Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Category: Standard Track
Expires: August 2007 J.P. Vasseur (Editor)
Cisco System Inc.
Yuichi Ikejiri
NTT Communications
Raymond Zhang
BT Infonet
February 2007
OSPF protocol extensions for Path Computation Element (PCE) Discovery
draft-ietf-pce-disco-proto-ospf-02.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 Elements (PCE),
along with some of information that can be used for PCE selection.
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When the PCE is a Label Switching Router (LSR) participating in the
Interior Gateway Protocol (IGP), or even a server participating
passively in the IGP, a simple and efficient way to discover PCEs
consists of using IGP flooding. For that purpose, this document
defines extensions to the Open Shortest Path First (OSPF) routing
protocol 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. Terminology.................................................3
2. Introduction................................................4
3. Overview....................................................5
3.1. PCE Information.............................................5
3.2. PCE Discovery Information...................................5
3.2.1. PCE Status Information......................................6
3.3. Flooding scope..............................................6
4. OSPF extensions.............................................6
4.1. The OSPF PCED TLV...........................................6
4.1.1. PCE-ADDRESS sub-TLV.........................................8
4.1.2. PATH-SCOPE sub-TLV..........................................8
4.1.3. PCE-DOMAINS sub-TLV........................................10
4.1.3.1. Area ID DOMAIN sub-TLV...................................11
4.1.3.2. AS Number sub-TLV........................................12
4.1.4. PCE-NEIG-DOMAINS sub-TLV...................................12
4.1.5. PCE-CAP-FLAGS sub-TLV......................................13
4.1.6. The CONGESTION sub-TLV.....................................14
5. Elements of Procedure......................................15
5.1. CONGESTION sub-TLV specific procedures.....................16
6. Backward compatibility.....................................16
7. IANA Considerations........................................17
7.1. OSPF TLV...................................................17
7.2. PCED sub-TLVs registry.....................................17
7.3. PCE Capability Flags registry..............................17
8. Security Considerations....................................18
9. Manageability Considerations...............................18
9.1. Control of Policy and Functions............................18
9.2. Information and Data Model.................................19
9.3. Liveness Detection and Monitoring..........................19
9.4. Verify Correct Operations..................................19
9.5. Requirements on Other Protocols and Functional
Components...............................................19
9.6. Impact on network operations...............................19
10. Acknowledgments............................................20
11. References.................................................20
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11.1. Normative references........................................20
11.2. Informative references......................................20
12. Editor's Addresses:.........................................21
13. Contributors' Addresses:....................................21
14. Intellectual Property Statement.............................21
1. 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.
IGP: Interior Gateway Protocol. Either of the two routing
protocols Open Shortest Path First (OSPF) or Intermediate System
to Intermediate System (ISIS).
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 two or more IGP
areas. That is a TE-LSP that crosses at least one IGP area
boundary.
Inter-AS TE LSP: A TE LSP whose path transits two or more
ASes or sub-ASes (BGP confederations). That is a TE-LSP that
crosses at least one AS boundary.
LSA: Link State Advertisement
LSR: Label Switching 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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2. 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 the PCE from a PCC
(also referred to as a 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 a communication
protocol can be found in [RFC4657] and the communication protocol is
defined in [PCEP].
The PCE architecture requires 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 contain a large number of PCEs with potentially
distinct capabilities. In such a 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 about each PCE that may be required for the
PCC to perform PCE selection. Additionally, it is valuable for a PCC
to dynamically detect new PCEs or any modification of the PCE
information. Detailed requirements for such a PCE discovery mechanism
are provided in [RFC4674].
Moreover, it may also be useful to discover when a PCE experiences
processing congestion and when it exits such a state, in order for
the PCCs to take some appropriate actions (e.g. to redirect their
requests to another PCE). Note that the PCE selection algorithm
applied by a PCC is out of the scope of this document.
When PCCs are LSRs participating in the IGP (OSPF or IS-IS), and PCEs
are either LSRs or servers also participating in the IGP, an
effective mechanism for PCE discovery within an IGP routing domain
consists of utilizing IGP advertisements.
This document defines OSPF extensions to allow a PCE in an OSPF
routing domain to advertise its location along with some information
useful to a PCC for PCE selection so as to satisfy dynamic PCE
discovery requirements set forth in [RFC4674]. This document also
defines extensions allowing a PCE in an OSPF routing domain to
advertise its processing congestion state.
Generic capability advertisement mechanisms for OSPF are defined in
[OSPF-CAP]. These allow a router to advertise its capabilities within
an OSPF area or an entire OSPF routing domain. This document
leverages this generic capability advertisement mechanism to fully
satisfy the aforementioned dynamic PCE discovery requirements.
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This document defines a new sub-TLV (named the PCE Discovery (PCED)
TLV) to be carried within the OSPF Router Information LSA ([OSPF-
CAP]).
The PCE information advertised is detailed in section 3. Protocol
extensions and procedures are defined in section 4 and 5.
This document does not define any new OSPF elements of procedure. The
procedures defined in [OSPF-CAP] should be used.
The OSPF 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. Any TLV that is itself carried within another TLV is referred to
as either a TLV or a sub-TLV.
3. Overview
3.1. PCE Information
The PCE information advertised via OSPF falls into two categories:
PCE Discovery information and PCE Status information.
3.2. PCE Discovery Information
The PCE Discovery information is comprised of:
- The PCE location: an IPv4 and/or IPv6 address that is used to reach
the PCE. It is RECOMMENDED to use an address that is always
reachable;
- The PCE inter-domain functions: PCE path computation scope (e.g.,
inter-area, inter-AS, inter-layer);
- The PCE domain(s): the set of one or more domain(s) into which
the PCE has visibility and can compute paths;
- The PCE neighbor domain(s): set of one or more neighbors domain(s)
towards which a PCE can compute paths;
- A set of communication capabilities (e.g., support for request
prioritization) and path computation specific capabilities
(e.g. supported constraints).
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.
3.2.1. PCE Status Information
The PCE Status is optional information and can be used to report a
PCE's processing congestion 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 congestion state to a
non congestion state are beyond the scope of this document, but the
rate at which a PCE Status change is advertised MUST NOT impact by
any means the IGP scalability. Particular attention MUST be given to
procedures to avoid state oscillations.
3.3. Flooding scope
The flooding scope for PCE information advertised through OSPF 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 for
an ABR for instance advertising its PCE information within the
backbone area and/or a subset of its attached IGP area(s).
4. OSPF extensions
4.1. 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 identical to 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 four-octet aligned. Unrecognized types are ignored.
All Type values between 32768 and 65535 are reserved for vendor-
specific extensions. All other undefined Type codes are reserved for
future assignment by IANA.
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The OSPF PCED TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value=5)
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-NEIG-DOMAINS sub-TLV
5 variable PCE-CAP-FLAGS sub-TLV
6 4 CONGESTION sub-TLV
The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within
the PCED TLV.
The PCE-DOMAINS and PCE-NEIG-DOMAINS sub-TLVs are optional. They MAY
be present in the PCED TLV to facilitate selection of inter-domain
PCEs.
The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED
TLV to facilitate the PCE selection process.
The CONGESTION sub-TLV is optional and MAY be present in the PCED
TLV, to indicate a PCE's processing congestion state.
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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4.1.1. PCE-ADDRESS sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address(es) that can 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:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| address-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// PCE IP Address //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PCE-ADDRESS sub-TLV format
Type To be assigned by IANA (suggested value =1)
Length 8 (IPv4) or 20 (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.
4.1.2. PATH-SCOPE sub-TLV
The PATH-SCOPE sub-TLV indicates the PCE path computation scope,
which refers to the PCE's ability to compute or take part in 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 and four fields indicating PCE preferences.
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The PATH-SCOPE sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5| Reserved |PrefL|PrefR|PrefS|PrefY| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =2)
Length 4
Value This comprises a 2 byte flag field 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 paths
1 R bit: Can act as PCE for inter-area TE LSP
computation
2 Rd bit: Can act as a default PCE for inter-area TE LSP
computation
3 S bit: Can act as PCE for inter-AS TE LSP computation
4 Sd bit: Can act as a default PCE for inter-AS TE LSP
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: PCE's preference for inter-area TE LSPs computation.
Pref-S field: PCE's 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, or 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 (that is the PCE can compute a
path towards any neighbor area). Similarly, when set, the Sd bit
indicates that the PCE can act as a default PCE for inter-AS TE LSP
computation (the PCE can compute a path towards any neighbor AS).
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When the Rd bit is set the PCE-NEIG-DOMAIN TLV (see 5.1.4) MUST NOT
contain any Area ID DOMAIN sub-TLVs.
Similarly, when the Sd bit is set the PCE-NEIG-DOMAIN TLV MUST NOT
contain any AS-DOMAIN sub-TLVs.
When the R/S bit is cleared, the Rd/Sd bit SHOULD be cleared and MUST
be ignored.
The PrefL, PrefR, PrefS and PrefY fields are each three bits 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 for each computation scope to each PCE so as
to balance the path computation load among them. The algorithms used
by a PCC to load balance its path computation requests according to
such PCE preference is out of the scope of this document and is a
matter for local or network wide policy. The same or distinct
preferences may be used for each scope. 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 L bit, R bit, S bit or Y bit are cleared, the PrefL, PrefR,
PrefS, PrefY fields SHOULD respectively be set to 0 and MUST be
ignored.
Both reserved fields SHOULD be set to zero on transmission and MUST
be ignored on receipt.
4.1.3. PCE-DOMAINS sub-TLV
The PCE-DOMAINS sub-TLV specifies the set of domains (areas and/or
ASes) where the PCE has topology visibility and through which the PCE
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 MAY 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 (see section 5 for a
discussion of how the flooding scope is set and interpreted).
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The PCE-DOMAINS sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// 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 paths.
Two DOMAIN sub-TLVs are defined:
Sub-TLV type Length Name
1 variable Area ID sub-TLV
2 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 include exactly one AS number sub-TLV, and MUST NOT
contain an area ID sub-TLV.
4.1.3.1. Area ID DOMAIN sub-TLV
The Area ID DOMAIN sub-TLV carries an IPv4 OSPF area identifier. It
has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 1
Length 4
Value Four octet OSPF Area ID
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4.1.3.2. AS Number sub-TLV
The AS Number sub-TLV carries an AS number. It has the following
format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 2
Length 4
AS Number: AS number identifying an AS. When coded in 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.
4.1.4. PCE-NEIG-DOMAINS sub-TLV
The PCE-NEIG-DOMAINS sub-TLV specifies the set of neighbour domains
(areas, ASes) 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 path transits one of these domains. It contains a set of one or
more sub-TLVs where each sub-TLV identifies a domain.
The PCE-NEIG-DOMAINS sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// DOMAIN sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be defined by IANA (suggested value =4)
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
neighbour domain toward which a PCE can compute paths.
The PCE-NEIG-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.
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The PCE-NEIG-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.
4.1.5. PCE-CAP-FLAGS sub-TLV
The PCE-CAP-FLAGS sub-TLV is an optional TLV used to indicate PCE
capabilities. It MAY be present within the PCED TLV. It MUST NOT be
present more than once.
The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array
of units of 32 flags numbered from the most significant as bit zero,
where each bit represents one PCE capability.
The format of the PCE-CAP-FLAGS 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// PCE Capability Flags //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type To be assigned by IANA (suggested value =5)
Length Multiple of 4 bytes
Value This contains an array of units of 32 bit flags
numbered from the most significant as bit zero, where
each bit represents one PCE capability.
IANA is requested to manage the space of the PCE Capability Flags
The following bits are to be assigned by IANA:
Bit Capabilities
0 Capability to handle GMPLS link constraints
1 Capability to compute bidirectional paths
2 Capability to compute PSC path
3 Capability to compute a TDM path
4 Capability to compute a LSC path
5 Capability to compute a FSC path
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6 Capability to compute link/node/SRLG diverse paths
7 Capability to compute load-balanced paths
8 Capability to compute a set of paths in a
synchronized Manner
9 Support for multiple objective functions
10 Capability to handle path constraints (e.g. max hop count,
max path metric)
11 Support for Request prioritization.
12 Support for multiple requests within the same
request message.
13-31 Reserved for future assignments by IANA.
Reserved bits SHOULD be set to zero on transmission and MUST be
ignored on receipt.
4.1.6. The CONGESTION sub-TLV
The CONGESTION sub-TLV is used to indicate a PCE's processing
congestion state and may optionally include the expected PCE
congestion duration.
The CONGESTION sub-TLV is optional, it MAY be carried within the PCED
TLV. It MUST NOT be present more than once.
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 =6)
Length 4
Value
-C bit: When set this indicates that the PCE is experiencing
congestion and cannot accept any new request. When
cleared this indicates that the PCE is not
experiencing 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.
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When C is cleared the Congestion Duration SHOULD be set to 0 and MUST
be ignored.
5. Elements of Procedure
The PCED TLV is advertised within OSPFv2 Router Information LSAs
(Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router information
LSAs (function code of 12) which are defined in [OSPF-CAP]. As such,
elements of procedure are inherited from those defined in [OSPF-CAP].
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
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
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.
A PCE MUST originate a new OSPF Router Information LSA whenever the
content of the PCED TLV changes or whenever required by the regular
OSPF refresh procedure.
When the PCE function is deactivated on a node, the node MUST
originate a new Router Information LSA that does no longer contain
the PCED TLV. A PCC MUST be able to detect that the PCED TLV has been
removed from a Router Information LSA.
The PCE address, i.e. the address indicated within the PCE ADDRESS
TLV, MUST be distributed as part of OSPF routing; this allows
speeding up the detection of a PCE failure. Note that when the PCE
address is no longer reachable, this means that the PCE node has
failed or has been torn down, or that there is no longer IP
connectivity to the PCE node.
The PCED TLV is OPTIONAL. When an OSPF LSA does not contain any PCED
TLV, this means that the PCE information of that node is unknown.
A change in PCED information MUST NOT trigger any SPF computation at
a receiving router.
The way PCEs determine the information they advertise 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
automatically determined by the PCE (e.g., areas of visibility).
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5.1. CONGESTION sub-TLV specific procedures
When a PCE enters into a processing congestion state, the conditions
of which are implementation dependent, it MAY originate a Router
Information LSA with a CONGESTION sub-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
CONGESITON sub-TLV was null, it SHOULD originate a CONGESTION sub-TLV
with the C bit cleared and a null congestion duration;
- If the congestion duration in the previously originated
CONGESTION sub-TLV was non null, it MAY originate a CONGESTION sub-
TLV with the C bit cleared. Note that in some particular cases it may
be desired to originate a CONGESTION sub-TLV with the C bit cleared
if the congestion duration was over estimated.
The congestion duration allows a reduction in the amount of OSPF
flooding, as only uncongested-to-congested state transitions need to
be advertised.
A PCE 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 performance. 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 CONGESTION sub-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 PCE that is no longer congested.
6. Backward compatibility
The PCED TLV defined in this document does not introduce any
interoperability issues.
A router not supporting the PCED TLV will just silently ignore the
TLV as specified in [OSPF-CAP].
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7. IANA Considerations
7.1. OSPF TLV
Once a registry for the Router Information LSA defined in
[OSPF-CAP] will have been assigned, IANA will assign a new
OSPF TLV code-point for the PCED TLV carried within the Router
Information LSA.
Value Sub-TLV References
----- -------- ----------
5 PCED TLV (this document)
7.2. PCED sub-TLVs registry
The PCED TLV referenced above is constructed from sub-TLVs. Each sub-
TLV includes a 16-bit type identifier.
The IANA is requested to create a new registry and manage TLV type
identifiers as follows:
- TLV Type
- TLV Name
- Reference
This document defines five TLVs as follows (suggested values):
Value TLV name References
----- -------- ----------
1 PCE-ADDRESS This document
2 PATH-SCOPE This document
3 PCE-DOMAINS This document
4 PCE-NEIG-DOMAINS This document
5 PCE-CAP-FLAGS This document
6 CONGESTION This document
New TLV type values may be allocated only by an IETF Consensus
action.
7.3. PCE Capability Flags registry
This document provides new capability bit flags, which are present
in the PCE-CAP-FLAGS TLV referenced in section 4.1.5.
The IANA is requested to create a new registry and to manage the
space of PCE capability bit flags numbering them in the usual IETF
notation starting at zero and continuing at least through 31, with
the most significant bit as bit zero.
The same registry is defined for IS-IS based PCE discovery [PCED-
ISIS]. A single registry must be defined for both protocols.
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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
- Capability Description
Several bits are defined in this document. Here are the suggested
values:
Bit Capability Description
0 GMPLS link constraints
1 Bidirectional paths
2 PSC paths
3 TDM paths
4 LSC paths
5 FSC paths
6 Diverse paths
7 Load-balanced paths
8 Synchronized computation
9 Multiple objective functions
10 Additive path constraints (e.g. max hop count)
11 Request prioritization
12 Multiple requests per message
8. Security Considerations
This document defines OSPF extensions for PCE discovery within an
administrative domain. Hence the security of the PCE discovery relies
on the security of OSPF.
Mechanisms defined to ensure authenticity and integrity of OSPF LSAs
[RFC2154], and their TLVs, can be used to secure the PCE Discovery
information as well.
OSPF provides no mechanism for protecting the privacy of LSAs, and in
particular the PCE discovery information.
9. Manageability Considerations
Manageability considerations for PCE Discovery are addressed in
section 4.10 of [RFC4674].
9.1. Control of Policy and Functions
Requirements on the configuration of PCE discovery parameters on PCCs
and PCEs are discussed in section 4.10.1 of [RFC4674].
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Particularly, a PCE implementation SHOULD allow configuring the
following parameters on the PCE:
-The PCE IPv4/IPv6 address(es) (see section 4.1.1)
-The PCE Scope, including the inter-domain functions (inter-
area, inter-AS, inter-layer), the preferences, and whether the
PCE can act as default PCE (see section 4.1.2)
-The PCE domains (see section 4.1.3)
-The PCE neighbour domains (see section 4.1.4)
-The PCE capabilities (see section 4.1.5)
9.2. Information and Data Model
A MIB module for PCE Discovery is defined in [PCED-MIB].
9.3. Liveness Detection and Monitoring
PCE Discovery Protocol liveness detection relies upon OSPF liveness
detection. OSPF already includes a liveness detection mechanism
(Hello protocol), and PCE discovery does not require additional
capabilities.
Procedures defined in section 5 allow a PCC detecting when a PCE has
been deactivated, or is no longer reachable.
9.4. Verify Correct Operations
The correlation of information advertised against information
received can be achieved by comparing the PCED information in the PCC
and in the PCE, which is stored in the PCED MIB [PCED-MIB]. The
number of dropped, corrupt, and rejected information elements are
stored in the PCED MIB.
9.5. Requirements on Other Protocols and Functional Components
The OSPF extensions defined in this documents does not imply any
requirement on other protocols.
9.6. Impact on network operations
Frequent changes in PCE information, and particularly in PCE
congestion information, may have a significant impact on OSPF and
might destabilize the operation of the network by causing the PCCs to
swap between PCEs.
As discussed in section 5, a PCE implementation SHOULD support an
appropriate dampening algorithm so as to dampen OSPF flooding in
order to not impact the OSPF scalability.
Also, as discussed in section 4.10.4 of [RFC4674], it MUST be
possible to apply at least the following controls:
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- Configurable limit on the rate of announcement of changed
parameters at a PCE.
- Control of the impact on PCCs such as through discovery messages
rate-limiting.
- Configurable control of triggers that cause a PCC to swap to
another PCE.
10. Acknowledgments
We would like to thank Lucy Wong and Adrian Farrel for their useful
comments and suggestions.
11. References
11.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2740] 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.
11.2. Informative references
[RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", RFC4657, September 2006.
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[PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1", draft-ietf-pce-pcep, work
in progress.
[PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path
Computation Element Discovery", draft-ietf-pce-disc-mib-00, work in
progress.
[PCED-ISIS] Le Roux, Vasseur, et al. "IS-IS protocol extensions for
Path Computation Element (PCE) Discovery", draft-ietf-pce-disco-
proto-isis, work in progress.
12. 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
13. 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@bt.infonet.com
14. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
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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
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
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rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
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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
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Copyright Statement
Copyright (C) The IETF Trust (2007). This document is subject to the
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Le Roux, Vasseur et al. OSPF extensions for PCE Discovery [Page 22]
