero by the MEP
that is typically the session originator (referred to as the source
MEP), and there will be a session originator at either end of the bi-
directional LSP. Each source MEP will have a corresponding sink MEP
that has been configured to a Tx interval of zero.
The base spec is unclear on aspects of how a MEP with a BFD transmit
rate set to zero behaves. One interpretation is that no periodic
messages on the reverse component of the bi-directional LSP originate
with that MEP, it will only originate messages on a state change.
The first clarification is that when a state change occurs a MEP set
to a transmit rate of zero sends BFD control messages with a one
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second period on the reverse component until such time that the state
change is confirmed by the session peer. At this point the MEP set to
a transmit rate of zero can resume quiescent behavior. This adds
robustness to all state transitions in the RxInterval=0 case.
The second is that the originating MEP (the one with a non-zero
TxInterval) will ignore a DOWN state received from a zero interval
peer. This means that the zero interval peer will continue to send
DOWN state messages that include the RDI diagnostic code as the state
change is never confirmed. This adds robustness to the exchange of
RDI indication on a uni-directional failure (for both session types
DOWN with a diagnostic of either control detection period expired or
neighbor signaled session down offering RDI functionality).
A further extension to the base specification is that there are
additional OAM protocol exchanges that act as inputs to the BFD state
machine; these are the Link Down Indication [5] and the Lock
Instruct/Lock Report transactions; Lock Report interaction being
optional.
3.5.1. Session initiation
In all scenarios a BFD session starts with both ends in the DOWN
state. DOWN state messages exchanged include the desired Tx and Rx
rates for the session. If a node cannot support the Min Tx rate
desired by a peer MEP it does not transition from down to the INIT
state and sends a diagnostic code (TBD) indicating that the requested
Tx rate cannot be supported.
Otherwise once a transition from DOWN to INIT has occurred, the
session progresses as per [4]. In both the DOWN and INIT states
messages are transmitted at a rate of one per second and the defect
detection interval is fixed at 3.5 seconds. On transition to the UP
state message periodicity changes to the negotiated rate and the
detect interval switches to detect multiplier times the session
peer's Tx Rate.
3.5.2. Defect entry criteria
There are further defect criteria beyond those that are defined in
[4] to consider given the possibility of mis-connectivity and mis-
configuration defects. The result is the criteria for a LSP direction
to transition from the defect free state to a defect state is a
superset of that in the BFD base specification [4].
The following conditions cause a MEP to enter the defect state for CC
or CV:
1. BFD session times out (Loss of Continuity defect).
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2. Receipt of a link down indication.
3. Receipt of an unexpected M bit (Session Mis-configuration
defect).
And the following will cause the MEP to enter the defect state for CV
operation
1. BFD control packets are received with an unexpected
encapsulation (mis-connectivity defect), these include:
- a PW receiving a packet with a GAL
- an LSP receiving an IP header instead of a GAL
(note there are other possibilities that can also alias as an
OAM packet)
2. Receipt of an unexpected globally unique Source MEP identifier
(Mis-connectivity defect).
3. Receipt of an unexpected session discriminator in the your
discriminator field (mis-connectivity defect).
4. Receipt of an expected session discriminator with an unexpected
label (mis-connectivity defect).
The effective defect hierarchy (order of checking) is
1. Receiving nothing.
2. Receiving link down indication.
3. Receiving from an incorrect source (determined by whatever
means).
4. Receiving from a correct source (as near as can be determined),
but with incorrect session information).
5. Receiving control packets in all discernable ways correct.
3.5.3. Defect entry consequent action
Upon defect entry a sink MEP will assert signal fail into any client
(sub-)layers. It will also communicate session DOWN to its session
peer.
The blocking of traffic as consequent action MUST be driven only by a
defect's consequent action as specified in draft-ietf-mpls-tp-oam-
framework [9] section 5.1.1.2.
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When the defect is mis-branching, the LSP termination will silently
discard all non-oam traffic received.
3.5.4. Defect exit criteria
3.5.4.1. Exit from a Loss of continuity defect
For a coordinated session, exit from a loss of connectivity defect is
as described in figure 4 which updates [4].
For an independent session, exit from a loss of connectivity defect
occurs upon receipt of a well formed control packet from the peer MEP
as described in figures 5 and 6.
3.5.4.2. Exit from a session mis-configuration defect
[editors: for a future version of the document]
3.5.4.3. Exit from a mis-connectivity defect
[Editors node: The shift to CC with interleaved CV suggests the CV
periodicity may not be known by a sink MEP, hence exit criteria from
a mis-connectivity defect may not be able to be established. We
suggest two possible resolutions for this:
1. Exit criteria is manual intervention.
2. A minimum CV insertion rate (say 1/sec) be specified such that
the exit criteria be specified as no mis-connected CV PDUs be
received for a minimum of 3 times the minimum insertion rate]
3.5.5. State machines
The following state machines update [4]. They have been modified to
include AIS with LDI set and LKI as inputs to the state machine and
to clarify the behavior for independent mode. LKR is an optional
input.
The coordinated session state machine has been augmented to indicate
AIS with LDI set and optionally LKR as inputs to the state machine.
For a session that is in the UP state, receipt of AIS with LDI set or
optionally LKR will transition the session into the DOWN state.
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+--+
| | UP, ADMIN DOWN, TIMER, AIS-LDI, LKR
| V
DOWN +------+ INIT
+------------| |------------+
| | DOWN | |
| +-------->| |<--------+ |
| | +------+ | |
| | | |
| | ADMIN DOWN,| |
| |ADMIN DOWN, DOWN,| |
| |TIMER TIMER,| |
V |AIS-LDI,LKR AIS-LDI,LKR | V
+------+ +------+
+----| | | |----+
DOWN| | INIT |--------------------->| UP | |INIT, UP
+--->| | INIT, UP | |<---+
+------+ +------+
Figure 4: State machine for coordinated session operation
For independent mode, there are two state machines. One for the
source MEP (who requested MinRxInterval=0) and the sink MEP (who
agreed to MinRxInterval=0).
The source MEP will not transition out of the UP state once
initialized except in the case of a forced ADMIN DOWN. Hence AIS-with
LDI set and optionally LKR do not enter into the state machine
transition from the UP state, but do enter into the INIT and DOWN
states.
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+--+
| | UP, ADMIN DOWN, TIMER
| V
DOWN +------+ INIT
+------------| |------------+
| | DOWN | |
| +-------->| |<--------+ |
| | +------+ | |
| | | |
| |ADMIN DOWN ADMIN DOWN | |
| |TIMER, | |
| |AIS-LDI, | |
V |LKR | V
+------+ +------+
+----| | | |----+
DOWN| | INIT |--------------------->| UP | | INIT, UP, DOWN,
+--->| | INIT, UP | |<---+ AIS-LDI, LKR
+------+ +------+
Figure 5: State machine for source MEP for independent session
operation
The sink MEP state machine (for which the transmit interval has been
set to zero) is modified to:
1) Permit direct transition from DOWN to UP once the session has been
initialized. With the exception of via the ADMIN DOWN state, the
source MEP will never transition from the UP state, hence in normal
unidirectional fault scenarios will never transition to the INIT
state.
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+--+
| | ADMIN DOWN, TIMER, AIS-LDI, LKR
| V
DOWN +------+ INIT, UP
+------------| |------------+
| | DOWN | |
| +-------->| |<--------+ |
| | +------+ | |
| | | |
| | ADMIN DOWN,| |
| |ADMIN DOWN, TIMER, | |
| |TIMER, DOWN, | |
| |AIS-LDI, AIS-LDI, | V
V |LKR LKR | |
+------+ +------+
+----| | | |----+
DOWN| | INIT |--------------------->| UP | |INIT, UP
+--->| | INIT, UP | |<---+
+------+ +------+
Figure 6: State machine for the sink MEP for independent session
operation
3.5.6. Configuration of MPLS-TP BFD sessions
[Editors note, for a future revision of the document]
3.5.7. Discriminator values
In the BFD control packet the discriminator values have either local
to the sink MEP or no significance (when not known).
My Discriminator field MUST be set to a nonzero value (it can be a
fixed value), the transmitted your discriminator value MUST reflect
back the received value of My discriminator field or be set to 0 if
that value is not known.
Although the BFD base specification permits an implementation to
change the my discriminator field at arbitrary times, this is not
permitted for CV mode in order to avoid race conditions in mis-
connectivity defects.
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4. Acknowledgments
To be added in a later version of this document
5. IANA Considerations
To be added in a later version of this document
6. Security Considerations
The security considerations for the authentication TLV need further
study.
Base BFD foresees an optional authentication section (see [4]
section 6.7); that can be extended also to the tool proposed in
this document.
Authentication methods that require checksum calculation on the
outgoing packet must extend the checksum also on the ME
Identifier Section. This is possible but seems uncorrelated with
the solution proposed in this document: it could be better to
use the simple password authentication method.
7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Bocci, M. et al., " MPLS Generic Associated Channel ", RFC
5586 , June 2009
[3] Vigoureux, M., Betts, M. and D. Ward, "Requirements for
Operations Administration and Maintenance in MPLS
Transport Networks", RFC5860, May 2010
[4] Katz, D. and D. Ward, "Bidirectional Forwarding
Detection", RFC 5880, June 2010
[5] Swallow, G. et al., "MPLS Fault Management OAM", draft-
ietf-mpls-tp-fault-02 (work in progress), July 2010
[6] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
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7.2. Informative References
[7] Bocci, M., et al., "A Framework for MPLS in Transport
Networks", RFC5921, July 2010
[8] Bocci, M. and G. Swallow, "MPLS-TP Identifiers", draft-
swallow-mpls-tp-identifiers-02 (work in progress), July
2010
[9] Allan, D., and Busi, I. "MPLS-TP OAM Framework", draft-
ietf-mpls-tp-oam-framework-09 (work in progress), October
2010
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Authors' Addresses
Dave Allan
Ericsson
Email: david.i.allan@ericsson.com
John Drake
Juniper
Email: jdrake@juniper.net
George Swallow
Cisco Systems, Inc.
Email: swallow@cisco.com
Annamaria Fulignoli
Ericsson
Email: annamaria.fulignoli@ericsson.com
Sami Boutros
Cisco Systems, Inc.
Email: sboutros@cisco.com
Martin Vigoureux
Alcatel-Lucent
Email: martin.vigoureux@alcatel-lucent.com
Siva Sivabalan
Cisco Systems, Inc.
Email: msiva@cisco.com
David Ward
Juniper
Email: dward@juniper.net
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