One document matched: draft-ietf-pce-disco-proto-isis-00.txt
Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Category: Standard Track
Expires: March 2007 J.P. Vasseur (Editor)
Cisco System Inc.
Yuichi Ikejiri
NTT Communications
Raymond Zhang
BT Infonet
September 2006
IS-IS protocol extensions for Path Computation Element (PCE) Discovery
draft-ietf-pce-disco-proto-isis-00.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 be 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 ISIS extensions for the advertisement of PCE
Discovery information within an ISIS area or within the entire ISIS
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. ISIS extensions.............................................6
5.1. IS-IS PCED TLV format.......................................6
5.1.1. PCE-ADDRESS sub-TLV.........................................7
5.1.2. The PATH-SCOPE sub-TLV......................................7
5.1.3. PCE-DOMAINS sub-TLV.........................................9
5.1.3.1. Area ID DOMAIN sub-TLV...................................10
5.1.3.2. AS Number DOMAIN sub-TLV.................................10
5.1.4. PCE-DEST-DOMAINS sub-TLV...................................10
5.1.5. GENERAL-CAP sub-TLV........................................11
5.1.6. The PATH-COMP-CAP sub-TLV..................................12
5.1.6.1. Objective Functions sub-TLV..............................13
5.1.6.2. Opaque Objective Function sub-TLV........................13
5.1.6.3. Switch Caps sub-TLV......................................14
5.2. The ISIS PCES TLV..........................................14
5.2.1. The CONGESTION sub-TLV.....................................15
6. Elements of Procedure......................................16
6.1.1. PCES TLV specific procedure................................16
7. Backward compatibility.....................................17
8. IANA considerations........................................17
8.1. ISIS TLVs..................................................17
8.2. Capability bits............................................18
9. Security Considerations....................................19
10. References.................................................19
10.1. Normative references.......................................19
10.2. Informative references.....................................19
11. Authors' Addresses:........................................20
12. Intellectual Property Statement............................20
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1. Note
This document specifies sub-TLVs to be carried within the ISIS Router
Capability TLV ([ISIS-CAP]). Because this document does not introduce
any new ISIS element of procedure it will be discussed within the PCE
Working Group with a review of the ISIS Working Group.
2. Terminology
Terminology used in this document
ABR: IGP Area Border Router (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.
Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries.
Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries.
Inter-area TE LSP: A TE LSP whose path transits through
two or more IGP areas.
Inter-AS 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
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.
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3. Introduction
[RFC4655] 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-DISC-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 thisan IGP routing domain consists
of relying on IGP advertisements.
This document defines ISIS extensions allowing a PCE participating to
the ISIS routing 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 ISIS
routing to advertise its potential processing congestion state.
Generic capability mechanisms for ISIS have been defined in [ISIS-
CAP] the purpose of which is to allow a router to advertise its
capability within an ISIS area or an entire ISIS routing domain. Such
ISIS extensions fully satisfy the aforementioned dynamic PCE
discovery requirements.
This document defines two new sub-TLVs (named the PCE Discovery
(PCED) TLV and the PCE Status (PCES) TLV) for ISIS, to be carried
within the ISIS Capability TLV ([ISIS-CAP]). The PCE information
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advertised is detailed in section 4. Protocol extensions and
procedures are defined in section 5 and 6.
This document does not define any new ISIS element of procedure but
how the procedures defined in [ISIS-CAP] should be used.
The routing extensions defined in this document allow for PCE
discovery within an ISIS Routing domain. Solutions for PCE discovery
across AS boundaries are beyond the scope of this document, and for
further study.
Similar extensions to OSPF for PCE discovery can be found in [OSPF-
PCE-DISCO].
4. Overview
4.1. PCE Information
PCE information advertised within ISIS 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 an IPv4 and/or IPv6 address that must be
used to reach the PCE. It is RECOMMENDED to use addresses always
reachable;
- The PCE inter-domain functions: this refers to the PCE path
computation scope (i.e. inter-area, inter-AS, inter-layer…);
- The PCE domain(s): This is the set of one or more domain(s) where
the PCE has visibility and can compute paths;
- The PCE Destination domain(s): This is the set of one or more
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).
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, PCE deactivation/suppression or PCE failure.
Hence, this information is not expected to change frequently.
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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 is a dynamic information, which may change with PCE
activity.
Procedures for a PCE to move from a processing congested state to a
non congested state are beyond the scope of this document, but the
rate at which a PCE Status change is advertised MUST not impact by
any mean the IGP scalability. Particular attention should be given on
procedures to avoid state oscillations.
4.2. Flooding scope
The flooding scope for PCE Discovery Information can be limited to
one or more ISIS areas the PCE belongs to or can be extended across
the entire ISIS 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. ISIS extensions
5.1. 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
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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 MAY
be present in some specific inter-domain cases.
The sub-TLVs 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.
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 an address
that is always reachable, provided the PCE is alive.
The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
PCED TLV. It MAY appear twice, when the PCE has both an IPv4 and
IPv6 address. It MUST not appear more than twice.
The PCE-ADDRESS sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =1)
LENGTH: 5 for IPv4 address and 17 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
5.1.2. 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).
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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 bits flag:
+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5|Res|
+-+-+-+-+-+-+-+-+
Bit Path Scope
0 L bit: Can compute intra-area path
1 R bit: Can act as PCE for inter-area TE LSPs
computation
2 Rd bit: Can act as a default PCE for inter-area TE LSPs
computation
3 S bit: Can act as PCE for inter-AS TE LSPs computation
4 Sd bit: Can act as a default PCE for inter-AS TE LSPs
computation
5 Y bit: Can compute or take part into the computation of
paths across layers
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: 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.
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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 mutually 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
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 PCE’s preference are 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 fields MUST respectively be set to 0.
5.1.3. PCE-DOMAINS sub-TLV
The PCE-DOMAINS sub-TLV specifies the set of domains (areas 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.
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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.
5.1.3.1. Area ID DOMAIN sub-TLV
This sub-TLV carries an ISIS area ID. It has the following format
TYPE: To be assigned by IANA (Suggested value =1)
LENGTH: Variable
VALUE: This comprises a variable length ISIS area ID. This is the
combination of an Initial Domain Part (IDP) and High Order
part of the Domain Specific part (HO-DSP)
5.1.3.2. 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.
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 DOMAIN sub-TLVs where each DOMAIN sub-
TLV identifies a domain.
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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.
5.1.5. GENERAL-CAP sub-TLV
The GENERAL-CAP sub-TLV is an optional TLV used to indicate PCECP
related capabilities. It carries a 32-bit flag, where each bit
corresponds to a general PCE capability. It MAY also include optional
sub-TLVs to encode more complex capabilities.
The GENERAL-CAP sub-TLV has the following format:
TYPE: To be assigned by IANA (Suggested value =4)
LENGTH: Variable
VALUE: This comprises a 32-bit General Capabilities flag where
each bit corresponds to a general PCE capability, and
optional sub-TLVs that may be defined to specify more
complex capabilities. Currently no sub-TLVs are defined.
The following bits in the General Capabilities 32-bit flag are to be
assigned by IANA:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|M| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Bit Capabilities
0 P bit: Support for Request prioritization.
1 M bit: Support for multiple requests 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 of a PCE.
It comprises a 32-bit flag, where each bit corresponds to a path
computation capability. It MAY also include optional sub-TLVs to
encode more complex capabilities.
The PATH-COMP-CAP sub-TLV has the following format:
TYPE: To be assigned by IANA (suggested value = 5)
LENGTH: Variable
VALUE: This comprises one 32 bit Path Computation Capabilities
Flag, where each bit corresponds to a path computation
capability, and optional sub-TLVs that may be defined to
specify more complex capabilities. Three optional sub-TLVs
are currently defined.
The following bits in the Path Computation Capabilities 32-bit Flag
are to be assigned by IANA:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|B|D|L|S|0|P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Bit Capabilities
0 G bit: Capability to handle GMPLS link 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 P bit: Capability to handle path constraints (e.g. max hop
count, metric bound)
7-31 Reserved for future assignments by IANA.
The G, B, D, L, S, O and P bits are not exclusive.
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Three optional sub-TLVs are currently defined for the PATH-COMP-CAP
TLV:
- The Objective Functions sub-TLV (type to be defined, suggested
value =1) that carries a list of supported objective functions,
where each objective function is identified by a 16 bit integer.
- The Opaque Objective Function sub-TLV (type to be defined,
suggested value =2) that allows the user to encode a specific
objective function in any appropriate language.
- The Switch Caps sub-TLV (type to be defined, suggested value =3)
that carries a list of supported switching capabilities. This
means that the PCE can compute paths for the listed switching
capabilities.
5.1.6.1. Objective Functions sub-TLV
The format of the Objective Functions sub-TLV is as follows:
TYPE: To be defined by IANA (suggested value =1)
LENGTH: Variable (N*2)
VALUE: This comprises a set of one or more 16 bit function
ids, where each function id identifies a supported
objective functions.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| function 1 | function 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| function N | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Objectives functions and their identification will be defined in a
separate document.
The Objective Functions sub-TLV is optional. It MAY be present within
the PATH-COMP-CAP TLV. When present it MUST be present only once in
the PATH-COMP-CAP TLV.
5.1.6.2. Opaque Objective Function sub-TLV
The format of the Opaque Objective Function sub-TLV is as follows:
TYPE: To be defined by IANA (suggested value =2)
LENGTH: Variable
VALUE: This encodes a specific objective function in any
appropriate language.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque objective function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The Opaque Objective function sub-TLV is optional. The PATH-COMP-CAP TLV
MAY comprise 0, one or more Opaque Objective Functions.
5.1.6.3. Switch Caps sub-TLV
The format of the Switch Caps sub-TLV is as follows:
TYPE To be defined by IANA (suggested value =3)
LENGTH Variable = N, where N is the number of supported
switching capabilities
VALUE This comprises a set of one or more 8-bit switching
types, where each switching types identifies a
supported switching capability.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC type | SC type | SC type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Switching type values are defined in [RFC4205].
The Switch Caps sub-TLV is optional. It MAY be present in the PATH-COMP-
CAP TLV. When present it MUST be present only once in the PATH-COMP-CAP
TLV.
5.2. The 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
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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.
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 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)
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
experience 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.
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6. 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.
An ISIS router MUST originate a new ISIS LSP whenever the content
of any of the PCED TLV or PCES TLV changes or whenever required by
the regular ISIS procedure (LSP refresh).
When the scope of the PCED or PCES TLV is area local it MUST be
carried within an ISIS CAPABILITY TLV having the S bit cleared.
When the scope of the PCED or PCES TLV is the entire IGP 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,
the flooding scope MUST be local.
Note that the flooding scopes of the PCED and PCES TLVs may be
distinct, in which case they are carried in distinct ISIS Capability
TLVs.
PCED and PCES sub-TLVs are OPTIONAL. When an ISIS LSP does not
contain any PCED or PCES sub-TLV, this means that the PCE information
of that node is unknown.
Note that a change in PCED or PCES information MUST not trigger any
SPF computation.
The way PCEs retrieve their own information is out of the scope of
this document. Some information may be configured (e.g. address,
preferences, scope) and other information may be automatically
retrieved (e.g. areas of visibility).
6.1.1. PCES TLV specific procedure
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;
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- If the congestion duration in the previously originated PCES
TLV was non null, it MAY originate a PCES TLV. Note that in some
particular cases it may be desired to originate a PCES TLV with the C
bit cleared if the saturation duration was over estimated.
The congestion duration allows reducing the amount of ISIS flooding,
as only uncongested-congested state transitions are flooded.
An implementation SHOULD support an appropriate dampening algorithm
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 MAY 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.
7. Backward compatibility
The PCED and PCES TLVs defined in this document do not introduce any
interoperability issue.
An ISIS router not supporting the PCED/PCES TLVs SHOULD just silently
ignore the TLV as specified in [ISIS-CAP].
8. IANA considerations
8.1. ISIS TLVs
IANA will assign a new codepoint for the PCED TLV defined in this
document and carried within the ISIS CAPABILITY TLV.
IANA is requested to manage sub-TLV types for the PCED TLV.
Five sub-TLVs types are defined for the PCED TLV and should be
assigned by IANA:
-PCE-ADDRESS sub-TLV (suggested value = 1)
-PATH-SCOPE sub-TLV (suggested value = 2)
-PCE-DOMAINS sub-TLV (suggested value = 3)
-PCE-DEST-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:
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-Area ID sub-TLV (suggested value = 1)
-AS number sub-TLV (suggested value = 2)
Three sub-TLV types are defined for the PATH-COMP-CAP TLV and should
be assigned by IANA:
-Objective Functions sub-TLV (suggested value =1)
-Opaque Objective Function sub-TLV (suggested value =2)
-Switch Caps sub-TLV (suggested value =3)
IANA will assign a new codepoint for the ISIS PCES TLV defined in
this document and carried within the ISIS CAPABILITY TLV.
IANA is requested to manage sub-TLV types for the PCES TLV. 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. Capability bits
IANA is requested to manage the space of the General Capabilities
32-bit flag and the Path Computation Capabilities 32-bit flag defined
in this document, numbering them in the usual IETF notation starting
at zero and continuing through 31.
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
- Bit number
- Defining RFC
- Name of bit
Currently two bits are defined in the General Capabilities flag. Here
are the suggested values:
-0: Support for Request prioritization.
-1: Support for multiple messages within the same request message
Currently six bits are defined in the Path Computation Capabilities
flag. Here are the suggested values:
-0: Capability to handle GMPLS Constraints
-1: Capability to compute bidirectional paths
-2: Capability to compute link/node/SRLG diverse paths
-3: Capability to compute load-balanced paths
-4: Capability to compute a set of paths in a
synchronized Manner
-5: Support for multiple objective function
-6: Capability to handle path constraints (e.g. hop count, metric
bound)
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9. Security Considerations
This document raises no new security issues for IS-IS.
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.
[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.
[IS-IS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
Engineering", RFC 3784, June 2004.
[IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising
router information", draft-ietf-isis-caps, work in progress.
[RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE)-based Architecture", RFC4655, august 2006.
[PCE-DISCO-REQ] Le Roux, J.L., et al. "Requirements for PCE
discovery", draft-ietf-pce-discovery-reqs, work in progress
[RFC4205] Kompella, Rekhter, " IS-IS Extensions in Support of
Generalized Multi-Protocol Label Switching (GMPLS)", RFC4205, October
2005.
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, work in progress.
[OSPF-PCE-DISCO] Le Roux, Vasseur, et al., "OSPF Extensions for PCE
Discovery", draft-ietf-pce-disco-proto-ospf, work in progress.
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11. Authors' Addresses:
Jean-Louis Le Roux (Editor)
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@orange-ft.com
Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc.
1414 Massachusetts avenue
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
JAPAN
Email: y.ikejiri@ntt.com
Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA
Email: raymond_zhang@infonet.com
12. Intellectual Property Statement
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on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
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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
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Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006
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
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Copyright Statement
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.
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