Network Working Group T. Nadeau (Ed)
Internet Draft C. Pignataro (Ed)
Expiration Date: April 2007 Cisco Systems, Inc.
R. Aggarwal (Ed)
Juniper Networks
October 2006
Pseudo Wire Virtual Circuit Connectivity Verification (VCCV)
draft-ietf-pwe3-vccv-11.txt
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Abstract
This document describes Virtual Circuit Connection Verification
(VCCV) which provides a control channel that is associated
with a pseudo wire (PW), as well as the corresponding
operations and management functions such as connectivity
verification to be used over that control channel. VCCV
applies to all supported access circuit and transport types
currently defined for PWs.
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Table of Contents
1 Specification of requirements .......................... 4
2 Introduction ........................................... 4
3 Overview of VCCV ....................................... 5
4 CC Types and CV Types ................................... 5
4.1 Bidirectional Forwarding Detection ...................... 7
4.1.1 BFD Encapsulation ....................................... 7
5 VCCV Control Channel for MPLS PSN ....................... 7
5.1 Inband VCCV (Type 1) .................................... 7
5.2 Out-of-Band VCCV (Type 2) ............................... 8
5.3 TTL Expiry VCCV (Type 3) ................................ 8
5.4 VCCV Connectivity Verification Types .................... 8
5.4.1 MPLS LSP Ping ........................................... 9
5.5 VCCV Capability Advertisement for MPLS PSN .............. 10
5.5.1 VCCV Capability Advertisement LDP Sub-TLV ............... 11
6 VCCV Control Channel for L2TPv3/IP PSN ................. 12
6.1 L2TPv3 VCCV Message .................................... 13
6.1.1 L2TPv3 VCCV using ICMP Ping ............................ 13
6.1.2 L2TPv3 VCCV using BFD .................................. 13
6.2 L2TPv3 VCCV Capability Indication ...................... 13
6.2.1 L2TPv3 VCCV Capability AVP ............................. 13
6.3 L2TPv3 VCCV Operation .................................. 14
7. Capability Advertisement Preference Order ............... 14
8. IANA Considerations .................................... 14
8.1 VCCV Parameter ID ...................................... 14
8.1.1 Control Channel Types (CC Types) ........................ 15
8.1.2 Connectivity Verification Types (CV Types) .............. 15
8.1.3 Channel Type ............................ .............. 15
8.2 L2TPv3 Assignments ..................................... 15
8.2.1 Control Message Attribute Value Pairs (AVPs) ........... 15
8.2.2 Default L2-Specific Sublayer bits ...................... 15
8.2.3 ATM-Specific Sublayer bits ............................. 15
8.2.4 VCCV Capability AVP Values ............................. 15
9 Security Considerations ................................ 15
10 Acknowledgements ....................................... 17
11 References ............................................. 17
11.1 Normative References ................................... 17
11.2 Informative References ................................. 18
12 Editor Information ...................................... 18
13 Contributor Information ................................ 19
14 Intellectual Property Statement ........................ 20
15 Full Copyright Statement ............................... 20
1. Specification of requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
As network operators deploy pseudo wire (PW) services, fault detec-
tion and diagnostic mechanisms particularly for the PSN portion of
the network are pivotal. Specifically, the ability to provide end-to-
end fault detection and diagnostics for an emulated PW service is
critical for the network operator. Operators have indicated in
[RFC4377][RFC3916] that such a tool is required for PW deployments.
This document describes procedures for a PSN-agnostic fault
detection and diagnostics tool called Virtual Circuit Connection
Verification (VCCV).
|<----- Pseudo Wire ---->|
| |
Attachment or | |<-- PSN Tunnel -->| | Attachment or
Virtual | | | | Virtual
Circuit V V V V Circuit
| +----+ +----+ |
+----+ | | PE1|==================| PE2| | +----+
| |----------|............PW1.............|----------| |
| CE1| | | | | | | |CE2 |
| |----------|............PW2.............|----------| |
+----+ | | |==================| | | +----+
^ +----+ +----+ | ^
| Provider Edge 1 Provider Edge 2 |
| |
|<--------------- Emulated Service --------------->|
Customer Customer
Edge 1 Edge 2
Figure 2 illustrates the network reference model for point-to-point
PWs.
|<-------------- Emulated Service ---------------->|
| |
| <---------- VCCV ----------> |
| |<------- Pseudo Wire ------>| |
| | | |
| | |<-- PSN Tunnel -->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | | PE1|==================| PE2| | +-----+
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| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | ^ +-----+
^ | +----+ +----+ | | ^
| | Provider Edge 1 Provider Edge 2 | |
| | | |
Customer | | Customer
Edge 1 | | Edge 2
| |
| |
Native service Native service
Figure 1: PWE3 VCCV Operation Reference Model
Figure 1 depicts the basic functionality of VCCV. VCCV provides
several means of creating a control channel between PEs that
attach the PW under test.
+-------------+ +-------------+
| Layer2 | | Layer2 |
| Emulated | < Emulated Service > | Emulated |
| Services | | Services |
+-------------+ +-------------+
| | VCCV/PW | |
|Demultiplexer| < Control Channel > |Demultiplexer|
+-------------+ +-------------+
| PSN | < PSN Tunnel > | PSN |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
| |
| ____ ___ ____ |
| _/ ___/ \ _/ __ |
| / \__/ _ |
| / \ |
---------| MPLS or IP Network |-----
| /
| ___ ___ __ ___/
\_/ ____/ ___/ ____/
Figure 2: PWE3 Protocol Stack Reference Model
including the VCCV control channel.
Figure 2 depicts how the VCCV control channel is associated with the
pseudo wire. Ping and other IP messages are encapsulated using the
PWE3 encapsulation as described below in sections 5 and 6. These mes-
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sages, referred to as VCCV messages, are exchanged only after the
desire to exchange such traffic has been negotiated between the PEs
(see section 8).
3. Overview of VCCV
VCCV defines a set of messages that are exchanged between PEs to ver-
ify connectivity of the pseudo wire. To make sure that VCCV packets
follow the same path as the PW data flow, they SHOULD be encapsulated
with the same PW demultiplexer and trasported over the same PSN
tunnel. For example, if MPLS is the PSN in use, then the same
label shim header (and label stack) MUST be incorporated. The only
cases where this might not be possible is when out-of-band VCCV modes
are used which require this encapsulation to be altered; however,
these modes are discouraged.
VCCV can be used both as a fault detection and/or a diagnostic
tool for pseudowires. An operator can periodically invoke VCCV
for proactve connectivity verification on an active pseudowire,
or on an ad hoc or as-needed as a means of manual
connectivity verification. When invoking VCCV, the operator
triggers a combination of one of its various Connectivity Check
types (CC Type) and one of its various Connectivity Verification
(CV) Types. These include LSP-Ping, L2TPV3, or ICMP Ping [RFC792]
modes and are applicable depending on the underlying PSN.
Since a pseudowire service is bi-directional, the reply MAY be sent
in-band over the PW in the reverse direction. Responses MUST
be encapsulated so that they follow the return path of
the pseudowire in this case. In-band responses MUST be attempted
first. If an in-band test fails, the operator is advised to
then use a subsequent test using an out-of-band reply mode such
as Reply Mode 4 from [RFC4379], which will return the result
to the sender via an application level control channel to
determine the fault's direction.
The control channel maintained with VCCV can carry fault detection
status across a pseudowire and convey this information between
the endpoints of the pseudowire. Furthermore, this information
can then be translated into the native OAM status codes used by
the native access technologies, such as ATM or Ethernet. The
specific details of such status interworking is out of the scope
of this document, and is only noted here to illustrate the
utility of VCCV for such purposes. More complete details can
be found in [OAM-MAP].
4. CC Types and CV Types
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VCCV can support several types of connectivity verification
types (CV types) or protocols within its control channel,
but only one MUST be used once a PE has begun transmitting one.
The specific one chosen is based on the preferred order
specified below in section 7. If another is desired to be
used once a PE has begun to use one, the pseudowire MUST
be re-signaled. The specific type or types of VCCV packets
accepted by a router are indicated during capability
advertisement as described in section 4.5. The various VCCV
CV types supported MUST be used only when they apply
to the context of the PW demultiplexor in use. For example,
LSP Ping type should only be used when MPLS is utilized as
the PSN.
These type indicator fields are defined as a bitmask used
to indicate the specific CV or CC type or types (i.e.: none,
one or more) of control channel packets that may be sent on
the VCCV control channel. These values represent the numerical
value corresponding to the actual bit being set in the
bitfield. The definintion of each CV and CC Type is dependent
on the context within which it is defined; please refer to
the specific MPLS or L2TPv3 sections below.
The defined values for CC Types are for MPLS PWs are:
0x01 Type 1: PWE3 control word with 0001b as first nibble
as defined in [RFC4385].
0x02 Type 2: MPLS Router Alert Label.
0x04 Type 3: MPLS PW Demultiplexor Label TTL = 1 (Type 3).
The defined values for CC Types are for L2TPv3 PWs are:
0x01 L2-Specific Sublayer with V-bit set.
0x02 Reserved for future use.
0x04 Reserved for future use.
The defined values for CV Types are for MPLS PWs are:
0x01 ICMP Ping.
0x02 LSP Ping.
0x04 BFD for PW Fault Detection Only.
0x08 BFD for PW Fault Detection and AC/PW Fault
Status Signaling.
0x10 BFD for PW Fault Detection Only. Carrying BFD payload
without IP headers.
0x20 BFD for PW Fault Detection and AC/PW Fault
Status Signaling. Carrying BFD payload without IP headers.
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The defined values for CV Types are for L2TPv3 PWs are:
0x01 ICMP Ping.
0x02 Reserved for future use.
0x04 BFD for PW Fault Detection Only.
0x08 BFD for PW Fault Detection and AC/PW Fault
Status Signaling.
0x10 BFD for PW Fault Detection Only. Carrying BFD payload
without IP headers.
0x20 BFD for PW Fault Detection and AC/PW Fault
Status Signaling. Carrying BFD payload without IP headers.
It should be noted that two different pairs of CV Types have been
defined when BFD is used. If a capability advertisement is received
with both 0x04 and 0x08 types indicated, the PE MUST ignore the 0x08
bit as if it were set to 0. If a capability advertisement is
received with both 0x10 and 0x20 types indicated, the PE MUST ignore
the 0x20 bit as if it were set to 0. In the case of type 0x08 or
0x20, the AC and PW status SHOULD be conveyed via BFD status codes
as specified in [OAM-MAP]. However, this type SHOULD NOT be used
when a control protocol such as LDP or L2TPV3 is available that can
signal the AC/PW status to the remote endpoint of the PW
In the case of type 0x04 or 0x10, BFD is used exclusively to detect
faults on the PW and the status of those faults should be conveyed
using some means other than BFD, such as using LDP status messages
when using MPLS as a transport, or the Circuit Status
AVP in an L2TPv3 SLI message for L2TPv3 (see [RFC3931]).
If none of the types above are supported, the entire CV Type
Indicator field SHOULD be transmitted as 0x00 to indicate this
to the peer.
If no capability is signaled, then the peer MUST assume that
the peer has no VCCV capability and follow the procedures
specified in this document for this case.
4.1 Bidirectional Forwarding Detection
When heart-beat indication is necessary for one or more PWs, the
Bidirectional Forwarding Detection (BFD) [BFD] provides a
means of continuous monitoring of the PW data path and
propagation of forward and reverse defect indications.
In order to use BFD, both ends of the PW connection must have
signaled the existence of a control channel and the ability to run
BFD on it. Once a node has both signaled and received signaling from
its peer of these capabilities, it MUST begin sending BFD control
packets. The packets MUST be sent on the control channel. The use
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of the control channel provides the context required to bind and
bootstrap the BFD session, thus single-hop BFD initialization
procedures are followed [BFD], and BFD MUST be run in asynchronous
mode [BFD].
When one of the PEs (PE2 from Figure 1) doesn't receive control
messages from PE1 (from Figure 1) during the specified amount of
time it declares that the PW in the direction from PE2 to PE1
is down.
It stores the cause (e.g., Diagnostic code 1 - control detection time
expired) and sends a message to PE1 containing this diagnostic code.
This causes PE1 to declare the PW in the direction from PE1 to PE2
is down and it stores as cause: neighbor signaled session down.
Depending on the emulated services, PE2 may send a
forward direction indication (FDI) on its attachment
circuits and PE1 may send an RDI indication on its attachment
circuits [OAM-MAP].
BFD defines the following diagnostics:
0 - No Diagnostic
1 - Control Detection Time Expired
2 - Echo Function Failed
3 - Neighbor Signaled Session Down
4 - Forwarding Plane Reset (Local equipment failure)
5 - Path Down (Alarm Suppression)
6 - Concatenated Path Down (Propagating access link alarm)
7 - Administratively Down
8 - Reverse Concatenated Path Down
Note that the value, 0 is used when the PW is up and 2 is not appli-
cable to asynchronous mode.
In cases where PW or AC status is received from both the signaling
protocol and VCCV via BFD status codes, the following algorithm
should be employed when transitioning the PW state based on these
values:
Transition from any state to "UP" state where the control plane
and BFD status both indicate that the PW is functioning correctly:
if (control plane == "UP" && BFD Status == "UP")
PW status = UP;
Transition from any state to "Down" state where either
the contorl or BFD status indicate that the PW is malfunctioning:
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if (control plane == "UP" || BFD Status == "UP")
PW status = DOWN;
The VCCV message comprises a BFD packet [BFD] encapsulated
as specified by the CV Type (see Section 4.1.1).
4.1.1 BFD Encapsulation
VCCV defines two pairs of CV Types (see above) which specify
two ways in which the VCCV control channel may be encapsualted
when carrying a BFD payload. When the CV Type is either 0x04 or
0x08, the VCCV encapsulation includes the IP/UDP encapsulation
as defined in Section 4 of [BFDV4V61HOP]. However, when CV Type
0x10 or 0x20 is employed, the IP/UDP header is omitted.
In these cases the the corresponding PW CW's or L2SS'
Channel Type field MUST use the value defined in section
8.1.3 as a means of allowing the data plane to demultiplex
the control channel and identify the encased BFD payload.
5. VCCV Control Channel for MPLS PSN
When MPLS is used to transport PW packets, VCCV packets are
carried over the MPLS LSP as defined in this section.
In order to apply IP monitoring tools a PWE3 PW, an operator
may configure VCCV as a control channel for the PW between
the PEs endpoints [RFC3985]. Packets sent across this channel
from the source PE towards the destination PE either as in-band
traffic with the PW's data, or out-of-band. In all cases, the
control channel traffic MUST NOT be forwarded past the PE
endpoints towards the Customer Edge (CE) devices; instead,
they must be intercepted at the PE endpoints for exception
processing.
The capability of which control channel type (CC Type) to
use is advertised by a PE to indicate which of the various
control channel types are supported. Once the receiving PE
has chosen a mode to use, it MUST continue using this mode
until such time as the PW is re-signaled. Thus, if a new CC
type is desired, the PW must be torn-down and re-established.
Ideally such a control channel would be completely inband. When
a control word is present on the PW, it is possible to indi-
cate the control channel by setting a bit in the control word
header.
The following subsections define each of
the currently defined VCCV Control Channel Types (CC Types).
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5.1. Inband VCCV (Type 1)
The PW set-up protocol [RFC4447] determines whether a PW uses a
control word. When a control word is used, it SHOULD have the
following form for the purpose of indicating VCCV control
channel messages. Note that for data, one uses the control
word defined just above the MPLS payload [RFC4385].
The PW Associated Channel for VCCV control channel traffic is
defined as follows in [RFC4385]:
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| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PW Associated Channel Header
The first nibble is set to 0001b to indicate a channel associated
with a pseudowire [RFC4385][RFC4446]. The Version and the Reserved
fields are set to 0, the Version is 0, and the Channel Type is set
to 0x21 for IPv4 and 0x56 for IPv6 payloads. If the payload contains
BFD without IP/UDP headers, it MUST use 0x07 as the Channel Type
(see 8.1.3).
For example, the following is an example of how the ethernet
ACH would be received [RFC4448] containing an LSP Ping payload
corresponding to a choice of CC Type of 0x01 and a CV Type of
0x02:
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| 0 0 0 0 0 0 0 0 0 0 0 | 0x21 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: PW Associated Channel Header for VCCV
It should be noted that although some PW types are not required
to carry the control word, this type of VCCV MUST only be used
for those PW types that do employ the control word when it is
in use.
This is the preferred mode of VCCV operation when the control word
is present.
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5.2. Out-of-Band VCCV (Type 2)
A VCCV control channel can alternatively be created by using the
MPLS router alert label [RFC3032] immediately above the PW label.
It should be noted that this approach MAY result in a differnt
equal cost multi-path (ECMP) hashing behavior than pseudowire
PDUs and thus result in the VCCV control channel traffic taking
a path which differs from that of the actual data traffic under
test.
This is the preferred mode of VCCV operation when the control word
is not present.
5.3. TTL Expiry VCCV (Type 3)
The TTL of the PW label can be set to 1 to force the packet to be
processed within the destination router's control plane. This is
an inband control channel identification mechanism that is an
alternate to section 5.1.
To use this type, the control word MUST be used.
5.4 VCCV Connectivity Verification Types
5.4.1 MPLS LSP Ping
The LSP Ping header MUST be used in accordance with [RFC4379]
and MUST also contain the target FEC Stack containing the
sub-TLV of 8 for the L2 VPN endpoint or 9 or 10 for "FEC 128
Pseudowire" or 11 for the FEC 129 Pseudowire". The sub-TLV
indicates the PW to be verified.
5.5 VCCV Capability Advertisement for MPLS PSN
To permit the indication of the type or types of PW control chan-
nel(s), and connectivity verification mode or modes over a particular
PW, a VCCV parameter is defined below that is used as part of the PW
establishment signaling. When a PE signals a PW and desires PW OAM
for that PW, it MUST indicate this during PW establishment using the
messages defined below. Specifically, for PE MUST include the
VCCV parameter in the PW setup message [RFC4447].
The decision of the type of VCCV control channel is left completely
to the receiving control entity, although the set of choices is
given by the sender in that it indicates the type or types of
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control channels that it can understand. The receiver SHOULD
chose a single control channel type from the choices indicated
based on the order of preference rules specified below in
the section 7 and it MUST continue to use this type for
the duration of the life of the control channel. Changing control
channel types after one has been established to be in use
could potentially cause problems at the receiving end, and
could also lead to interoperability issues, thus it is strongly
discouraged.
When a PE sends a label mapping message for a PW, it uses
the VCCV parameter to indicate the type of OAM control channels
and connectivity verification type or types it is willing to
receive on that PW. The capablity of supporting a control
channel or channels, and connectivity type or types used
over that control channel or channels MUST be signaled before
the remote PE may send VCCV messages, and then only on the
control channel or channels, and using the connectivity
verification type or types indicated.
If a PE receives VCCV messages prior to advertising capability for
this message, it MUST discard these messages and not reply to them.
In this case, the PE SHOULD increment an error counter and optionally
issue a system and/or SNMP notification to indicate to the system
administrator that this condition exists.
When LDP is used as the PW signaling protocol the requesting PE
indicates its configured VCCV capability or capabilities to the
remote PE by including the VCCV parameter with appropriate options
indicating which control channel types it supports in the
interface parameter field of the PW ID FEC TLV (FEC 128) or in
the sub-TLV interface parameter of the Genralized PW ID FEC TLV
(FEC 129). The requesting PE MAY indicate that it supports
multiple control channel options, and in doing so agrees to support
any and all indicated types if transmitted to it, but MUST do so
in accordance with the rules stipulated in section 4.5.1 (VCCV
Capability Advertisement Sub-TLV).
Local policy may direct the PE to support certain OAM capability and
to indicate it. The absence of the VCCV parameter indicates that no
OAM functions are supported by the requesting PE, and thus the
receiving PE MUST NOT send any VCCV control channel traffic to it.
The reception of a VCCV parameter with no options set MUST be
ignored as if one is not transmitted at all.
The receiving PE similarly indicates its supported control channel
types in the response. These may or may not be the same as the
ones that were sent to it. The sender should examine the set that
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is returned to understand which control channels it may establish
with the remote peer. Similarly, it MUST NOT send control channel
traffic to the remove PE for which the remote PE has not indicated
it supports.
The exception to the rules given in the last two paragraphs above
is when one side of the PW indicates no support for VCCV while the
other indicates support for at least one control channel type. In
this case, it is possible for one side of the PW to send VCCV
messages (either requests or replies to requests).
5.5.1 VCCV Capability Advertisement LDP Sub-TLV
[RFC4447] defines an Interface Parameter field in the LDP PW ID
FEC (FEC 128) and an Interface Parameters TLV in the LDP Generalized
PW ID FEC (FEC 129) to signal different capabilities for specific
PWs. An optional sub-TLV parameter is defined to indicate the
capability of supporting none, one or more control channel types
for VCCV. This is the VCCV parameter field. If FEC 128 is used the
VCCV parameter field is carried in the Interface Parameters field.
If FEC 129 is used it is carried as an Interface Parameter sub-TLV
in the Interface Parameters TLV.
The VCCV parameter ID is defined as follows in [RFC4446]:
Parameter ID Length Description
0x0c 4 VCCV
The format of the VCCV parameter field is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0c | 0x04 | CC Types | CV Types |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Control Channel (CC Types) type field defines a bitmask used to
indicate the type of control channel(s) (i.e.: none, one or more)
that a router is capable of receiving control channel traffic on.
If more than one control channel is specified, the router agrees
to accept control traffic over either control channel; however,
see the rules specified in section 6 for more details.
If none of the types are supported, a CC Type Indicator of 0x00
SHOULD be transmitted to indicate this to the peer. However,
if no capability is signaled, then the PE MUST assume that its
peer is incapable of receiving any of the VCCV CC Types and
MUST NOT send any OAM control channel traffic to it. Note that
the CC and CV types definitions are consistent regardless of
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the PW's transport or access circuit type. The CC and CV values
are defined below in Section 4.
6. VCCV Control Channel for L2TPv3/IP PSN
When L2TPv3 is used to setup a PW over an IP PSN, VCCV packets are
carried over the L2TPv3 session as defined in this section. L2TPv3
provides a "Hello" keepalive mechanism for the L2TPv3 control plane
that operates in-band over IP or UDP (see Section 4.4 of [RFC3931]).
This built-in Hello facility provides dead peer and path detection
only for the group of sessions associated with the L2TP Control
Connection. VCCV, however, allows individual L2TP sessions to be
tested. This provides a more granular mechanism which can be used to
troubleshoot potential problems within the dataplane of L2TP
endpoints themselves, or to provide additional connection status of
individual Pseudowires.
The capability of which control channel type (CC Type) to
use is advertised by a PE to indicate which of the various
control channel types are supported. Once the receiving PE
has chosen a mode to use, it MUST continue using this mode
until such time as the PW is re-signaled. Thus, if a new CC
type is desired, the PW must be torn-down and re-established.
In order to carry VCCV messages within an L2TPv3 session data packet,
the PW MUST be established such that an L2-Specific Sublayer (L2SS)
that defines the V-bit is present. This document defines the V-bit
for the Default L2-Specific Sublayer [RFC3931] and the ATM-Specific
Sublayer [RFC4454] using the Bit 0 position (see Section 8.2.2 and
Section 8.2.3). The L2-Specific Sublayer presence and type (either
the Default or a PW-Specific L2SS) is signaled via the L2-Specific
Sublayer AVP, Attribute Type 69, as defined in [RFC3931]. The V-bit
within the L2-Specific Sublayer is used to identify that a VCCV
message follows, and when the V-bit is set the L2SS has the following
format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0 0 0|Version| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L2-Specific Sublayer Format when the V-bit (bit 0) is set
The VCCV messages are distinguished from user data by the V-bit. The
V-bit is set to 1, indicating that a VCCV session message follows.
The next three bits MUST be set to 0 when sending and ignored upon
receipt. The remaining fields comprising 28 bits (i.e., Version,
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Reserved and Channel Type) follow the same definition, format and
number registry from Section 5 of [RFC4385].
Depending on the CV Type in use, the Channel Type can indicate IPv4,
IPv6 (see [RFC4385]) or BFD (see Section 8.1.3) as VCCV payload
directly following the L2SS. For CV Types of 0x01, 0x04 and 0x08,
the Channel Type can indicate IPv4 or IPv6; for CV Types of 0x10
and 0x20, the Channel Type indicates BFD Without IP/UDP Header.
6.1. L2TPv3 VCCV Message
The VCCV message over L2TPv3 directly follows the L2-Specific
Sublayer with the V-bit set. It could either contain an ICMP Echo
packet as described in Section 6.1.1, or a BFD packet as described in
Section 6.1.2.
6.1.1. L2TPv3 VCCV using ICMP Ping
When this connectivity verification mode is used, an ICMP Echo packet
[RFC792] achieves connectivity verification. The ICMP Ping packet
directly follows the L2SS with the V-bit set. In the ICMP Echo
request, the IP Header fields MUST have the following values: the
destination IP address is set to the remote LCCE's IP address for the
tunnel endpoint, the source IP address is set to the local LCCE's IP
address for the tunnel endpoint, and the TTL is set to 1.
6.1.2. L2TPv3 VCCV using BFD
The L2TPv3 Session ID provides the context to demultiplex the first
BFD control packet. See Section 4.1 and Section 4.1.1 for additional
details on BFD usage and BFD encapsulation.
6.2. L2TPv3 VCCV Capability Indication
An new optional AVP is defined in Section 6.2.1 to indicate the the
VCCV capabilities during session establishment. An LCCE MUST signal
its desire to use connectivity verification for a particular L2TPv3
session and its VCCV capabilities using the VCCV Capability AVP.
6.2.1. L2TPv3 VCCV Capability AVP
The "VCCV Capability AVP", Attribute type AVP-TBD, specifies the VCCV
capabilities as a pair of bitflags for the Control Channel (CC) and
Connectifity Verification (CV) Types. This AVP is exchanged during
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session establishment (in ICRQ, ICRP, OCRQ or OCRP messages). The
value field has the following format:
VCCV Capability AVP (ICRQ, ICRP, OCRQ, OCRP)
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CC Types | CV Types |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
CC Types:
The Control Channel (CC) Types field defines a bitmask used to
indicate the type of control channel(s) that may be used to
receive OAM traffic on for the given Session. The router agrees
to accept VCCV traffic at any time over any of the signaled VCCV
control channel types. CC Type values are defined in Section 4.
Although there is only one value defined in this document, the CC
Types field is included for forward compatibility should further
CC Types need to be defined in the future.
A CC Type of 0x01 may only be requested when there is an
L2-Specific Sublayer that defines the V-bit present. If a CC Type
of 0x01 is requested without requesting an L2-Specific Sublayer
AVP with an L2SS type that defines the V-bit, the session MUST be
disconnected with a CDN message.
If no CC Type is supported, a CC Type Indicator of 0x00 SHOULD be
sent.
CV Types:
The Connectifity Verification (CV) Types field defines a bitmask
used to indicate the specific type or types (i.e.: none, one or
more) of control packets that may be sent on the specified VCCV
control channel. CV Type values are defined in Section 4.
If no VCCV Capability AVP is signaled, then the LCCE MUST assume that
the peer is incapable of receiving VCCV and MUST NOT send any OAM
control channel traffic to it.
All L2TP AVPs have an M (Mandatory) bit, H (Hidden) bit, Length, and
Vendor ID. The Vendor ID for the VCCV Capability AVP MUST be 0,
indicating that this is an IETF-defined AVP. This AVP MAY be hidden
(the H bit MAY be 0 or 1). The M bit for this AVP SHOULD be set to
0. The Length (before hiding) of this AVP is 8.
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6.3. L2TPv3 VCCV Operation
An LCCE sends VCCV messages on an L2TPv3 signaled Pseudowire for
fault detection and diagnostic of the L2TPv3 session. The VCCV
message travels inband with the Session and follows the exact same
path as the user data for the session, because the IP header and
L2TPv3 Session header are identical. The egress LCCE of the L2TPv3
session intercepts and processes the VCCV message, and verifies the
signaling and forwarding state of the Pseudowire on reception of the
VCCV message. Any faults detected can be signaled in the VCCV
response. It is to be noted that the VCCV mechanism for L2TPv3 is
primarily targeted at verifying the Pseudowire forwarding and
signaling state at the egress LCCE. It also helps when L2TPv3 Control
Connection and Session paths are not identical.
An LCCE MUST NOT send VCCV packets on an L2TPv3 session unless it has
received VCCV capability by means of the VCCV Capability AVP from the
remote end. If an LCCE receives VCCV packets and its not VCCV
capable or it has not sent VCCV capability indication to the remote
end, it MUST discard these messages. It should also increment an
error counter. In this case the LCCE MAY optionally issue a system
and/or SNMP notification.
Additionally, because BFD is bidirectional in nature, when using BFD
as the connectivity verification type, an LCCE must send VCCV packets
on an L2TPv3 session only if it has signaled VCCV capability with a
BFD CV Type to the remote end and received VCCV capability with a
matching BFD CV Type from the remote end.
7. Capability Advertisement Preference Order
When a PE receives a VCCV capability advertisement,
the advertisement may potentially contain more than one CC or
CV Type. In this case, it MUST use the following rules when
choosing which CC or CV type to use. It may only choose one mode
based on the rules stipulated in sections 4 and 5 above. In
particular, once a valid CC Type is used by a PE (traffic
sent using that encapsulation), the PE MUST NOT send any
traffic down another CC Type encapsulation.
CC Types:
- PWE3 control word with 0001b as first nibble
- MPLS Router Alert Label
- MPLS PW Demultiplexor Label TTL = 1
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For cases were multiple CC Types are advertised,
the following precedence rules apply when choosing:
- PWE3 control word with 0001b as first nibble
- MPLS PW Demultiplexor Label TTL = 1
- MPLS Router Alert Label
The following precidence rules are used for choosing
CV Type to use:
- LSP Ping.
- BFD for PW Fault Detection only.
- ICMP Ping.
- BFD for PW Fault Detection and AC/PW Fault.
Status Signaling.
- BFD for PW Fault Detection Only. Carrying BFD payload
without IP headers.
- BFD for PW Fault Detection and AC/PW Fault
Status Signaling. Carrying BFD payload without IP headers.
8. IANA Considerations
8.1. VCCV Parameter ID
The VCCC parameter ID codepoint is defined in [RFC4446]. IANA
is requested to maintain a registry for the CC Types and CV
Types, and bitmasks in the VCCV Parameter ID. The allocations
must be done using the "First Come First Served" policy
defined in RFC2434. IANA is requested to maintain the
following registries.
8.1.1. Control Channel Types (CC Types)
IANA is requested to set up a registry of "VCCV Control Channel
Types". These are 8-bit values. CV Type values 0x01, 0x02, and 0x04
are specified in this document, PW Type values 0x08, 0x16
and 0x24 are to be assigned by IANA using the "Expert Review"
policy defined in [RFC2434]. A VCCV Control Channel Type
description is required for any assignment from this registry.
A document reference should also be provided.
0x01 Type 1: PWE3 control word with 0001b as first nibble
as defined in [RFC4385].
0x02 Type 2: MPLS Router Alert Label.
0x04 Type 3: MPLS PW Demultiplexor Label TTL = 1 (Type 3).
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8.1.2. Connectivity Verification Types (CV Types)
IANA needs to set up a registry of "VCCV Control Channel Types".
These are 8-bit values. CV Type values 0x00, 0x01, 0x02, and 0x04
are specified in this document, CV Type values 0x16
and 0x24 are to be assigned by IANA using the "Expert Review"
policy defined in [RFC2434]. A VCCV CV Type description
is required for any assignment from this registry.
A document reference should also be provided.
0x01 ICMP Ping.
0x02 LSP Ping.
0x04 BFD for PW Fault Detection Only.
0x08 BFD for PW Fault Detection and AC/PW Fault
Status Signaling.
0x10 BFD for PW Fault Detection Only. Carrying BFD payload
without IP headers.
0x20 BFD for PW Fault Detection and AC/PW Fault
Status Signaling. Carrying BFD payload without IP headers.
8.1.3 Channel Type
The Channel Types used by VCCV as defined above in section
4.1, 4.2 and 4.3 rely on previously allocated numbers
from the Pseudowire Associated Channel Types Registry
[RFC4385]. In particular, 0x21 (Internet Protocol
version 4) MUST be used whenever an IPv4 payload
follows the pseudowire control word, or 0x57 MUST be used
when an IPv6 payload follows the pseudowire control word.
In cases where raw BFD follows the pseudowire control word
(i.e.: the IP/UDP encapsulation as specified in [BFD]
will not be present), a new Pseudowire Associated Channel
Types Registry [RFC4385] entry of 0x07 is used. IANA is
requested to reserve a new Channel Types value as follows:
Value (in hex) Protocol Name Reference
-------------- ------------------------------- ---------
0007 BFD Without IP/UDP Header [This document]
8.2. L2TPv3 Assignments
Sections 8.2.1 through 8.2.3 are registrations of new L2TP values for
name spaces already managed by IANA. Section 8.2.4 requests a new
registry to be added to the existing L2TP registry, and be maintained
by IANA accordingly.
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8.2.1. Control Message Attribute Value Pairs (AVPs)
An additiona AVP Attribute is specified in Section 6.2.1. It is
required to be defined by IANA as described in Section 2.2 of
[RFC3438].
Attribute
Type Description
--------- ----------------------------------
AVP-TBD VCCV Capability AVP
8.2.2. Default L2-Specific Sublayer bits
The Default L2-Specific Sublayer contains 8 bits in the low-order
portion of the header. This document defines one reserved bits in
the Default L2-Specific Sublayer in Section 6, which may be assigned
by IETF Consensus [RFC2434]. It is required to be assigned by IANA.
Default L2-Specific Sublayer bits - per [RFC3931]
---------------------------------
Bit 0 - V (VCCV) bit
8.2.3. ATM-Specific Sublayer bits
The ATM-Specific Sublayer contains 8 bits in the low-order portion of
the header. This document defines one reserved bits in the ATM-
Specific Sublayer in Section 6, which may be assigned by IETF
Consensus [RFC2434]. It is required to be assigned by IANA.
ATM-Specific Sublayer bits - per [RFC4454]
--------------------------
Bit 0 - V (VCCV) bit
8.2.4. VCCV Capability AVP Values
This is a new registry for IANA to maintain.
IANA is requested to maintain a registry for the CC Types and CV
Types bitmasks in the VCCV Capability AVP, defined in Section 6.2.1.
The allocations must be done using the "Expert Review" policy defined
in [RFC2434]. A VCCV CC or CV Type description is required for any
assignment from this registry. A document reference should also be
provided.
IANA is requested to reserve the following bits in this registry:
VCCV Capability AVP (Attribute Type AVP-TBD) Values
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---------------------------------------------------
Control Channel (CC) Types
Bit 0 (0x01) - L2-Specific Sublayer with V-bit set.
Bit 1 (0x02) - Reserved
Bit 2 (0x04) - Reserved
Bit 3 (0x08) - Reserved
Bit 4 (0x10) - Reserved
Bit 5 (0x20) - Reserved
Bit 6 (0x40) - Reserved
Bit 7 (0x80) - Reserved
Connectifity Verification (CV) Types
Bit 0 (0x01) - ICMP Ping
Bit 1 (0x02) - Reserved
Bit 2 (0x04) - BFD for PW Fault Detection Only.
Bit 3 (0x08) - BFD for PW Fault Detection and AC/PW Fault
Status Signaling.
Bit 4 (0x10) - BFD for PW Fault Detection Only. Carrying
BFD payload without IP headers.
Bit 5 (0x20) - BFD for PW Fault Detection and AC/PW Fault
Status Signaling. Carrying BFD payload
without IP headers.
Bit 6 (0x40) - Reserved
Bit 7 (0x80) - Reserved
9. Security Considerations
Routers that implement the mechanism described herein are subject to
to additional denial-of-service attacks as follows:
An intruder may impersonate an LDP peer in order to
force a failure and reconnection of the TCP connection.
Please see the Security Considerations section of
[RFC3036] details.
An intruder could intercept or inject VCCV packets effectively
providing false positives or false negatives.
An intruder could deliberately flood a peer router with VCCV
messages to either obtain services without authorization or to
deny services to others.
A misconfigured or misbehaving device could inadvertantly flood
a peer router with VCCV messages which could result in a denial
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of services. In particular, if a router is either implicitly or
explicitly indicated that it cannot support one or all of the
types of VCCV, but is sent those messages in sufficient quantity,
could result in a denial of service.
All of attacks above which concern the L2TPv3 or LDP control planes
may be countered by use of a control message authentication scheme
between LDP or L2TPv3 peers, such as the MD5-based scheme outlined in
[RFC3036] or [RFC3931]. Implementation of IP address filters may
also aid in deterring these types of attacks.
VCCV message throttling mechanisms should be employed, especially in
distributed implementations which have a centralized control plane
processor with various line cards attached by some data path. In
these architectures VCCV messages may be processed on the central
processor after being forwarded there by the receiving line card. In
this case, the path between the line card and the control processor
may become saturated if appropriate VCCV traffic throttling is not
employed, which could lead to a denial of service. Such filtering is
also useful for preventing the processing of unwanted VCCV messages,
such as those which are sent on unwanted (and perhaps unadvertised)
control channel types or VCCV types.
VCCV spoofing requires MPLS PW label spoofing and spoofing the PSN
tunnel header. As far as the PW label is concerned the same consider-
ations as specified in [RFC3031] apply. If the PSN is a MPLS tunnel,
PSN tunnel label spoofing is also required.
10. Acknowledgements
The authors would like to thank Hari Rakotoranto, Michel Khouderchah,
Bertrand Duvivier, Vanson Lim, Chris Metz, W. Mark Townsley, Eric
Rosen, Dan Tappan, Danny McPherson and Luca Martini for their
valuable comments and suggestions.
11. References
11.1. Normative References
[RFC792] Postel, J. "Internet Control Message Protocol,
RFC792, September 1981.
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, March 1997
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC
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3031, January 2001.
[RFC3032] Rosen, E., Rehter, Y., Tappan, D., Farinacci, D.,
Fedorkow, G., Li, T. and A. Conta, "MPLS Label
Stack Encoding", RFC3032, January 2001.
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A.
and B. Thomas, "Label Distribution Protocol", RFC
3036, January 2001.
[RFC3931] J. Lau, M. Townsley, I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC3931, March 2005.
[RFC4385] Bryant, S., Martini, L., McPherson, D.,
"Pseudowire Emulation Edge-to-Edge (PWE3)
Control Word for Use over an MPLS PSN",
RFC4385, February 2006.
[RFC4446] Martini, L., "IANA Allocations for
Pseudo Wire Edge to Edge Emulation (PWE3)",
RFC4446, April 2006.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T.,
"Pseudowire Setup and Maintenance
Using the Label Distribution Protocol (LDP)",
RFC4447, April 2006.
[RFC4448] Martini, L., Rosen, E., El-Aawar, N., Heron, G.,
"Encapsulation Methods for Transport of Ethernet
over MPLS Networks", RFC4448, April 2006.
[RFC4379] Kompella, K., G. Swallow, " Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures",
RFC4379, February 2006.
[BFD] Katz, D., Ward, D., Bidirectional Forwarding
Detection", draft-ietf-bfd-05.txt, June 2006.
[IANAPPP] IANA Point-to-Point Protocol Field Assignments,
April 12, 2004,
http://www.iana.org/assignments/ppp-numbers
11.2. Informative References
[RFC4377] Nadeau, T., Swallow, G., Allan., D.,
"Operations and Management (OAM) Requirements
for Multi-Protocol Label Switched (MPLS) Networks"
RFC4377, February 2006.
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[RFC3985] Bryant, S., Pate, P., "Pseudo Wire Emulation
Edge-to-Edge Architecture", RFC 3985, March 2005.
[RFC3916] Xiao, X., McPherson, D., Pate, P., "Requirements for
Pseudo Wire Emulation Edge to-Edge (PWE3)",
RFC3916, September 2004.
[RFC2434] Narten, T. and H. Alvestrand., "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
[OAM-MAP] T. Nadeau, et. al, "Pseudo Wire (PW) OAM Message Map-
ping", draft-ietf-pwe3-oam-msg-map-03.txt,
September 2005
[RFC3036] Andersson, L, et al., "LDP Specification",
RFC3036, January 2001.
[RFC3438] Townsley, W., "Layer Two Tunneling Protocol (L2TP)
Internet Assigned Numbers Authority (IANA)
Considerations Update", BCP 68, RFC 3438,
December 2002.
[RFC4454] Singh, S., Townsley, M., Pignataro, C.,
"Asynchronous Transfer Mode (ATM) over
Layer 2 Tunneling Protocol Version 3 (L2TPv3)",
RFC4454, March 2006.
[BFDV4V61HOP] Katz, D. and D. Ward, "BFD for IPv4 and IPv6 (Single
Hop)", draft-ietf-bfd-v4v6-1hop-05, June 2006.
12. Editor Information
Thomas D. Nadeau
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, MA 01719
Email: tnadeau@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
7025 Kit Creek Road
PO Box 14987
Research Triangle Park, NC 27709
EMail: cpignata@cisco.com
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Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: rahul@juniper.net
13. Contributor Information
George Swallow
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, MA 01719
Email: swallow@cisco.com
Monique Morrow
Cisco Systems, Inc.
Glatt-com
CH-8301 Glattzentrum
Switzerland
Email: mmorrow@cisco.com
Yuichi Ikejiri
NTT Communication Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
Shinjuku-ku, JAPAN
Email: y.ikejiri@ntt.com
Kenji Kumaki
KDDI Corporation
KDDI Bldg. 2-3-2,
Nishishinjuku,
Tokyo 163-8003,
JAPAN
E-mail: ke-kumaki@kddi.com
Peter B. Busschbach
Lucent Technologies
67 Whippany Road
Whippany, NJ, 07981
E-mail: busschbach@lucent.com
Vasile Radoaca
Nortel Networks
Billerica, MA, 01803
Email: vasile@nortelnetworks.com
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14. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this specification
can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
15. Full Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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