Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Category: Standard Track
Expires: September 2006 J.P. Vasseur (Editor)
Cisco System Inc.
Yuichi Ikejiri
NTT Communications
Raymond Zhang
BT Infonet
March 2006
IGP protocol extensions for Path Computation Element (PCE) Discovery
draft-ietf-pce-disco-proto-igp-01.txt
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Abstract
There are various circumstances in which 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 used 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
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PCE discovery consists of relying on IGP flooding. For that purpose
this document defines OSPF and ISIS extensions for the advertisement
of PCE Discovery information within an IGP area or the entire 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........................................................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..............................11
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
5.2. The OSPF PCES TLV..........................................15
5.2.1. The CONGESTION sub-TLV.....................................16
5.3. Elements of Procedure......................................16
5.3.1. PCED TLV Procedure.........................................17
5.3.2. PCES TLV procedure.........................................17
6. ISIS extensions............................................19
6.1. IS-IS PCED TLV format......................................19
6.1.1. PCE-ADDRESS sub-TLV........................................20
6.1.2. The PATH-SCOPE sub-TLV.....................................20
6.1.3. PCE-DOMAINS sub-TLV........................................22
6.1.3.1. Area ID DOMAIN sub-TLV...................................22
6.1.3.2. AS Number DOMAIN sub-TLV.................................23
6.1.4. PCE-DEST-DOMAINS sub-TLV...................................23
6.1.5. GENERAL-CAP sub-TLV........................................23
6.1.6. The PATH-COMP-CAP sub-TLV..................................24
6.2. The ISIS PCES TLV..........................................25
6.2.1. The CONGESTION sub-TLV.....................................25
6.3. Elements of Procedure......................................26
6.3.1. PCED TLV Procedure.........................................26
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6.3.2. PCES TLV procedure.........................................27
7. Backward compatibility.....................................27
8. IANA considerations........................................28
8.1. OSPF TLVs..................................................28
8.2. ISIS TLVs..................................................28
8.3. Capability bits............................................29
9. Security Considerations....................................29
10. References.................................................29
10.1. Normative references........................................29
10.2. Informative references......................................30
11. Authors' Addresses:........................................30
12. Intellectual Property Statement............................31
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]) respectively. 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
ABR: IGP Area Border Router (OSPF ABR or ISIS L1L2 router).
AS: Autonomous System.
ASBR: AS Border Router.
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 Area: OSPF Area or ISIS level.
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).
LSR: Label Switch Router.
PCC: Path Computation Client: any client application requesting a
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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.
PCECP: Path Computation Element Communication Protocol.
TE LSP: Traffic Engineered Label Switched Path
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. The
requirements for such communication protocol can be found in [PCECP-
REQ] 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 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, 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 [PCE-DISCO-REQ].
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, ISIS), 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 and ISIS extensions allowing a PCE
participating in 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]. This document
also defines extensions allowing a PCE participating to the IGP to
advertise its potential processing congestion state.
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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. Such IGP extensions fully satisfy the
aforementioned dynamic PCE discovery requirements.
This document defines two new TLVs (named the PCE Discovery (PCED)
TLV and the PCE Status (PCES) TLV) for ISIS and OSPF to be carried
within the ISIS Capability TLV ([ISIS-CAP]) and 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 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.
The routing extensions defined in this document allow for PCE
discovery within an IGP Routing domain. Solutions for PCE discovery
across AS boundaries are beyond the scope of this document, and for
further study.
4. Overview
4.1. PCE Information
PCE information advertised within the IGP includes PCE Discovery
Information and PCE Status information.
4.1.1. PCE Discovery Information
The PCE Discovery information is comprised of:
- The PCE location: This is a set of one or more IPv4 and or IPv6
addresses that MUST be used to reach the PCE. It is RECOMMENDED to
use loopback addresses always reachable.
- 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 PCE Destination domain(s): This is the set of destination
domain(s) towards which a PCE can compute paths.
- A set of general PCECP capabilities (e.g. support for request
prioritization) and path computation specific capabilities
(e.g. supported constraints, supported objective functions
).
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These are two variable length sets of bits flags, where each bit
represent a given PCE capability.
It may also contain optional elements to describe more complex
capabilities.
PCE Discovery information is by nature a static information that does
not change with PCE activity. Changes in PCE Discovery information
may occur as a result of PCE configuration updates, PCE
deployment/activation or PCE deactivation/suppression. Hence, this
information is not expected to change frequently.
4.1.2. PCE Status Information
The PCE Status is optional information that can be used to report a
PCE processing congested state along with an estimated congestion
duration. This dynamic information 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 IGP areas the PCE belongs to or can be extended across
the entire 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
[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
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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):
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 PCE-DEST-DOMAINS are optional. They MUST
be present only in some specific inter-domain cases.
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], the opaque type of which is determined by the
desired flooding scope.
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5.1.1. PCE-ADDRESS sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address that MUST be used to
reach the PCE. It is RECOMMENDED to make use of 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 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.
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 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 =3)
Length Variable
Value This comprises a 2 bytes flag where each bit
represents a supported path scope, as well as four
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
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 L bit, R bit, S or Y bit are cleared the PrefL, PrefR,
PrefS, PrefY bit 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 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 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 //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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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
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
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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 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.
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.
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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 PCECP
related capabilities.
The value field of the GENERAL-CAP sub-TLV is made of bit flags,
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 PCE Capabilities |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
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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 TLV used to indicate path
computation specific capabilities. It is made of a set of bit flags,
where each bit correspond 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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:
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Bit Capabilities
0 G bit: Capability to handle GMPLS contraints
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
6-31 Reserved for future assignments by IANA.
The G, B, D, L, S and O bits are not exclusive.
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
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
The PCE-ADDRESS and CONGESTION sub-TLVs MUST be present once
in 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 the processing congestion state information is applied to. This
is required as the PCES and PCED TLVs may be carried in separate
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Router Information LSAs.
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. It MUST be carried once 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
congestion and cannot support any new request. When
cleared this indicates that the PCE does not
experiences congestion an can support a new request.
-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.
5.3. Elements of Procedure
The PCED and PCES TLV are carried within an OSPF Router information
opaque LSA (opaque type of 4, opaque ID of 0) which is 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.
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5.3.1. PCED TLV Procedure
A router MUST originate a new OSPF router information LSA whenever
the content of the PCED TLV 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.
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 sub-TLVs are OPTIONAL. When an OSPF LSA does not contain
any PCED sub-TLV, this means that the PCE information of that
node is unknown.
Note that a change in PCED 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
automatically retrieved by the PCE (e.g. areas of visibility).
5.3.2. PCES TLV procedure
A router MUST originate a new OSPF router information LSA whenever
the content of the PCES TLV changes or whenever required by the
regular OSPF procedure (LSA refresh (every LSRefreshTime)).
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 leaves the processing congestion state, the conditions of
which are implementation dependent, there are two cases:
- 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 not 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 saturation duration was over estimated.
The congestion duration allows reducing the amount of OSPF flooding,
as only uncongested-congested state transitions are flooded.
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It is expected that a proper implementation will support dampening
algorithms so as to dampen OSPF flooding in order to not impact the
OSPF scalability. It is recommended to introduce some hysteresis for
saturation state transition, so as to avoid state oscillations that
may impact OSPF performances. For instance two thresholds could be
configured: A resource saturation upper-threshold and a resource
saturation 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. Such PCC procedures are out of the scope of
this document.
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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 3 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 PCE-DEST-DOMAINS are optional. They MUST
be present only in some specific inter-domain cases.
The GENERAL-CAP and PATH-COMP-CAP 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 PCE information.
The PCED TLV is carried within an ISIS CAPABILITY TLV defined in
[ISIS-CAP], whose S bit is determined by the desired flooding scope.
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6.1.1. PCE-ADDRESS sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address that MUST be used to
reach the PCE. It is RECOMMENDED to make use of a loop-back addresse
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 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 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.
The PATH-SCOPE sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =2)
LENGTH: 3
VALUE: This comprises a one-byte flag of bits where each bit
represents a supported path scope, followed by a 2-bytes
preferences field indicating PCE preferences.
Here is the structure of the bit flag:
+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5|Res|
+-+-+-+-+-+-+-+-+
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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
6-7 Reserved for future usage.
Here is the structure of the preferences field
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PrefL|PrefR|PrefS|PrefY| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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).
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
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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 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 L bit, R bit, S or Y bit are cleared the PrefL, PrefR,
PrefS, PrefY bit MUST respectively be set to 0.
6.1.3. PCE-DOMAINS sub-TLV
The PCE-DOMAINS sub-TLV specifies the set of domains (areas or 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 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
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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:
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 destinations are located within 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 =3)
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.
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.
6.1.5. GENERAL-CAP sub-TLV
The GENERAL-CAP sub-TLV is an optional TLV used to indicate PCECP
related capabilities.
This is a series of bits flags, where each bit corresponds to a
general PCE capability. It MAY also include optional sub-TLVs to
encode more complex capabilities.
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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.
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 an optional TLV used to indicate path
computation specific capabilities of a PCE.
This is a series of bit flags, where each bit correspond to a path
computation capability. It MAY also include optional sub-TLVs to
encode more complex capabilities.
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|
+-+-+-+-+-+-+-+-+
G bit: Capability to handle GMPLS constraints
B bit: Capability to compute bidirectional paths
D bit: Capability to compute link/node/SRLG diverse paths
L bit: Capability to compute load-balanced paths
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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.
The G, B, D, L, S and O bits are not exclusive.
6.2. The ISIS PCES TLV
The ISIS PCE Status TLV (PCES TLV) carries information related to PCE
processing congestion state.
The PCES TLV is carried within an ISIS Capability TLV which is
defined in [ISIS-CAP].
The ISIS PCES 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 two sub-TLVs are defined (suggested type values to be
assigned by IANA):
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 3 CONGESTION sub-TLV
The PCE-ADDRESS and CONGESTION sub-TLVs MUST be present once
in a PCES TLV. The PCE-ADDRESS sub-TLV is defined in section 6.1.1.
It carries one of the PCE IP addresses and is used to identify the
PCE the processing congestion state information is applied to. This
is required as the PCES and PCED TLVs may be carried in separate
ISIS Capability TLVs.
Any non recognized sub-TLV MUST be silently ignored.
Additional sub-TLVs could be added in the future to advertise
additional congestion information.
6.2.1. 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 PCE
expected congestion duration.
The CONGESTION sub-TLV is mandatory. It MUST be carried once within
the PCES TLV.
The format of the CONGESTION sub-TLV is as follows:
TYPE: To be assigned by IANA (Suggested value =2)
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LENGTH: 3
VALUE: This comprises a one-byte flag of bits indicating the
congestion status, followed by a 2-bytes field indicating the
congestion duration.
Here is the TLV structure
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Reserved| Congestion Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value
-C bit: When set this indicates that the PCE experiences
congestion and cannot support any new request. When
cleared this indicates that the PCE does not
experiences congestion an can support a new request.
-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.
6.3. Elements of Procedure
The PCED and PCES TLV are carried within an ISIS Capability TLV which
is defined in [ISIS-CAP]. As PCES information is likely to change
more frequently than the PCED information, it is RECOMMENDED to carry
PCES and PCED TLVs in separate ISIS Capability TLVs, so as not to
carry all PCED information each time the PCE status changes.
6.3.1. PCED TLV Procedure
An ISIS router MUST originate a new ISIS LSP whenever the content
of any of the PCED TLV changes or whenever required by the regular
ISIS 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 only the L bit of the PATH-SCOPE sub-TLV is set and
the flooding scope MUST be local.
PCED sub-TLVs are OPTIONAL. When an ISIS LSP does not contain
any PCED sub-TLV, this means that the PCE information of
that node is unknown.
Note that a change in PCED information MUST not trigger any SPF
computation.
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The way PCEs retrieve their own information is out of the scope of
this document. Some information may be configured (e.g. address,
preferences, scope) and other information may be automatically
retrieved (e.g. areas of visibility).
6.3.2. PCES TLV procedure
An ISIS router MUST originate a new ISIS LSP whenever the content
of any of the PCES TLV changes or whenever required by the regular
IS-IS procedure (LSP refresh).
When a PCE enters into a processing congestion state, the conditions
of which are implementation dependent, it SHOULD originate a new ISIS
LSP with a Capability TLV carrying a PCES TLV with the C bit set and
optionally a non-null expected congestion duration.
When a PCE leaves the processing congestion state, the conditions of
which are implementation dependent, there are two cases:
- 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 not 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 saturation duration was over estimated.
The congestion duration allows reducing the amount of ISIS flooding,
as only uncongested-congested state transitions are flooded.
It is expected that a proper implementation will support dampening
algorithms so as to dampen ISIS flooding in order to not impact the
ISIS scalability. It is recommended to introduce some hysteresis for
congestion state transition, so as to avoid state oscillations that
may impact ISIS performances. For instance two thresholds could be
configured: A resource saturation upper-threshold and a resource
saturation 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. Such PCC procedures are out of the scope of
this document.
7. Backward compatibility
The PCED and PCEs TLVs defined in this document do not introduce any
interoperability issue.
For OSPF, a router not supporting the PCED/PCES TLVs SHOULD just
silently ignore the TLVs as specified in [RFC2370].
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For ISIS a router not supporting the PCED/PCES TLVs SHOULD just
silently ignore the TLV.
8. IANA considerations
8.1. 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)
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)
IANA will assign a new codepoint for the OSPF PCES TLV defined in
this document and carried within the Router Information LSA.
Two sub-TLVs types are defined for this TLV and should be assigned by
IANA:
-PCE-ADDRESS sub-TLV (suggested value = 1)
-CONGESTION sub-TLV (suggested value = 2)
8.2. 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-DEST-DOMAINS sub-TLV (suggested value = 3)
-PCE-DOMAINS sub-TLV (suggested value = 4)
-GENERAL-CAP sub-TLV (suggested value = 5)
-PATH-COMP-CAP sub-TLV (suggested value = 6)
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)
IANA will assign a new codepoint for the ISIS PCES TLV defined in
this document and carried within the ISIS CAPABILITY TLV.
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Two sub-TLVs types are defined for this TLV and should be assigned by
IANA:
-PCE-ADDRESS sub-TLV (suggested value = 1)
-CONGESTION sub-TLV (suggested value = 2)
8.3. 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 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 functions
9. Security Considerations
To be completed in further revisions.
10. References
10.1. 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.
Le Roux, et al. IGP extensions for PCE discovery [Page 29]
Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006
[RFC2370] Coltun, R., The OSPF Opaque LSA Option, RFC 2370, July
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
10.2. Informative references
[PCECP-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs, work in
progress.
[PCEP] Vasseur et al., Path Computation Element (PCE) communication
Protocol (PCEP) - Version 1, draft-ietf-pce-pcep-01.txt, work in
progress.
11. Authors' Addresses:
Jean-Louis Le Roux (Editor)
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@francetelecom.com
Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc.
1414 Massachusetts avenue
Boxborough , MA - 01719
Le Roux, et al. IGP extensions for PCE discovery [Page 30]
Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006
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
Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA
Email: raymond_zhang@infonet.com
12. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
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
Le Roux, et al. IGP extensions for PCE discovery [Page 31]
Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Le Roux, et al. IGP extensions for PCE discovery [Page 32]
