One document matched: draft-ietf-pce-disco-proto-igp-00.txt
Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Category: Standard Track J.P. Vasseur (Editor)
Expires: May 2006 Cisco System Inc.
Yuichi Ikejiri
NTT
December 2005
IGP protocol extensions for Path Computation Element (PCE) Discovery
draft-ietf-pce-disco-proto-igp-00.txt
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Abstract
In various situations it would be highly useful 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 relevant for PCE selection. When the PCE is an 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
simple OSPF and ISIS extensions for the advertisement of PCE
Discovery information within and across IGP areas.
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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........................................................3
2. Terminology.................................................3
3. Introduction................................................4
4. PCE Discovery Information...................................5
4.1. Description.................................................5
4.2. Mandatory versus optional PCE information...................5
4.3. Flooding scope..............................................5
4.4. Frequency of change.........................................6
5. OSPF extensions.............................................6
5.1. The OSPF PCED TLV...........................................6
5.1.1. PCE-ADDRESS sub-TLV.........................................7
5.1.2. PATH-SCOPE sub-TLV..........................................8
5.1.3. PCE-DOMAINS sub-TLV.........................................9
5.1.3.1. IPv4 area ID DOMAIN sub-TLV..............................10
5.1.3.2. IPv6 area ID DOMAIN sub-TLV..............................11
5.1.3.3. AS Number sub-TLV........................................11
5.1.4. PCE-DEST-DOMAINS sub-TLV...................................11
5.1.5. The GENERAL-CAP sub-TLV....................................12
5.1.6. The PATH-COMP-CAP sub-TLV..................................13
5.2. Elements of Procedure......................................14
6. ISIS extensions............................................16
6.1. IS-IS PCED TLV format......................................16
6.1.1. PCE-ADDRESS sub-TLV........................................17
6.1.2. The PATH-SCOPE sub-TLV.....................................17
6.1.3. PCE-DOMAINS sub-TLV........................................19
6.1.3.1. Area ID DOMAIN sub-TLV...................................19
6.1.3.2. AS Number DOMAIN sub-TLV.................................19
6.1.4. PCE-DEST-DOMAINS sub-TLV...................................20
6.1.5. GENERAL-CAP sub-TLV........................................20
6.1.6. The PATH-COMP-CAP sub-TLV..................................21
6.2. Elements of procedure......................................22
7. Backward compatibility.....................................22
8. Security Considerations....................................22
9. IANA considerations........................................22
9.1. OSPF TLVs..................................................22
9.2. ISIS TLVs..................................................23
9.3. Capability bits............................................23
10. Security Considerations....................................24
11. References.................................................24
11.1. Normative references.......................................24
11.2. Informative references.....................................24
12. Authors' Addresses:........................................25
13. Intellectual Property Statement............................25
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1. Note
This document specifies new TLVs and sub-TLVs to be carried within
the OSPF Router information LSA ([OSPF-CAP]) and ISIS Router
Capability TLV ([ISIS-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 and ISIS Working Groups.
Furthermore, once stabilized, it may be decided to split the document
in two documents addressing the OSPF and ISIS aspects respectively.
2. Terminology
Terminology used in this document
LSR: Label Switch Router
TE LSP: Traffic Engineered Label Switched Path
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.
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
IGP Area: OSPF Area or ISIS level
ABR: IGP Area Border Router (OSPF ABR or ISIS L1L2 router)
AS: Autonomous System
ASBR: AS Border Router
Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries.
Inter-area TE LSP: A TE LSP whose path transits through
two or more IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits
through two or more ASes or sub-ASes (BGP confederations).
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.
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3. Introduction
[PCE-ARCH] describes the motivations and architecture for a PCE-based
path computation model for MPLS and GMPLS TE LSPs. The model allows
the separation of PCE from PCC (also referred to as non co-located
PCE) and allows cooperation between PCEs. This relies on a
communication protocol between PCC and PCE, and between PCEs, whose
generic requirements are listed in [PCE-COM-REQ].
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 path
computation.
A network may comprise a large number of PCEs with potentially
distinct capabilities. In such context it would be highly desirable
to have a mechanism for automatic and dynamic PCE discovery, which
would allow PCCs to automatically discover a set of PCEs, including
information required for PCE selection, and to dynamically detect new
PCEs or any modification of PCE information. This includes the
discovery by a PCC of a set of one or more PCEs in its domain, and
potentially in some other domains. The latter is a desirable function
in the case of inter-domain path computation for example.
Detailed requirements for such a PCE discovery mechanism are
described in [PCE-DISCO-REQ].
When PCCs are LSRs participating to the IGP (OSPF, ISIS), and PCEs
are LSRs participating to the IGP or any network servers
participating to the IGP, an efficient mechanism for PCE discovery
consists of relying on IGP advertisement.
This document defines OSPF and ISIS extensions allowing a PCE
participating to the IGP to advertise its location along with some
information useful for PCE selection so as to satisfy dynamic PCE
discovery requirements set forth in [PCE-DISC-REQ].
Generic capability mechanisms have been defined in [OSPF-CAP] and
[ISIS-CAP] for OSPF and ISIS respectively the purpose of which is to
allow a router to advertise its capability within an IGP area or an
entire routing domain. This perfectly fits with the aforementioned
dynamic PCE discovery requirements. Thus, a new TLV (named the PCE
Discovery (PCED) TLV) is defined for ISIS and OSPF to be carried
within the ISIS Capability TLV ([ISIS-CAP]) for ISIS and the OSPF
Router Information LSA ([OSPF-CAP]).
The PCE discovery information is detailed in section 3. Protocol
extensions and procedures are defined in section 4 and 5 for ISIS and
OSPF respectively. This document does not define any new OSPF or ISIS
element of procedure but how the procedures defined in [OSPF-CAP] and
[ISIS-CAP] should be used.
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The routing extensions defined in this document allow for PCE
discovery within and across IGP areas. Solutions for PCE discovery
across AS boundaries are for further study.
4. PCE Discovery Information
4.1. Description
The PCE Discovery information allows for dynamic discovery of PCEs.
This information is advertised by means of IGP advertisements by
PCE(s) participating to the IGP. It allows all PCCs participating to
the IGP to dynamically discover PCEs along with information useful
for PCE selection.
Such dynamic PCE discovery has various advantages:
- Simplified PCC configuration,
- Reduces risk of misconfiguration,
- Dynamic detection of a new PCE,
- Dynamic detection of any change in PCE information
- Dynamic detection of PCE aliveness (PCE liveness may require
additional mechanisms provided by the PCC-PCE communication
protocol)
4.2. Mandatory versus optional PCE information
The PCE Discovery information is comprised of:
- The PCE location: This is a set of one ore more IPv4 and or IPv6
addresses used to reach the PCE. These are basically loopback
addresses always reachable provided that the PCE is still alive.
- The PCE inter-domain functions: this refers to the PCE path
computation scope (i.e. inter-area, inter-AS, inter-layer…).
- The PCE domain(s): This is the set domain(s) where the PCE has
visibility and can compute paths.
- The set of destination domain(s) towards which a PCE can compute
paths.
- A set of general PCE capabilities (e.g. support for request
prioritization) and path computation specific PCE capabilities
(e.g. supported constraints, supported objective functions…)
These are two variable length sets of bits flags, where each bit
represent a given PCE capability.
4.3. Flooding scope
The PCE Discovery information can be flooded locally within the IGP
area the PCE belongs to, or globally across the entire routing
domain. Note that some PCEs may belong to multiple areas, in which
case the flooding scope can correspond to these areas. This could be
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the case of an ABR for instance that can advertise its PCE
information within the backbone area and/or a subset of its attached
IGP area(s).
4.4. Frequency of change
The rate at which PCE information is advertised must be controlled so
as to not impact by any mean the IGP scalability. Changes in PCE
information may occur as result of PCE configuration updates, PCE
deployment/activation or PCE deactivation/suppression. Hence, this
information is not expected to change frequently.
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
[OSPF-TE]. 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:
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):
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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 sub-TLVs PCE-ADDRESS and PATH SCOPE MUST always be present within
the PCED TLV.
The sub-TLVs PCE-DOMAINS and DEST-DOMAINS, MUST only be present in
some particular inter-domain cases.
The GENERAL-CAP and PATH-COMP-CAP are optional and MAY be present in
the PCED TLV to facilitate PCE selection.
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 which
is defined in [OSPF-CAP].
5.1.1. PCE-ADDRESS sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address to be used to reach
the PCE. This address will typically be a loop-back 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.
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 8 or 20
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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.
The PCE-ADDRESS sub-TLV MUST appear at least once in the PCED sub-TLV
originated by a PCE. It MAY appear multiple times, for instance when
the PCE has both an IPv4 and IPv6 address.
5.1.2. PATH-SCOPE sub-TLV
The PATH-SCOPE sub-TLV indicates the PCE path computation scope; in
other words the ability of the PCE 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 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 two fields indicating PCE preferences.
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 |PrefR|PrefS| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =3)
Length Variable
Value This comprises a 2 bytes flag where each bit
represents a supported path scope, as well as two
preference fields allowing 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
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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 field: PCE’s preference
Pref-S field: PCE’s preference for inter-AS TE LSPs computation
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, it means that it 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, it means that it can compute path for any destination
AS.
When the Rd bit is set the PCE-DEST-DOMAIN TLV (see 5.1.4) does not
comprise any Area ID DOMAIN sub-TLV.
When the Sd bit is set the PCE-DEST-DOMAIN TLV does not comprise any
AS DOMAIN sub-TLV.
The PrefR and PrefS fields are 3-bit long and allow the PCE to
specify a preference where 7 reflects the highest preference. For the
sake of illustration, consider the situation where N ABRs act as PCEs
for inter-area TE LSPs computation. An operator may decide to
configure a preference to each PCE that could be used to load balance
the path computation load with respect to their respective CPU
capacity. The algorithms used by a PCC to load balance its path
computation requests according to such PCE’s preference is out of the
scope of this document.
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 PCE-DOMAINS sub-TLV MUST only 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 the entire routing domain.
The PCE-DOMAINS sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// DOMAIN sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 TE LSP
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 path. It means that the
PCE can compute or take part in the computation of inter-domain LSPs
whose destination is located in 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 include at least one DOMAIN sub-
TLV.
The PCE-DEST-DOMAINS sub-TLV is optional. It MUST be present only 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 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, the PCE-DEST- DOMAINS sub-TLV 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. The GENERAL-CAP sub-TLV
The GENERAL-CAP sub-TLV is used to indicate general PCE capabilities.
The GENERAL-CAP sub-TLV is optional. It MAY be carried within the
PCED TLV.
The value field of the GENERAL-CAP sub-TLV is made of bit flags,
where each bit corresponds to a general PCE capability.
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 PCE Capabilities |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional sub-TLVs //
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =1)
Length It is set to N x 4 octets. N starts
from 1 and can be increased when there is a need.
Each 4 octets are referred to as a capability flag.
Value This comprises one or more capability flags.
For each 4 octets, the bits are indexed from the most
significant to the least significant, where each bit
represents one general PCE capability. When
the first 32 capabilities are defined, a new
capability flag will be used to accommodate the next
capability. Optional TLVs may be defined to specify
more complex capabilities: there is no optional TLVs
currently defined.
IANA is requested to manage the space of general PCE capability bit
flags.
The following bits in the first capability flag 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 used to indicate path computation
specific capabilities of a PCE.
The PATH-COMP-CAP sub-TLV is optional. It MAY be carried within the
PCED TLV.
This is a series of bit flags, where each bit correspond to a path
computation capability.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional sub-TLVs //
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =1)
Length It is set to N x 4 octets. N starts
from 1 and can be increased when there is a need.
Each 4 octets are referred to as a capability flag.
Value This comprises one or more capability flags.
For each 4 octets, the bits are indexed from the most
significant to the least significant, where each bit
represents one path computation PCE capability. When
the first 32 capabilities are defined, a new
capability flag will be used to accommodate the next
capability. Optional TLVs may be defined to specify
more complex capabilities: there is no optional TLVs
currently defined.
IANA is requested to manage the space of PCE path commutation
capability bit flags.
The following bits in the first capability flag are to be assigned by
IANA:
Bit Capabilities
0 M bit: Capability to compute P2P paths in MPLS-TE networks
1 G bit: Capability to compute P2P paths in GMPLS networks
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
6-31 Reserved for future assignments by IANA.
The M, G, D, L, S and O bits are not exclusive.
5.2. Elements of Procedure
The PCED TLV is carried within an OSPF Router information opaque LSA
(opaque type of 4, opaque ID of 0) which is defined in [OSPF-CAP].
A router MUST originate a new OSPF router information LSA whenever
the content of any of the carried TLVs changes or whenever
required by the regular OSPF procedure (LSA refresh (every
LSRefreshTime)).
The PCED TLV may be carried within a type 10 or 11 router information
LSA depending on the flooding scope of the PCE information.
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If the flooding scope is local to an area then it MUST be carried
within a type 10 router information LSA.
If the flooding scope is the entire domain then it MUST be carried
within type 11 router information LSA.
Note that when the L bit of the PATH-SCOPE TLV is set and the R bit
and S bit are cleared, the flooding scope MUST be local, and the PCED
TLV MUST be carried within a type 10 Router Information LSA.
PCED TLVs are OPTIONAL. When an OSPF LSA does not contain any PCED
TLV, this means that the PCE information of that node is unknown.
Note that a change in PCED information MUST not trigger normal SPF
computation.
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6. ISIS extensions
6.1. IS-IS PCED TLV format
The IS-IS PCED TLV is made of various non ordered sub-TLVs.
The format of the IS-IS PCED TLV and its sub-TLVs is the same as the
TLV format used by the Traffic Engineering Extensions to IS-IS [ISIS-
TE]. That is, the TLV is composed of 1 octet for the
type, 1 octet specifying the TLV length and a value field.
The IS-IS PCED TLV has the following format:
TYPE: To be assigned by IANA
LENGTH: Variable
VALUE: set of sub-TLVs
Sub-TLVs types are under IANA control.
Currently five sub-TLVs are defined (suggested type values to be
assigned by IANA):
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 2 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 sub-TLVs PCE-ADDRESS and PATH-SCOPE MUST always be present within
the PCED TLV.
The sub-TLVs PCE-DOMAINS and DEST-DOMAINS, MUST only be present in
some particular inter-domain cases.
The GENERAL-CAP and PATH-COMP-CAP are optional and MAY be present in
the PCED TLV to facilitate PCE selection.
Any non recognized sub-TLV MUST be silently ignored.
Additional sub-TLVs could be added in the future to advertise
additional PCE information.
The PCED TLV is carried within an ISIS CAPABILITY TLV which is
defined in [ISIS-CAP].
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6.1.1. PCE-ADDRESS sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address to be used to reach
the PCE. This address will typically be a loop-back address that is
always reachable, provided the PCE is alive.
The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
PCED TLV.
The PCE-ADDRESS sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =1)
LENGTH: 4 for IPv4 address and 16 for IPv6 address
VALUE: This comprises one octet indicating the address-type and 4
or 16 octets encoding the IPv4 or IPv6 address to be used
to reach the PCE
Address-type:
1 IPv4
2 IPv6
The PCE-ADDRESS sub-TLV MUST appear at least once in the PCED sub-LTV
originated by a PCE. It MAY appear multiple times, for instance when
the PCE has both an IPv4 and IPv6 address.
6.1.2. The PATH-SCOPE sub-TLV
The PATH-SCOPE sub-TLV indicates the PCE path computation scope; in
other words the ability of the PCE 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 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 two fields indicating PCE preferences.
The PATH-SCOPE sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =2)
LENGTH: Variable
VALUE: This comprises a one-byte flag of bits where each bit
represents a supported path scope, followed by a one-byte
preference field indicating PCE preferences.
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Here is the structure of the bits flag:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5|Res|
+-+-+-+-+-+-+-+-+
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
Here is the structure of the preference field
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|PrefR|PrefS|Res|
+-+-+-+-+-+-+-+-+
PrefR field: PCE’s preference for inter-area TE LSPs computation
PrefS field: PCE’s preference for inter-AS TE LSPs computation
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, it means that it 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, it means that it can compute path for any destination
AS.
When the Rd bit is set the PCE-DEST-DOMAINS TLV (see 6.1.4) does not
comprise any Area ID DOMAIN sub-TLV. When the Sd bit is set the PCE-
DEST-DOMAINS TLV does not comprise any AS DOMAIN sub-TLV.
The PrefR and PrefS fields are 3-bit long and allow the PCE to
specify a preference where 7 reflects the highest preference. For the
sake of illustration, consider the situation where N ABRs act as PCEs
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for inter-area TE LSPs computation. An operator may decide to
configure a preference to each PCE that could be used to load balance
the path computation load with respect to their respective CPU
capacity. The algorithms used by a PCC to load balance its path
computation requests according to such PCE’s preference is out of the
scope of this document
6.1.3. 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 PCE-DOMAINS sub-TLV MUST only 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 routing domain.
The PCE-DOMAINS sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =2)
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
DOMAIN Sub-TLVs types are under IANA control.
Currently two DOMAIN sub-TLVs are defined (suggested type values to
be assigned by IANA):
Sub-TLV type Length Name
1 variable Area ID sub-TLV
2 variable AS number sub-TLV
At least one DOMAIN sub-TLV MUST be present in the PCE-DOMAINS sub-
TLV.
6.1.3.1. Area ID DOMAIN sub-TLV
This sub-TLV carries an ISIS area ID. It has the following format
TYPE: To be assigned by IANA (Suggested value =1)
LENGTH: Variable
VALUE: This comprises a variable length ISIS area ID. This is the
combination of an Initial Domain Part (IDP) and High Order
part of the Domain Specific part (HO-DPS)
6.1.3.2. AS Number DOMAIN sub-TLV
The AS Number sub-TLV carries an AS number. It has the following
format:
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TYPE: To be assigned by IANA (Suggested value =2)
LENGTH: 4
VALUE: 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.
6.1.4. 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 path. It means that the
PCE can compute or take part in the computation of inter-domain LSPs
whose destination is located in one of these domains. It contains a
set of one or more DOMAIN sub-TLVs where each DOMAIN sub-TLV
identifies a domain.
The PCE-DEST-DOMAINS sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =2)
LENGTH: Variable
VALUE: This comprises a set of one or more Area or/and AS DOMAIN sub-
TLVs where each sub-TLV identifies a destination domain toward
which a PCE can compute path.
At least one DOMAIN sub-TLV MUST be present in the PCE-DEST-DOMAINS
sub-TLV.
The PCE-DEST-DOMAINS sub-TLV is optional. It MUST be present only 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 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, the PCE-DEST-DOMAINS sub-TLV
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.
6.1.5. GENERAL-CAP sub-TLV
The GENERAL-CAP sub-TLV is used to indicate general PCE capabilities.
The GENERAL-CAP sub-TLV is optional. It MAY be carried within the
PCED TLV.
This is a series of bits flags, where each bit corresponds to a
general PCE capability.
The GENERAL-CAP sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =4)
LENGTH: It is set to N. N starts from 1 and can be increased when
there is a need. Each octet is referred to as a
capability flag.
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VALUE: This comprises one or more general PCE capability
flags.
The following bits in the first capability flag are to be assigned by
IANA:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|P|M| Reserved |
+-+-+-+-+-+-+-+-+
P bit: Support for request prioritization.
M bit: Support for multiple messages within the same request message.
Reserved bits are for future assignment by IANA.
6.1.6. The PATH-COMP-CAP sub-TLV
The PATH-COMP-CAP sub-TLV is used to indicate path computation
specific capabilities of a PCE.
The PATH-COMP-CAP sub-TLV is optional. It MAY be carried within the
PCED TLV.
This is a series of bit flags, where each bit correspond to a path
computation capability.
The PATH-COMP-CAP sub-TLV has the following format:
TYPE: To be assigned by IANA (suggested value = 5)
LENGTH: It is set to N. N starts from 1 and can be increased
when there is a need. Each octet is referred to as a
capability flag.
VALUE: This comprises one or more Path Computation specific PCE
capability flags.
The following bits in the first capability flag are to be assigned by
IANA.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|M|G|D|L|S|0|Res|
+-+-+-+-+-+-+-+-+
M bit: Capability to compute P2P paths in MPLS-TE networks
G bit: Capability to compute P2P paths in GMPLS networks
D bit: Capability to compute link/node/SRLG diverse paths
L bit: Capability to compute load-balanced paths
S bit: Capability to compute a set of paths in a
synchronized Manner
O bit: Support for multiple objective functions
Reserved bits are for future assignment by IANA.
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6.2. Elements of procedure
The PCED TLV is carried within an IS-IS CAPABILITY TLV defined in
[IS-IS-CAP].
An IS-IS router MUST originate a new IS-IS LSP whenever the content
of any of the PCED TLV changes or whenever required by the regular
IS-IS procedure (LSP refresh).
When the scope of the PCED TLV is area local it MUST be carried
within an ISIS CAPABILITY TLV having the S bit cleared.
When the scope of the PCED TLV is the entire domain, the PCED TLV
MUST be carried within an ISIS CAPABILITY TLV having the S bit set.
Note that when the L bit of the PATH-SCOPE sub-TLV is set and the R
and S bits are cleared the flooding scope MUST be local.
PCED TLVs are OPTIONAL. When an IS-IS LSP does not contain any PCED
TLV, this means that the PCE information of that node is unknown.
Note that a change in PCED information MUST not trigger normal SPF
computation.
7. Backward compatibility
The PCED TLVs defined in this document do not introduce any
interoperability issue. For OSPF, a router not supporting the PCED
TLV SHOULD just silently ignore the TLV as specified in RFC2370. For
IS-IS a router not supporting the PCED TLV SHOULD just silently
ignore the TLV.
8. Security Considerations
No new security issues are raised in this document.
9. IANA considerations
9.1. OSPF TLVs
IANA will assign a new codepoint for the OSPF PCED TLV defined in
this document and carried within the Router Information LSA.
Five sub-TLVs types are defined for this TLV and should be assigned
by IANA:
-PCE-ADDRESS sub-TLV (suggested value = 1)
-PATH-SCOPE sub-TLV (suggested value = 2)
-PCE-DOMAINS sub-TLV (suggested value = 3)
-PCE-DEST-DOMAINS sub-TLV (suggested value =4)
-GENERAL-CAP sub-TLV (suggested value = 5)
-PATH-COMP-CAP sub-TLV (suggested value = 6)
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Three sub-TLVs types are defined for the PCE-DOMAINS and PCE-DEST-
DOMAINS TLVs and should be assigned by IANA:
-IPv4 area ID sub-TLV (suggested value = 1)
-IPv6 area ID sub-TLV (suggested value = 2)
-AS number sub-TLV (suggested value = 3)
9.2. ISIS TLVs
IANA will assign a new codepoint for the PCED TLV defined in this
document and carried within the ISIS CAPABILITY TLV.
Five sub-TLVs types are defined for the PCED TLV and should be
assigned by IANA:
-PCE-ADDRESS sub-TLV (suggested value = 1)
-PATH-SCOPE sub-TLV (suggested value = 2)
-PCE-DOMAINS sub-TLV (suggested value = 3)
-GENERAL-CAP sub-TLV (suggested value = 4)
-PATH-COMP-CAP sub-TLV (suggested value = 5)
Two sub-TLVs types are defined for the PCE-DOMAINS and PCE-DEST-
DOMAINS TLVs and should be assigned by IANA:
-Area ID sub-TLV (suggested value = 1)
-AS number sub-TLV (suggested value = 2)
9.3. Capability bits
IANA is requested to manage the space of general and path computation
specific PCE capability bits flags, numbering them in the usual IETF
notation starting at zero and continuing at least 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 first general PCE capability
flag. Here are the suggested values:
-0: Support for Request prioritization.
-1: Support for multiple messages within the same request message
Currently six bits are defined in the first path computation specific
PCE capability flag. Here are the suggested values:
-0: Capability to compute P2P paths in MPLS-TE networks
-1: Capability to compute P2P paths in GMPLS networks
-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 functions
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10. Security Considerations
No new security issues are raised in this document.
11. References
11.1. Normative references
[OSPF-v2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[IS-IS] "Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol " ISO 10589.
[IS-IS-IP] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[OSPF-TE] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
Extensions to OSPF Version 2", RFC 3630, September 2003.
[IS-IS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
Engineering", RFC 3784, June 2004.
[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.
[IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising
router information", draft-ietf-isis-caps, work in progress.
[PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE) Architecture", draft-ietf-pce-architecture, work in
progress.
[PCE-DISCO-REQ] Le Roux, J.L., et al. "Requirements for PCE
discovery", draft-ietf-pce-discovery-reqs, work in progress
11.2. Informative 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.
[RFC3668] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
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[PCE-COM-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs, work in
progress.
12. Authors' Addresses:
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@francetelecom.com
Jean-Philippe Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
JAPAN
Email: y.ikejiri@ntt.com
13. Intellectual Property Statement
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pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
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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
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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.
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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 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 Internet Society (2005). 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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| PAFTECH AB 2003-2026 | 2026-04-22 23:16:18 |