Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Category: Standard Track
Expires: June 2007 J.P. Vasseur (Editor)
Cisco System Inc.
Yuichi Ikejiri
NTT Communications
Raymond Zhang
BT Infonet
December 2006
OSPF protocol extensions for Path Computation Element (PCE) Discovery
draft-ietf-pce-disco-proto-ospf-01.txt
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Abstract
There are various circumstances where it is highly desirable for a
Path Computation Client (PCC) to be able to dynamically and
automatically discover a set of Path Computation Element(s) (PCE),
along with some of information that can be used for PCE selection.
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When the PCE is a Label Switch Router (LSR) participating to the IGP,
or even a server participating passively to the IGP, a simple and
efficient way for PCE discovery consists of relying on IGP flooding.
For that purpose this document defines OSPF extensions for the
advertisement of PCE Discovery information within an OSPF area or
within the entire OSPF routing domain.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
Table of Contents
1. Note (to be removed before publication).....................3
2. Terminology.................................................3
3. Introduction................................................4
4. Overview....................................................5
4.1. PCE Information.............................................5
4.1.1. PCE Discovery Information...................................5
4.1.2. PCE Status Information......................................6
4.2. Flooding scope..............................................6
5. OSPF extensions.............................................6
5.1. The OSPF PCED TLV...........................................6
5.1.1. PCE-ADDRESS sub-TLV.........................................8
5.1.2. PATH-SCOPE sub-TLV..........................................8
5.1.3. PCE-DOMAINS sub-TLV........................................10
5.1.3.1. IPv4 area ID DOMAIN sub-TLV..............................11
5.1.3.2. IPv6 area ID DOMAIN sub-TLV..............................12
5.1.3.3. AS Number sub-TLV........................................12
5.1.4. PCE-DEST-DOMAINS sub-TLV...................................12
5.1.5. GENERAL-CAP sub-TLV........................................13
5.1.6. The PATH-COMP-CAP sub-TLV..................................14
5.1.6.1. Objective Functions sub-TLV..............................16
5.1.6.2. Opaque Objective Function sub-TLV........................16
5.1.6.3. Switch Caps sub-TLV......................................17
5.2. The OSPF PCES TLV..........................................17
5.2.1. The CONGESTION sub-TLV.....................................18
6. Elements of Procedure......................................19
6.1.1. PCES TLV specific procedures...............................20
7. Backward compatibility.....................................20
8. IANA considerations........................................21
8.1. OSPF TLVs..................................................21
8.2. Capability bits............................................22
9. Security Considerations....................................22
10. Manageability Considerations...............................23
11. Acknowledgments............................................23
12. References.................................................23
12.1. Normative references.......................................23
12.2. Informative references.....................................24
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13. Editor's Addresses:........................................24
14. Contributors' Addresses:...................................24
15. Intellectual Property Statement............................24
1. Note (to be removed before publication)
This document specifies new TLVs and sub-TLVs to be carried within
the OSPF Router information LSA ([OSPF-CAP]). Because this document
does not introduce any new element of procedure it will be discussed
within the PCE Working Group with a review of the OSPF Working Group.
2. Terminology
Terminology used in this document
ABR: IGP Area Border Router.
AS: Autonomous System.
Domain: any collection of network elements within a common sphere
of address management or path computational responsibility.
Examples of domains include IGP areas and Autonomous Systems.
Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries.
Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries.
Inter-area TE LSP: A TE LSP whose path transits through
two or more IGP areas.
Inter-AS TE LSP: A TE LSP whose path transits through two or more
ASes or sub-ASes (BGP confederations).
LSR: Label Switch Router.
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: an entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph, and applying computational
constraints.
PCEP: Path Computation Element Protocol.
TE LSP: Traffic Engineered Label Switched Path.
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3. Introduction
[RFC4655] describes the motivations and architecture for a PCE-based
path computation model for Multi Protocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) Traffic Engineered Label Switched Paths (TE-
LSPs). The model allows for the separation of PCE from PCC (also
referred to as non co-located PCE) and allows for cooperation between
PCEs. This relies on a communication protocol between PCC and PCE,
and between PCEs. The requirements for such communication protocol
can be found in [RFC4657] and the communication protocol is defined
in [PCEP].
The PCE architecture requires, of course, that a PCC be aware of the
location of one or more PCEs in its domain, and also potentially of
some PCEs in other domains, e.g. in case of inter-domain TE LSP
computation.
A network may comprise a large number of PCEs with potentially
distinct capabilities. In such context it is highly desirable to have
a mechanism for automatic and dynamic PCE discovery, which allows
PCCs to automatically discover a set of PCEs, along with additional
information required for PCE selection, and to dynamically detect new
PCEs or any modification of PCE information. Detailed requirements
for such a PCE discovery mechanism are described in [RFC4674].
Moreover, it may also be useful to discover when a PCE experiences
some processing congestion state and exits such state, in order for
the PCCs to take some appropriate actions (e.g. redirect to another
PCE). Note that the PCE selection algorithm is out of the scope of
this document.
When PCCs are LSRs participating to the IGP (OSPF or IS-IS), and PCEs
are LSRs or a servers also participating to the IGP, an efficient
mechanism for PCE discovery within an IGP routing domain consists of
relying on IGP advertisements.
This document defines OSPF extensions allowing a PCE in the OSPF
routing domain to advertise its location along with some information
useful for PCE selection so as to satisfy dynamic PCE discovery
requirements set forth in [RFC4674]. This document also defines
extensions allowing a PCE in the OSPF routing domain to advertise its
potential processing congestion state.
Generic capability mechanisms for OSPF have been defined in [OSPF-
CAP] the purpose of which is to allow a router to advertise its
capability within an OSPF area or an entire OSPF routing domain. Such
OSFP extensions fully satisfy the aforementioned dynamic PCE
discovery requirements.
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This document defines two new sub-TLVs (named the PCE Discovery
(PCED) TLV and the PCE Status (PCES) TLV), to be carried within the
OSPF Router Information LSA ([OSPF-CAP]).
The PCE information advertised is detailed in section 4. Protocol
extensions and procedures are defined in section 5 and 6.
This document does not define any new OSPF element of procedure but
how the procedures defined in [OSPF-CAP] should be used.
The routing extensions defined in this document allow for PCE
discovery within an OSPF Routing domain. Solutions for PCE discovery
across AS boundaries are beyond the scope of this document, and for
further study.
In this document, we call TLV any TLV that is carried within an OSPF
LSA. We call indifferently TLV or sub-TLV, any TLV that is itself
carried within another TLV.
4. Overview
4.1. PCE Information
The PCE information advertised via OSPF falls into two categories:
PCE Discovery Information and PCE Status information.
4.1.1. PCE Discovery Information
The PCE Discovery information is comprised of:
- The PCE location: an IPv4 and/or IPv6 address that must be
used to reach the PCE. It is RECOMMENDED to use addresses always
reachable;
- The PCE inter-domain functions: PCE path computation scope (i.e.
inter-area, inter-AS, inter-layer
);
- The PCE domain(s): the set of one or more domain(s) where
the PCE has visibility and can compute paths;
- The PCE Destination domain(s): set of one or more destination
domain(s) towards which a PCE can compute paths;
- A set of general PCEP capabilities (e.g. support for request
prioritization) and path computation specific capabilities
(e.g. supported constraints, supported objective functions).
Optional elements to describe more complex capabilities may also be
advertised.
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PCE Discovery information is by nature fairly static and does not
change with PCE activity. Changes in PCE Discovery information may
occur as a result of PCE configuration updates, PCE
deployment/activation, PCE deactivation/suppression or PCE failure.
Hence, this information is not expected to change frequently.
4.1.2. PCE Status Information
The PCE Status is optional information and can be used to report a
PCE processing congested state along with an estimated congestion
duration. This is a dynamic information, which may change with PCE
activity.
Procedures for a PCE to move from a processing congested state to a
non congested state are beyond the scope of this document, but the
rate at which a PCE Status change is advertised MUST not impact by
any mean the IGP scalability. Particular attention should be given on
procedures to avoid state oscillations.
4.2. Flooding scope
The flooding scope for PCE Discovery Information can be limited to
one or more OSPF areas the PCE belongs to or can be extended across
the entire OSPF routing domain.
Note that some PCEs may belong to multiple areas, in which case the
flooding scope may comprise these areas. This could be the case of an
ABR for instance advertising its PCE information within the backbone
area and/or a subset of its attached IGP area(s).
5. OSPF extensions
5.1. The OSPF PCED TLV
The OSPF PCE Discovery TLV (PCED TLV) is made of a set of non-ordered
sub-TLVs.
The format of the OSPF PCED TLV and its sub-TLVs is the identical as
the TLV format used by the Traffic Engineering Extensions to OSPF
[RFC3630]. That is, the TLV is composed of 2 octets for the type, 2
octets specifying the TLV length and a value field. The Length field
defines the length of the value portion in octets.
The TLV is padded to four-octet alignment; padding is not included in
the length field (so a three octet value would have a length of
three, but the total size of the TLV would be eight octets). Nested
TLVs are also 32-bit aligned. Unrecognized types are ignored. All
types between 32768 and 65535 are reserved for vendor-specific
extensions. All other undefined type codes are reserved for future
assignment by IANA.
The OSPF PCED TLV has the following format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value=2)
Length Variable
Value This comprises one or more sub-TLVs
Sub-TLVs types are under IANA control.
Currently five sub-TLVs are defined (type values to be assigned by
IANA):
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 4 PATH-SCOPE sub-TLV
3 variable PCE-DOMAINS sub-TLV
4 variable PCE-DEST-DOMAINS sub-TLV
5 variable GENERAL-CAP sub-TLV
6 variable PATH-COMP-CAP sub-TLV
The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within
the PCED TLV.
The PCE-DOMAINS and PCE-DEST-DOMAINS sub-TLVs are optional. They MAY
be present in the PCED TLV to facilitate selection of inter-domain
PCEs.
The GENERAL-CAP and PATH-COMP-CAP sub-TLVs are optional and MAY be
present in the PCED TLV to facilitate the PCE selection process.
Any non recognized sub-TLV MUST be silently ignored.
Additional sub-TLVs could be added in the future to advertise
additional information.
The PCED TLV is carried within an OSPF Router Information LSA
defined in [OSPF-CAP].
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5.1.1. PCE-ADDRESS sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address(es) that MUST be
used to reach the PCE. It is RECOMMENDED to make use of an address
that is always reachable, provided that the PCE is alive.
The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
PCED TLV. It MAY appear twice, when the PCE has both an IPv4 and IPv6
address. It MUST NOT appear more than once for the same address type.
The format of the PCE-ADDRESS sub-TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| address-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// PCE IP Address //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PCE-ADDRESS sub-TLV format
Type To be assigned by IANA (suggested value =1)
Length 4 (IPv4) or 16 (IPv6)
Address-type:
1 IPv4
2 IPv6
PCE IP Address: The IP address to be used to reach the PCE.
This is the address that will be used for
setting up PCC-PCE communication sessions.
5.1.2. PATH-SCOPE sub-TLV
The PATH-SCOPE sub-TLV indicates the PCE path computation scope(s),
which refers to the PCE ability to compute or take part into the
computation of intra-area, inter-area, inter-AS or inter-layer_TE
LSP(s).
The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the
PCED TLV. There MUST be exactly one instance of the PATH-SCOPE sub-
TLV within each PCED TLV.
The PATH-SCOPE sub-TLV contains a set of bit flags indicating the
supported path scopes (intra-area, inter-area, inter-AS, inter-layer)
and four fields indicating PCE preferences.
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The PATH-SCOPE sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5| Reserved |PrefL|PrefR|PrefS|PrefY| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =2)
Length Variable
Value This comprises a 2 bytes flag where each bit
represents a supported path scope, as well as four
preference fields used to specify PCE preferences.
The following bits are defined:
Bit Path Scope
0 L bit: Can compute intra-area path
1 R bit: Can act as PCE for inter-area TE LSPs
computation
2 Rd bit: Can act as a default PCE for inter-area TE LSPs
computation
3 S bit: Can act as PCE for inter-AS TE LSPs computation
4 Sd bit: Can act as a default PCE for inter-AS TE LSPs
computation
5 Y bit: Can compute or take part into the computation of
paths across layers.
Pref-L field: PCE's preference for intra-area TE LSPs computation.
Pref-R field: PCEs preference for inter-area TE LSPs computation.
Pref-S field: PCEs preference for inter-AS TE LSPs computation.
Pref-Y field: PCE's preference for inter-layer TE LSPs computation.
Res: Reserved for future usage.
The bits L, R, S and Y bits are set when the PCE can act as a PCE for
intra-area, inter-area, inter-AS and inter-layer TE LSPs computation
respectively. These bits are non exclusive.
When set the Rd bit indicates that the PCE can act as a default PCE
for inter-area TE LSPs computation (the PCE can compute path for any
destination area). Similarly, when set the Sd bit indicates that the
PCE can act as a default PCE for inter-AS TE LSPs computation (the
PCE can compute path for any destination AS).
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When the Rd bit is set the PCE-DEST-DOMAIN TLV (see 5.1.4) does not
contain any Area ID DOMAIN sub-TLV.
Similarly, when the Sd bit is set the PCE-DEST-DOMAIN TLV does not
contain any AS-DOMAIN sub-TLV.
The PrefL, PrefR, PrefS and PrefY fields are 3-bit long and allow the
PCE to specify a preference for each computation scope, where 7
reflects the highest preference. Such preference can be used for
weighted load balancing of requests. An operator may decide to
configure a preference to each PCE so as to balance the path
computation load among them, with respect to their respective CPU
capacity. The algorithms used by a PCC to load balance its path
computation requests according to such PCEs preference is out of the
scope of this document. Same or distinct preferences may be used for
different scopes. For instance an operator that wants a PCE capable
of both inter-area and inter-AS computation to be used preferably for
inter-AS computation may configure a PrefS higher than the PrefR.
When the PrefL, PrefR, PRefS or PrefY is cleared, this indicates an
absence of preference.
When the L bit, R bit, S or Y bit are cleared, the PrefL, PrefR,
PrefS, PrefY fields MUST respectively be set to 0.
5.1.3. PCE-DOMAINS sub-TLV
The PCE-DOMAINS sub-TLV specifies the set of domains (areas, AS)
where the PCE has topology visibility and can compute paths. It
contains a set of one or more sub-TLVs where each sub-TLV identifies
a domain.
The PCED TLV MUST include zero or one PCE-DOMAINS sub-TLV.
The PCE-DOMAINS sub-TLV MUST be present when PCE domains cannot be
inferred by other IGP information, for instance when the PCE is
inter-domain capable (i.e. when the R bit or S bit is set) and the
flooding scope is the entire OSPF routing domain.
The PCE-DOMAINS sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// DOMAIN sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type To be defined by IANA (suggested value =3)
Length Variable
Value This comprises a set of one or more DOMAIN sub-TLVs
where each DOMAIN sub-TLV identifies a domain where
the PCE has topology visibility and can compute paths.
Sub-TLVs types are under IANA control.
Currently three DOMAIN sub-TLVs are defined (suggested type values to
be assigned by IANA):
Sub-TLV type Length Name
1 variable IPv4 area ID sub-TLV
2 variable IPv6 area ID sub-TLV
3 variable AS number sub-TLV
The PCE-DOMAINS sub-TLV MUST include at least one DOMAIN sub-TLV.
Note than when the PCE visibility is an entire AS, the PCE-DOMAINS
sub-TLV MUST uniquely include one AS number sub-TLV.
5.1.3.1. IPv4 area ID DOMAIN sub-TLV
The IPv4 area ID DOMAIN sub-TLV carries an IPv4 OSPF area identifier.
It has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =1)
Length 4
IPv4 OSPF area ID: The IPv4 identifier of the OSPF area
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5.1.3.2. IPv6 area ID DOMAIN sub-TLV
The IPv6 area ID sub-TLV carries an IPv6 OSPF area identifier. It has
the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Area ID |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =2)
Length 16
IPv6 OSPF area ID: The IPv6 identifier of the OSPF area
5.1.3.3. AS Number sub-TLV
The AS Number sub-TLV carries an AS number. It has the following
format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =3)
Length 4
AS Number: AS number identifying an AS. When coded on two
bytes (which is the current defined format as the
time of writing this document), the AS Number field
MUST have its left two bytes set to 0.
5.1.4. PCE-DEST-DOMAINS sub-TLV
The PCE-DEST-DOMAINS sub-TLV specifies the set of destination domains
(areas, AS) toward which a PCE can compute paths. It means that the
PCE can compute or take part in the computation of inter-domain LSPs
whose destinations are located within one of these domains. It
contains a set of one or more sub-TLVs where each sub-TLV identifies
a domain.
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The PCE-DEST-DOMAINS sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// DOMAIN sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =3)
Length Variable
Value This comprises a set of one or more Area and/or AS
DOMAIN sub-TLVs where each DOMAIN sub-TLV identifies a
domain toward which a PCE can compute paths.
The PCE-DEST-DOMAINS sub-TLV MUST be present if the R bit is set and
the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is
cleared.
The PCE-DEST-DOMAINS sub-TLV MUST include at least one DOMAIN sub-
TLV. It MUST include at least one area ID sub-TLV, if the R bit of
the PATH-SCOPE TLV is set and the Rd bit of the PATH-SCOPE TLV is
cleared. Similarly, it MUST include at least one AS number sub-TLV if
the S bit of the PATH-SCOPE TLV is set and the Sd bit of the PATH-
SCOPE TLV is cleared.
5.1.5. GENERAL-CAP sub-TLV
The GENERAL-CAP sub-TLV is an optional TLV used to indicate PCEP
related capabilities. It MAY be present within the PCED TLV. It MUST
not be present more than once.
The value field of the GENERAL-CAP sub-TLV is made of a 32-bit flag,
where each bit corresponds to a general PCE capability. It MAY also
include optional sub-TLVs to encode more complex capabilities.
The format of the GENERAL-CAP sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| General Capabilities Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type To be assigned by IANA (suggested value =1)
Length Variable.
Value This comprises a 32-bit flag. The bits are indexed
from the most significant to the least significant,
where each bit represents one general PCE capability.
Optional TLVs may be added to specify more complex
capabilities: there is no optional TLV currently
defined.
IANA is requested to manage the space of the General Capabilities 32-
bit flag.
The following bits are to be assigned by IANA:
Bit Capabilities
0 P bit: Support for Request prioritization.
1 M bit: Support for multiple messages within the same
request message.
2-31 Reserved for future assignments by IANA.
5.1.6. The PATH-COMP-CAP sub-TLV
The PATH-COMP-CAP sub-TLV is an optional sub-TLV used to indicate
path computation specific capabilities. It MAY be present within the
PCED TLV. It MUST not be present more than once.
It is made of a 32-bit flag, where each bit corresponds to a path
computation capability. It MAY also include optional sub-TLVs to
encode more complex capabilities.
The format of the PATH-COMP-CAP sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Computation Capabilities Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =1)
Length Variable.
Value This comprises a 32 bit flag. Bits are indexed from
the most significant to the least significant, where
each bit represents one path computation capability.
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Optional TLVs may be defined to specify more complex
capabilities. Three optional sub-TLVs are currently
defined.
IANA is requested to manage the space of the Path Commutation
Capabilities 32-bit flag.
The following bits are to be assigned by IANA:
Bit Capabilities
0 G bit: Capability to handle GMPLS link constraints
1 B bit: Capability to compute bidirectional paths
2 D bit: Capability to compute link/node/SRLG diverse paths
3 L bit: Capability to compute load-balanced paths
4 S bit: Capability to compute a set of paths in a
synchronized Manner
5 O bit: Support for multiple objective functions
6 P bit: Capability to handle path constraints (e.g. hop
count, metric bound)
7-31 Reserved for future assignments by IANA.
The G, B, D, L, S, O and P bits are not exclusive.
Three optional sub-TLVs are currently defined for the PATH-COMP-CAP
TLV:
- The Objective Functions sub-TLV (type to be defined, suggested
value =1) that carries a list of supported objective functions,
where each objective function is identified by a 16 bit integer.
- The Opaque Objective Function sub-TLV (type to be defined,
suggested value =2) that allows the user to encode a specific
objective function in any appropriate language.
- The Switch Caps sub-TLV (type to be defined, suggested value =3)
that carries a list of supported switching capabilities. It means
that the PCE can compute path for the listed switching
capabilities.
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5.1.6.1. Objective Functions sub-TLV
The format of the Objective Functions sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| function 1 | function 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| function N | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =1)
Length Variable (N*2), where N is the number of supported
objective functions.
Value This comprises a set of one or more 16 bit function
ids, where each function id identifies a supported
objective function.
Objectives functions and their identification will be defined in a
separate document.
The Objective Functions sub-TLV is optional, it MAY be present with
the PATH-COMP-CAP TLV. When present it MUST be present only once in
the PATH-COMP-CAP TLV.
5.1.6.2. Opaque Objective Function sub-TLV
The format of the Opaque Objective Function sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque objective function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =2)
Length Variable
Value This encode a specific objective function in any
appropriate language.
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The Opaque Objective Function sub-TLV is optional. The PATH-COMP-CAP TLV
MAY comprise 0, one or more Opaque Objective Function sub-TLVs.
5.1.6.3. Switch Caps sub-TLV
The format of the Switch Caps sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC type | SC type | SC type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =3)
Length Variable = N, where N is the number of supported
switching capabilities
Value This comprises a set of one or more 8-bit switching
types, where each switching type identifies a
supported switching capability.
Switching type values are defined in [RFC4203].
The Switch Caps sub-TLV is optional, it MAY be present in the PATH-COMP-
CAP TLV. When present it MUST be present only once in the PATH-COMP-CAP
TLV.
5.2. The OSPF PCES TLV
The OSPF PCE Status TLV (PCES TLV) carries information related to PCE
processing congestion state.
The PCES TLV is carried within an OSPF Router Information LSA which
is defined in [OSPF-CAP].
The OSPF PCES TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// PCE ADDRESS sub-TLV //
// CONGESTION sub-TLV //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value=3)
Length Variable
Value This comprises a PCE ADDRESS sub-TLV, identifying the
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Internet Draft draft-ietf-pce-disco-proto-ospf-01.txt December 2006
PCE and a CONGESTION sub-TLV that contains congestion
information.
Sub-TLV types are under IANA control.
Currently two sub-TLVs are defined (type values to be assigned by
IANA):
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 4 CONGESTION sub-TLV
There MUST be exactly one occurrence of the PCE-ADDRESS and
CONGESTION sub-TLVs within a PCES TLV. The PCE-ADDRESS sub-TLV is
defined in section 5.1.1.
It carries one of the PCE IP addresses and is used to identify the
PCE experiencing a processing congestion state. This
is required as the PCES and PCED TLVs may be carried in separate
Router Information LSAs.A PCE implementation MUST use the same IP
address for the PCE-ADDRESS sub-TLV carried within the PCED TLV and
the PCE-ADDRESS TLV carried within the PCES sub-TLV.
Any non recognized sub-TLV MUST be silently ignored.
Additional sub-TLVs could be added in the future to advertise
additional congestion information.
5.2.1. The CONGESTION sub-TLV
The CONGESTION sub-TLV is used to indicate whether a PCE experiences
a processing congestion state or not along with optionally the
expected PCE congestion duration.
The CONGESTION sub-TLV is mandatory. There MUST be a single instance
of the CONGESTION sub-TLV within the PCES TLV.
The format of the CONGESTION sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Reserved | Congestion Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =2)
Length 4
Value
-C bit: When set this indicates that the PCE experiences
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Internet Draft draft-ietf-pce-disco-proto-ospf-01.txt December 2006
congestion and cannot accept any new request. When
cleared this indicates that the PCE does not
experience congestion and can accept new requests.
-Congestion Duration: 2-bytes, the estimated PCE congestion
duration in seconds.
When C is set and the Congestion Duration field is equal to 0, this
means that the Congestion Duration is unknown.
When C is cleared the Congestion Duration MUST be set to 0.
6. Elements of Procedure
The PCES and PCED TLV are advertised within an OSPFv2 Router
Information LSA (Opaque type of 4 and Opaque ID of 0) or OSPFv3
Router information LSA (function code of 12) which are defined in
[OSPF-CAP]. As such, elements of procedure are inherited
from those defined in [OSPF-CAP].
As the PCES information is likely to change more frequently than the
PCED information, it is RECOMMENDED to carry PCES and PCED TLVs in
separate Router Information LSAs, so as not to carry all PCED
information each time the PCE status changes.
In OSPFv2 the flooding scope is controlled by the opaque LSA type (as
defined in [RFC2370]) and in OSPFv3 by the S1/S2 bits (as defined in
[RFC2740]). If the flooding scope is local to an area then the PCED
or PCES TLV MUST be carried within an OSPFv2 type 10 router
information LSA or an OSPFV3 Router Information LSA with the S1 bit
set and the S2 bit cleared. If the flooding scope is the entire
domain then the PCED or PCES TLV MUST be carried within an OSPFv2
type 11 Router Information LSA or OSPFv3 Router Information LSA with
the S1 bit cleared and the S2 bit set.
When only the L bit of the PATH-SCOPE sub-TLV is set, the flooding
scope MUST be local.
Note that the flooding scope of the PCED and PCES TLVs may be
distinct, in which case they will be carried in separate LSA.
A router MUST originate a new OSPF router information LSA whenever
the content of the PCED TLV or PCES TLV changes or whenever required
by the regular OSPF procedure (LSA refresh (every LSRefreshTime)).
PCED and PCES sub-TLVs are OPTIONAL. When an OSPF LSA does not
contain any PCED or PCES sub-TLV, this means that the PCE information
of that node is unknown.
A change in PCED or PCES information MUST not trigger any
SPF computation.
The way PCEs retrieve their own information is out of the scope of
this document. Some information may be configured on the PCE (e.g.
address, preferences, scope) and other information may be
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automatically retrieved by the PCE (e.g. areas of visibility).
6.1.1. PCES TLV specific procedures
When a PCE enters into a processing congestion state, the conditions
of which are implementation dependent, it SHOULD originate a Router
Information LSA with a PCES TLV with the C bit set, and optionally a
non-null expected congestion duration.
When a PCE exits from the processing congestion state, the conditions
of which are implementation dependent, two cases are considered:
- If the congestion duration in the previously originated PCES
TLV was null, it SHOULD originate a PCES TLV with the C bit cleared
and a null congestion duration;
- If the congestion duration in the previously originated PCES
TLV was non null, it MAY originate a PCES TLV. Note that in some
particular cases it may be desired to originate a PCES TLV with the C
bit cleared if the congestion duration was over estimated.
The congestion duration allows reducing the amount of OSPF flooding,
as only uncongested-to-congested state transitions are advertised.
An implementation SHOULD support an appropriate dampening algorithm
so as to dampen OSPF flooding in order to not impact the OSPF
scalability. It is RECOMMENDED to introduce some hysteresis for
congestion state transition, so as to avoid state oscillations that
may impact OSPF performances. For instance two thresholds MAY be
configured: A resource congestion upper-threshold and a resource
congestion lower-threshold. An LSR enters the congested state when
the CPU load reaches the upper threshold and leaves the congested
state when the CPU load goes under the lower threshold.
Upon receipt of an updated PCES TLV a PCC should take appropriate
actions. In particular, the PCC SHOULD stop sending requests to a
congested PCE, and SHOULD gradually start sending again requests to a
no longer congested PCE.
7. Backward compatibility
The PCED and PCES TLVs defined in this document do not introduce any
interoperability issue.
A router not supporting the PCED/PCES TLVs will just silently ignore
the TLVs as specified in [OSPF-CAP].
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8. IANA considerations
8.1. OSPF TLVs
IANA will assign two new codepoints for the PCED and PCES sub-TLVs
carried within the Router Information LSA defined in [OSPF-CAP].
Type Description Reference
1 PCED [OSPF-CAP]
2 PCES [OSPF-CAP]
8.1.1 TLVs carried within the PCED TLV
IANA is requested to manage sub-TLV types for the PCED TLV.
Five sub-TLVs types are defined for the PCED sub-TLV and should be
assigned by IANA:
Type Description Reference
1 PCE-ADDRESS This document
2 PATH-SCOPE This document
3 PCE-DOMAINS This document
4 PCE-DEST-DOMAINS This document
5 GENERAL-CAP This document
6 PATH-COMP-CAP This document
TLVs carried within the PCE-DOMAINS and PCE-DEST-DOMAINS TLV
Three TLVs types are defined for the PCE-DOMAINS and PCE-DEST-DOMAINS
TLVs and should be assigned by IANA:
Type Description Reference
1 IPv4 Area ID This document
2 IPv6 Area ID This document
3 AS number This document
TLV carried within the PATH-COMP-CAP sub-TLV
Three sub-TLV types are defined for the PATH-COMP-CAP TLV and should
be assigned by IANA:
Type Description Reference
1 Objective Functions This document
2 Opaque Objective Function This document
3 Switch Caps sub-TLV This document
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8.1.2 TLVs carried within the PCES TLV
IANA is requested to manage TLV types for the PCES TLV.
Type Description Reference
1 PCE-ADDRESS This document
2 CONGESTION This document
8.2. Capability bits
IANA is requested to manage the space of the General Capabilities
32-bit flag and the Path Computation Capabilities 32-bit flag defined
in this document, numbering them in the usual IETF notation starting
at zero and continuing through 31.
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
- Bit number
- Defining RFC
- Name of bit
Currently two bits are defined in the General Capabilities flag. Here
are the suggested values:
-0: Support for Request prioritization.
-1: Support for multiple messages within the same request message
Currently seven bits are defined in the Path Computation Capabilities
flag. Here are the suggested values:
-0: Capability to handle GMPLS Constraints
-1: Capability to compute bidirectional paths
-2: Capability to compute link/node/SRLG diverse paths
-3: Capability to compute load-balanced paths
-4: Capability to compute a set of paths in a
synchronized Manner
-5: Support for multiple objective function
-6: Capability to handle path constraints (e.g. hop count, metric
bound)
9. Security Considerations
Any new security issues raised by the procedures in this document
depend upon the opportunity for LSAs to be snooped, the
ease/difficulty of which has not been altered. As the LSAs may now
contain additional information regarding PCE capabilities, this
new information would also become available. Mechanisms defined to
secure OSPF LSAs [RFC2154], and their TLVs, can be used to secure the
PCED and PCES TLVs as well.
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10. Manageability Considerations
Manageability considerations for PCE Discovery are addressed in
section 4.10 of [RFC4674].
11. Acknowledgments
We would like to thank Lucy Wong and Adrian Farrel for their useful
comments and suggestions.
12. References
12.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004.
[BCP79] Bradner, S., "Intellectual Property Rights in IETF
Technology", RFC 3979, March 2005.
[OSPF-v2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[OSPF-v3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, December 1999.
[RFC2370] Coltun, R., The OSPF Opaque LSA Option, RFC 2370, July
1998.
[RFC3630] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
Extensions to OSPF Version 2", RFC 3630, September 2003.
[OSPF-CAP] Lindem, A., Shen, N., Aggarwal, R., Shaffer, S., Vasseur,
J.P., "Extensions to OSPF for advertising Optional Router
Capabilities", draft-ietf-ospf-cap, work in progress.
[RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE)-based Architecture", RFC4655, August 2006.
[RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
RFC4674, October 2006.
[RFC4203] Kompella, Rekhter, " OSPF Extensions in Support of
Generalized Multi-Protocol Label Switching (GMPLS)", RFC4203, October
2005.
[RFC2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with
Digital Signatures", RFC 2154, June 1997.
Le Roux, Vasseur et al. OSPF extensions for PCE Discovery [Page 23]
Internet Draft draft-ietf-pce-disco-proto-ospf-01.txt December 2006
12.2. Informative references
[RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", RFC4657, September 2006.
[PCEP] Vasseur et al., Path Computation Element (PCE) communication
Protocol (PCEP) - Version 1, draft-ietf-pce-pcep, work in progress.
13. Editor's Addresses:
Jean-Louis Le Roux (Editor)
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@orange-ftgroup.com
Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc.
1414 Massachusetts avenue
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
14. Contributors' Addresses:
Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
JAPAN
Email: y.ikejiri@ntt.com
Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA
Email: raymond_zhang@infonet.com
15. 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.
Le Roux, Vasseur et al. OSPF extensions for PCE Discovery [Page 24]
Internet Draft draft-ietf-pce-disco-proto-ospf-01.txt December 2006
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.
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.
Copyright Statement
Copyright (C) The IETF Trust (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.
Le Roux, Vasseur et al. OSPF extensions for PCE Discovery [Page 25]
