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Network Working Group E. Oki
Internet Draft NTT
Category: Standards Track A. Farrel
Expires: January 2008 Old Dog Consulting

July 2007

Extensions to the Path Computation Element Communication Protocol
(PCEP) for Route Exclusions

draft-ietf-pce-pcep-xro-01.txt

Status of this Memo

By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
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Abstract

The Path Computation Element (PCE) provides functions of path
computation in support of traffic engineering in Multi-Protocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) networks.

When a Path Computation Client (PCC) requests a PCE for a route, it
may be useful for the PCC to specify, as constraints to the path
computation abstract nodes, resources, and Shared Risk Link Groups
(SRLGs) that are to be explicitly excluded from the computed route.
Such constraints are termed route exclusions.

The PCE Communication Protocol (PCEP) is designed as a communication
protocol between PCCs and PCEs. This document presents PCEP
extensions for route exclusions.

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
[RFC2119].

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Table of Contents

1. Introduction...................................................2
2. Protocol Procedures and Extensions.............................3
2.1. Exclude Route Object (XRO)..................................3
2.1.1. Definition................................................3
2.1.2. Processing Rules..........................................7
2.2. Explicit Route Exclusion....................................8
2.2.1. Definition..................................................8
2.2.2. Processing Rules............................................8
3. Exclude Route with Confidentiality.............................9
3.1. Exclude Route Object (XRO) carrying Path Key................9
3.3.1. Definition..................................................9
3.3.2. Processing Rules...........................................10
4. IANA Considerations...........................................10
4.1. PCEP Objects...............................................10
4.2. Error Object Field Values..................................11
5. Manageability considerations..................................11
6. Security Considerations.......................................11
7. References....................................................11
7.1. Normative Reference........................................11
7.2. Informative Reference......................................12
8. Acknowledgements..............................................12
9. AuthorsEAddresses............................................12
10. Intellectual Property Statement.............................12

1. Introduction

The Path Computation Element (PCE) defined in [RFC4655] is an entity
that is capable of computing a network path or route based on a
network graph, and applying computational constraints. A Path
Computation Client (PCC) may make requests to a PCE for paths to be
computed.

When a PCC requests a PCE for a route, it may be useful for the PCC
to specify abstract nodes, resources, and Shared Risk Link Groups
(SRLGs) that are to be explicitly excluded from the route.

For example, disjoint paths for inter-domain LSPs may be computed by
cooperation between PCEs, each of which computes segments of the
paths across one domain. In order to achieve path computation for a
secondary (backup) path, a PCE may act as a PCC to request another
PCE for a route that must be a node/link/SRLG disjoint from the
primary (working) path. Another example is where a network operator
wants a path to avoid specified nodes for administrative reasons,
perhaps because the specified nodes will be out-of-services in the
near future.

[RFC4657] specifies generic requirements for a communication
protocol between PCCs and PCEs. Generic constraints described in
[RFC4657] include route exclusions for links, nodes, and SRLGs. That
is, the requirement for support of route exclusions within the PCC-
PCE communication protocol is already established.

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The PCE communication protocol (PCEP) is designed as a communication
protocol between PCCs and PCEs and is defined in [PCEP]. This
document presents PCEP extensions to satisfy the requirements for
route exclusions as described in Sections 5.1.4 and 5.1.16 of
[RFC4657].

Note that MPLS-TE and GMPLS signaling extensions for communicating
route exclusions between network nodes for specific Label Switched
Paths (LSPs) are described in [RFC4874]. Route exclusions may be
specified during provisioning requests for specific LSPs setting the
mplsTunnelHopInclude object of MPLS-TE-STD-MIB defined in [RFC3812]
to false.

2. Protocol Procedures and Extensions

This section describes the procedures adopted by a PCE handling a
request for path computation with route exclusions received from a
PCC, and defines how those exclusions are encoded.

There are two types of route exclusion described in [RFC4874].

1. Exclusion of certain abstract nodes or resources on the whole
path. This set of abstract nodes is referred to as the Exclude
Route List.

2. Exclusion of certain abstract nodes or resources between a
specific pair of abstract nodes present in an explicit path. Such
specific exclusions are referred to as an Explicit Route
Exclusion.

This document defines protocol extensions to allow a PCC to specify
both types of route exclusions to a PCE on a path computation
request.

A new PCEP object is defined as the Exclude Route Object (XRO) to
convey the Exclude Route List. The existing Include Route Object
(IRO) in PCEP [PCEP] is modified by introducing a new IRO subobject,
the Explicit Exclusion Route Subobject (EXRS), to convey Explicit
Route Exclusions.

2.1. Exclude Route Object (XRO)

2.1.1. Definition

The XRO is OPTIONAL and MAY be carried within PCReq and PCRep
messages.

When present in a PCReq message, the XRO provides a list of network
resources that the PCE is requested to exclude from the path that it
computes. Flags associated with each list member instruct the PCE as
to whether the network resources must be excluded from the computed
path or whether the PCE should make best efforts to exclude the
resources from the computed path.

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The XRO MAY be used on PCRep message with the NO-PATH object to
indicate the set of elements of the original XRO that prevented the
PCE from finding a path. The XRO MAY also be used on a PCRep message
for a successful path computation when the PCE wishes to provide a
set of exclusions to be signaled during LSP setup using the
extensions to RSVP-TE [RFC4874].

The XRO Object-Class is to be assigned by IANA (recommended
value=17)

The XRO Object-Type is to be assigned by IANA (recommended value=1)

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |F|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Subobjects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: XRO body format

Flags: 16 bits - The following flags are currently defined:

F (Fail - 1 bit): when set, the requesting PCC requires the
computation of a new path for an existing TE LSP that has failed. If
the F bit is set, the path of the existing TE LSP MUST be provided
in the PCReq message by means of an RRO object defined in [PCEP].
This allows the path computation to take into account the previous
path and reserved resources to avoid double bandwidth booking should
the TED have not yet been updated or the corresponding resources not
be yet been released. This will usually be used in conjunction with
the exclusion from the path computation of the failed resource that
caused the LSP to fail.

Subobjects. The XRO is up made of one or more subobject(s). An XRO
with no subobjects MUST NOT be sent and SHOULD be ignored on receipt.

In the following subobject definitions a set of fields have
consistent meaning as follows:

X
The X-bit indicates whether the exclusion is mandatory or
desired. 0 indicates that the resource specified MUST be
excluded from the path computed by the PCE. 1 indicates that
the resource specified SHOULD be excluded from the path
computed by the PCE, but MAY be included subject to PCE policy
and the absence of a viable path that meets the other
constraints and excludes the resource.

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Type
The type of the subobject. The following subobject types are
defined.

Type Subobject
-------------+-------------------------------
1 IPv4 prefix
2 IPv6 prefix
3 Unnumbered Interface ID
4 Autonomous system number
5 SRLG

Length
The length of the subobject including the Type and Length
fields.

Prefix Length
Where present, this field can be used to indicate a set of
addresses matching a prefix. If the subobject indicates a
single address, the prefix length MUST be set to the full
length of the address.

Attribute
The Attribute field indicates how the exclusion subobject is to
be interpreted.

0 Interface
The subobject is to be interpreted as an interface or set of
interfaces. All interfaces identified by the subobject are to
be excluded from the computed path according to the setting
of the X-bit. This value is valid only for subobject types 1,
2, and 3.

1 Node
The subobject is to be interpreted as a node or set of nodes.
All nodes identified by the subobject are to be excluded from
the computed path according to the setting of the X-bit. This
value is valid only for subobject types 1, 2, 3, and 4.

2 SRLG
The subobject identifies an SRLG explicitly or indicates all
of the SRLGs associated with the resource or resources
identified by the subobject. Resources that share any SRLG
with those identified are to be excluded from the computed
path according to the setting
of the X-bit. This value is valid for all subobjects.

Reserved
Reserved fields MUST be transmitted as zero and SHOULD be
ignored on receipt.

The subobjects are encoded as follows:

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IPv4 prefix Subobject

IPv6 prefix Subobject

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type = 2 | Length | IPv6 address (16 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (continued) | Prefix Length | Attribute |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unnumbered Interface ID Subobject

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type = 3 | Length | Reserved | Attribute |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The TE Router ID and Interface ID fields are as defined in
[RFC3477].

Autonomous System Number Subobject

If a two-octet AS number is used, the optional AS Number High
Octets MUST be set to zero.

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SRLG Subobject

The Attribute SHOULD be set to two (2) and SHOULD be ignored on
receipt.

2.1.2. Processing Rules

A PCC builds an XRO to encode all of the resources that it wishes
the PCE to exclude from the path that it is requested to compute.
For each exclusion, the PCC clears the X-bit to indicate that the
PCE is required to exclude the resources, or sets the X-bit to
indicate that the PCC simply desires that the resources are excluded.
For each exclusion, the PCC also sets the Attribute field to
indicate how the PCE should interpret the contents of the exclusion
subobject.

When a PCE receives a PCReq message it looks for an XRO to see if
exclusions are required. If the PCE finds more than one XRO it MUST
use the first one in the message and MUST ignore subsequent
instances.

If the PCE does not recognize the XRO it MUST return a PCErr message
with Error-Type "Unknown Object" as described in [PCEP].

If the PCE is unwilling on unable to process the XRO it MUST return
a PCErr message with the Error-Type "Not supported object" and
follow the relevant procedures described in [PCEP].

If the PCE processes the XRO and attempts to compute a path, it MUST
adhere to the requested exclusions as expressed in the XRO. That is,
the returned path MUST NOT include any resources encoded with the X-
bit clear, and SHOULD NOT include any with the X-bit set unless
alternate paths that match the other constraints expressed in the
PCReq are unavailable.

When a PCE returns a path in a PCRep it MAY also supply an XRO. An
XRO in a PCRep message with the NO-PATH object indicates that the
set of elements of the original XRO prevented the PCE from finding a
path. On the other hand, if an XRO is present in a PCRep message
without a NO-PATH object, the PCC SHOULD apply the contents using
the same rules as in [RFC4874] and the PCC or a corresponding LSR
SHOULD signal an RSVP-TE XRO to indicate the exclusions that
downstream LSRs should apply. This may be particularly useful in
per-domain path computation scenarios.

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In the event that no suitable path can be computed and the PCE
returns a PCRep message containing a NO-PATH object, the PCE MAY
also include an XRO that lists one or more subobjects from the
original XRO that have contributed to the PCE's inability to select
a path.

2.2. Explicit Route Exclusion

2.2.1. Definition
Explicit Route Exclusion defines network elements that must not or
should not be used on the path between two abstract nodes or
resources explicitly indicated in the Include Route Object (IRO)
[PCEP]. This information is encoded by defining a new subobject for
the IRO.

The new IRO subobject, the Explicit Exclusion Route Subobject (EXRS),
has type defined by IANA (see Section 3.). The EXRS contains one or
more subobjects in its own right. An EXRS MUST NOT be sent with no
subobjects, and if received with no subobjects MUST be ignored.

The format of the EXRS 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// One or more EXRS subobjects //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

L
MUST be set to zero on transmission and MUST be ignored on
receipt.

Reserved
MUST be set to zero on transmission and MUST be ignored on
receipt.

The EXRS subobject may carry any of the subobjects defined for
inclusion in the XRO by this document or by future documents. The
meanings of the fields of the XRO subobjects are unchanged when the
subobjects are included in an EXRS, except that scope of the
exclusion is limited to the single hop between the previous and
subsequent elements in the IRO.

2.2.2. Processing Rules

A PCC that supplies a partial explicit route to a PCE in an IRO MAY
also specify explicit exclusions by including one or more EXRSes in
the IRO.

If a PCE parses an IRO in a received PCReq message and encounters an
EXRS and does not recognize the subobject it MUST respond with a
PCErr message using the Error-Type "Unrecognized IRO subobject" and
set the Error-Value to the subobject type code of the EXRS (see
Section 3).

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If a PCE parses an IRO and encounters an EXRS that it recognizes,
but detects an EXRS subobject that it does not recognize it MUST act
according to the setting of the X-bit in the subobject. If the X-bit
is clear, the PCE MUST respond with a PCErr with Error-Type
"Unrecognized EXRS subobject" and set the Error-Value to the EXRS
subobject type code (see Section 3). If the X-bit is set, the PCE
MAY respond with a PCErr as already stated or MAY ignore the EXRS
subobject: this choice is a local policy decision.

If a PCE parses an IRO and encounters an EXRS subobject that it
recognizes, it MUST act according to the requirements expressed in
the subobject. That is, if the X-bit is clear, the PCE MUST NOT
produce a path that includes any resource identified by the EXRS
subobject in the path between the previous abstract node in the IRO
and the next abstract node in the IRO. If the X-bit is set, the PCE
SHOULD NOT produce a path that includes any resource identified by
the EXRS subobject in the path between the previous abstract node in
the IRO and the next abstract node in the IRO unless it is not
possible to construct a path that avoids that resource while still
complying with the other constraints expressed in the PCReq message.

A successful path computation reported in a PCRep message MUST
include an ERO to specify the path that has been computed. That ERO
MAY contain specific route exclusions using the EXRS as specified in
[RFC4874].

If the path computation fails and a PCErr is returned with a NO-PATH
object, the PCE MAY include an IRO to report the hops that could not
be complied with, and that IRO MAY include EXRSes.

3. Exclude Route with Confidentiality

3.1. Exclude Route Object (XRO) carrying Path Key

3.3.1. Definition

In PCE-based inter-domain diverse path computation, an XRO may be
used to find a backup (secondary) path. A sequential path
computation approach may be applied for this purpose, where a
working (primary) path route is computed first and a backup path
route that must be a node/link/SRLG disjoint route from the working
path is then computed [INTER-DOMAIN-REC-ANA]. Backward Recursive
Path Computation (BRPC) may be used for inter-domain path
computation [BRPC].

In some cases of inter-domain computation (e.g., where domains are
administered by different service providers), confidentiality must
be kept. For primary path computation, to preserve confidentiality,
instead of explicitly expressing the computed route, Path Key
Subobjects (PKSs) [PCE-PATH-KEY] are carried in the Explicit Route
Object (ERO) in the PCRep Message.

Therefore, during inter-domain diverse path computation, it may be
necessary to request diversity from a path that is not fully known
and where a segment of the path is represented by a PKS. This means
that a PKS may be present as a subobject of the XRO on a PCReq
message.

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The format and definition of PKS when it appears as an XRO subobject
are as defined in [PCE-PATH-KEY], except for the definition of L bit.
The L bit of the PKS subobject in the XRO is defined as follows.

L
The L bit MUST be ignored.

3.3.2. Processing Rules

Consider that BRPC is applied for both working and backup path
computation in a sequential manner. First, PCC requests PCE for the
computation of a working path. After BRPC processing has completed,
the PCC receives the results of the working-path computation
expressed in an ERO in a PCRep message. The ERO may include PKSs if
certain segments of the path are to be kept confidential.

For backup path computation, when the PCC constructs a PCReq Message,
it includes the entire working-path in the XRO so that the computed
path is node/link disjoint from the working path. The XRO may also
include SRLGs to ensure SRLG diversity from the working path. If the
working path ERO includes PKS subobjects, these are also included in
the XRO to allow the PCE to ensure diversity.

A set of PCEs for backup path computation may be the same as ones
for working path computation, or they may be different.

- Identical PCEs

In the case where the same PCEs are used for both path
computations, the processing is as follows. During the process of
BRPC for backup path computation, a PCE may encounter a PKS as it
processes the XRO when it creates a virtual path tree (VPT) in its
own domain. The PCE retrieves the PCE-ID from the PKS, recognizes
itself, and converts the PKS into a set of XRO subobjects which it
uses for the local calculation to create the VPT. The XRO subobjects
created in this way MUST NOT be shared with other PCEs. Other
operations are the same as BRPC.

- Different PCEs

In the case where a set of PCEs for bakup path computation is
different from the ones used for working path computation, the
processing is as follows. If a PCE encounters a PKS in an XRO when
it is creating a virtual path tree in its own domain, the PCE
retrieves the PCE-ID from the PKS and sends a PCReq message to the
identified PCE to expand the PKS. The PCE computing the VPT treats
the path segment in the response as a set of XRO subobjects in
performing its path computation. The XRO subobjects determined in
this way MUST NOT be shared with other PCEs.

4. IANA Considerations

4.1. PCEP Objects

The "PCEP Parameters" registry contains a subregistry "PCEP Objects".
IANA is requested to make the following allocations from this
registry.

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Object Name Object Name
Class Type
17 XRO 1 Route exclusion

4.2. Error Object Field Values.

The "PCEP Parameters" registry contains a subregistry "PCEP Errors".
IANA is requested to make the following allocations from this
registry.

Values in this section are recommended and to be confirmed by IANA.

Error Meaning and Error-Values
Type

11 Unrecognized IRO subobject
Note that this Error-Type has been omitted from [PCEP] where it is
required. It is expected that it will be added to a later version of
[PCEP] and removed from this document.

12 Unrecognized EXRS subobject

5. Manageability considerations

A MIB module for management of the PCEP is specified in a separate
document. This MIB module allows examination of individual PCEP
messages, in particular requests, responses and errors.

The MIB module MUST be extended to include the ability to view the
route exclusion extensions defined in this document.

6. Security Considerations

The new exclude route mechanisms defined in this document allow
finer and more specific control of the path computed by a PCE. Such
control increases the risk if a PCEP message is intercepted,
modified, or spoofed. Therefore, the security techniques described
in [PCEP] are considered more important.

7. References

7.1. Normative Reference

[RFC2119] Bradner, S., "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.

[PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
(work in progress).

[INTER-DOMAIN-REC-ANA] T. Takeda et al., "Analysis of Inter-domain
Label Switched Path (LSP) Recovery" draft-ietf-ccamp-inter-domain-
recovery-analysis (work in progress).

[PCE-PATH-KEY] R. Bradford, JP Vasseur, and A. Farrel, "Preserving
Topology Confidentiality in Inter-Domain Path Computation using a
key based mechanism", draft-ietf-pce-path-key (work in progress).

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[BRPC] JP. Vasseur et al, "A Backward Recursive PCE-based
Computation (BRPC) procedure to compute shortest inter-domain
Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc
(work in progress).

7.2. Informative Reference

[RFC3477] K. Kompella and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)",
RFC 3477, January 2003.

[RFC3812] Srinivasan, C., Viswanathan, A., and T. Nadeau,
"Multiprotocol Label Switching (MPLS) Traffic Engineering (TE)
Management Information Base (MIB)", RFC 3812, June 2004.

[RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, September 2006.

[RFC4657] J. Ash and J.L. Le Roux, "Path Computation Element (PCE)
Communication Protocol Generic Requirements", RFC 4657, September
2006.

[RFC4874] Lee et al, "Exclude Routes - Extension to Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)", RFC 4874, April
2007.

8. Acknowledgements

Authors would like to thank Tomonori Takeda for valuable comments on
inter-domain path computation.

9. Authors' Addresses

Eiji Oki
NTT
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: oki.eiji@lab.ntt.co.jp

Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk

10. 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.

Oki and Farrel Expires January 2008 12 Extensions to PCEP for Route Exclusions July 2007

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.

Disclaimer of Validity

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, THE
IETF TRUST 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.

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.

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