Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom
Intended Status: Standard Track
Expires: March 2008 J.P. Vasseur (Editor)
Cisco System Inc.
Yuichi Ikejiri
NTT Communications
Raymond Zhang
BT Infonet
September 2007
IS-IS protocol extensions for Path Computation Element (PCE) Discovery
draft-ietf-pce-disco-proto-isis-07.txt
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Abstract
There are various circumstances where it is highly desirable for a
Path Computation Client (PCC) to be able to dynamically and
automatically discover a set of Path Computation Elements (PCE),
along with some information that can be used for PCE selection. When
the PCE is a Label Switching Router (LSR) participating in the
Interior Gateway Protocol (IGP), or even a server participating
passively in the IGP, a simple and efficient way to discover PCEs
consists of using IGP flooding. For that purpose this document
defines extensions to the Intermediate System to Intermediate System
(IS-IS) routing protocol for the advertisement of PCE Discovery
information within an IS-IS area or within the entire IS-IS 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 [RFC2119].
Table of Contents
Terminology........................................................3
1. 3
2. Introduction................................................4
3. Overview....................................................5
3.1. PCE Information.............................................5
3.1.1. PCE Discovery Information...................................5
3.1.2. PCE Overload Information....................................6
3.2. Flooding Scope..............................................6
4. The IS-IS PCED Sub-TLV......................................6
4.1. PCE-ADDRESS Sub-TLV.........................................7
4.2. The PATH-SCOPE Sub-TLV......................................7
4.3. PCE-DOMAIN Sub-TLV..........................................9
4.4. NEIG-PCE-DOMAIN Sub-TLV....................................10
4.5. PCE-CAP-FLAGS Sub-TLV......................................11
4.6. The OVERLOAD Sub-TLV.......................................11
5. Elements of Procedure......................................12
5.1. OVERLOAD Sub-TLV Specific Procedures.......................12
6. Backward Compatibility.....................................13
7. IANA Considerations........................................13
8. Security Considerations....................................13
9. Manageability Considerations...............................14
9.1. Control of Policy and Functions............................14
9.2. Information and Data Model.................................14
9.3. Liveness Detection and Monitoring..........................14
9.4. Verify Correct Operations..................................14
9.5. Requirements on Other Protocols and Functional
Components...............................................14
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9.6. Impact on Network Operations...............................15
10. Acknowledgments............................................15
11. References.................................................15
11.1. Normative References.......................................15
11.2. Informative References.....................................16
12. Editors' Addresses:........................................16
13. Contributors' Adresses:....................................16
14. Intellectual Property Statement............................17
1. Terminology
AS: Autonomous System.
IGP: Interior Gateway Protocol. Either of the two routing
protocols Open Shortest Path First (OSPF) or Intermediate System
to Intermediate system (IS-IS).
Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries.
Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries.
Inter-area TE LSP: A TE LSP whose path transits two or
more IGP areas. That is a TE-LSP that crosses at least one IGP
area boundary.
Inter-AS TE LSP: A TE LSP whose path transits two or more
ASes or sub-ASes (BGP confederations). That is a TE-LSP that
crosses at least one AS boundary.
IS-IS LSP: Link State PDU
LSR: Label Switching Router.
PCC: Path Computation Client: Any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph, and applying computational
constraints.
PCE-Domain: In a PCE context this refers to any collection of
network elements within a common sphere of address management or
path computational responsibility (referred to as "domain" in
[RFC4655]). Examples of PCE-Domains include IGP areas and ASes.
This should be distinguished from an IS-IS routing domain as
defined by [ISO].
PCEP: Path Computation Element communication Protocol.
TE LSP: Traffic Engineered Label Switched Path.
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2. Introduction
[RFC4655] describes the motivations and architecture for a Path
Computation Element (PCE)-based path computation model for Multi
Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic
Engineered Label Switched Paths (TE-LSPs). The model allows for the
separation of the PCE from a Path Computation Client (PCC) (also
referred to as a non co-located PCE) and allows for cooperation
between PCEs. This relies on a communication protocol between PCC and
PCE, and between PCEs. The requirements for such a communication
protocol can be found in [RFC4657] and the communication protocol is
defined in [PCEP].
The PCE architecture requires that a PCC be aware of the location of
one or more PCEs in its domain, and also potentially of some PCEs in
other domains, e.g. in case of inter-domain TE LSP computation.
A network may contain a large number of PCEs with potentially
distinct capabilities. In such a context it is highly desirable to
have a mechanism for automatic and dynamic PCE discovery, which
allows PCCs to automatically discover a set of PCEs, along with
additional information about each PCE that may be required for the
PCC to perform PCE selection. Additionally, it is valuable for a PCC
to dynamically detect new PCEs or any modification of the PCE
information. Detailed requirements for such a PCE discovery mechanism
are provided in [RFC4674].
Moreover, it may also be useful to discover when a PCE experiences
processing overload and when it exits such a state, in order for the
PCCs to take some appropriate actions (e.g. redirect their requests
to another PCE). Note that the PCE selection algorithm applied by a
PCC is out of the scope of this document.
When PCCs are LSRs participating in the IGP (OSPF, IS-IS), and PCEs
are either LSRs or servers also participating in the IGP, an
effective mechanism for PCE discovery within an IGP routing domain
consists of utilizing IGP advertisements.
This document defines IS-IS extensions to allow a PCE in an IS-IS
routing domain to advertise its location along with some information
useful to a PCC for PCE selection, so as to satisfy dynamic PCE
discovery requirements set forth in [RFC4674]. This document also
defines extensions allowing a PCE in an IS-IS routing domain to
advertise its processing overload state.
Generic capability advertisement mechanisms for IS-IS are defined in
[IS-IS-CAP]. These allow a router to advertise its capabilities
within an IS-IS area or an entire IS-IS routing domain. This document
leverages this generic capability advertisement mechanism to fully
satisfy the aforementioned dynamic PCE discovery requirements.
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This document defines a new sub-TLV (named PCE Discovery (PCED)) to
be carried within the IS-IS Router Capability TLV ([IS-IS-CAP]).
The PCE information advertised is detailed in section 3. Protocol
extensions and procedures are defined in section 4 and 5.
The IS-IS extensions defined in this document allow for PCE discovery
within an IS-IS Routing domain. Solutions for PCE discovery across AS
boundaries are beyond the scope of this document, and for further
study.
This document defines a set of sub-TLVs that are nested within each
other. When the degree of nesting TLVs is 2 (a TLV is carried within
another TLV) the TLV carried within a TLV is called a sub-TLV.
Strictly speaking, when the degree of nesting is 3, a subsub-TLV is
carried within a sub-TLV that is itself carried within a TLV. For the
sake of terminology simplicity, we refer to sub-TLV, a TLV carried
within a TLV regardless of the degree of nesting.
3. Overview
3.1. PCE Information
The PCE information advertised via IS-IS falls into two categories:
PCE Discovery information and PCE Overload information.
3.1.1. PCE Discovery Information
The PCE Discovery information is comprised of:
- The PCE location: an IPv4 and/or IPv6 address that is used to reach
the PCE. It is RECOMMENDED to use an address that is always
reachable;
- The PCE path computation scope (i.e. inter-area, inter-AS, inter-
layer);
- The set of one or more PCE-Domain(s) into which the PCE has
visibility and can compute paths;
- The set of one or more neighbor PCE-Domain(s) towards which a PCE
can compute paths;
- A set of communication capabilities (e.g. support for request
prioritization) and path computation specific capabilities
(e.g. supported constraints).
PCE Discovery information is by nature fairly static and does not
change with PCE activity. Changes in PCE Discovery information may
occur as a result of PCE configuration updates, PCE
deployment/activation, PCE deactivation/suppression, or PCE failure.
Hence, this information is not expected to change frequently
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3.1.2. PCE Overload Information
The PCE Overload Information is optional and can be used to report
a PCE's overload state in order to discourage the PCCs to send new
path computation requests.
A PCE may decide to clear the overload state according to local
implementation triggers (e.g. CPU utilization, average queue length
below some pre-defined thresholds). The rate at which a PCE status
change is advertised MUST NOT impact by any means the IGP
scalability. Particular attention should be given on procedures to
avoid state oscillations.
3.2. Flooding Scope
The flooding scope for PCE information advertised through IS-IS can
be a single L1 area, a L1 area and the L2 sub-domain, or the entire
IS-IS routing domain.
4. The IS-IS PCED Sub-TLV
The IS-IS PCED sub-TLV is made of a set of non ordered sub-TLVs.
The format of the IS-IS PCED sub-TLV and its sub-TLVs is identical to
the TLV format used by the Traffic Engineering Extensions to IS-IS
[RFC3784]. That is, the TLV is comprised of 1 octet for the type, 1
octet specifying the TLV length, and a value field. The Length field
defines the length of the value portion in octets.
The IS-IS PCED sub-TLV has the following format:
TYPE: To be assigned by IANA (suggested value = 5)
LENGTH: Variable
VALUE: set of sub-TLVs
Six sub-TLVs are defined:
Sub-TLV type Length Name
1 variable PCE-ADDRESS sub-TLV
2 3 PATH-SCOPE sub-TLV
3 variable PCE-DOMAIN sub-TLV
4 variable NEIG-PCE-DOMAIN sub-TLV
5 variable PCE-CAP-FLAGS sub-TLV
6 1 OVERLOAD sub-TLV
The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within
the PCED sub-TLV.
The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional. They
MAY be present in the PCED sub-TLV to facilitate selection of inter-
domain PCEs.
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The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED
sub-TLV to facilitate the PCE selection process.
The OVERLOAD sub-TLV is optional and MAY be present in the PCED sub-
TLV, to indicate a PCE's processing overload state.
Any non recognized sub-TLV MUST be silently ignored.
The PCED sub-TLV is carried within an IS-IS CAPABILITY TLV defined in
[IS-IS-CAP].
No additional sub-TLVs will be added to the PCED TLV in the future.
If a future application requires advertising additional PCE
information in IS-IS, this will not be carried in the CAPABILITY TLV.
The following sub-sections describe the sub-TLVs which may be carried
within the PCED sub-TLV.
4.1. PCE-ADDRESS Sub-TLV
The PCE-ADDRESS sub-TLV specifies the IP address that can 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 sub-TLV. It MAY appear twice, when the PCE has both an IPv4 and
IPv6 address. It MUST NOT appear more than once for the same address
type. If it appears more than once only the first occurrence MUST be
processed and other MUST be ignored.
The PCE-ADDRESS sub-TLV has the following format:
TYPE: 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
4.2. The PATH-SCOPE Sub-TLV
The PATH-SCOPE sub-TLV indicates the PCE path computation scope,
which refers to the PCE's ability to compute or take part in the
computation of intra-area, inter-area, inter-AS, or inter-layer_TE
LSP(s).
The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the
PCED sub-TLV. There MUST be exactly one instance of the PATH-SCOPE
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sub-TLV within each PCED sub-TLV. If it appears more than once only
the first occurrence MUST be processed and other MUST be ignored.
The PATH-SCOPE sub-TLV contains a set of bit flags indicating the
supported path scopes, and four fields indicating PCE preferences.
The PATH-SCOPE sub-TLV has the following format:
TYPE: 2
LENGTH: 3
VALUE: This comprises a one-octet flags field where flag
represents a supported path scope, followed by a 2-octets
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 LSP computation
2 Rd bit: Can act as a default PCE for inter-area TE LSP
computation
3 S bit: Can act as PCE for inter-AS TE LSP computation
4 Sd bit: Can act as a default PCE for inter-AS TE 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Res: Reserved for future usage.
Pref-L field: PCE's preference for intra-area TE LSPs computation.
Pref-R field: PCE's preference for inter-area TE LSPs computation.
Pref-S field: PCE's preference for inter-AS TE LSPs computation.
Pref-Y field: PCE's preference for inter-layer TE LSPs computation.
Res: Reserved for future usage.
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The L, R, S, and Y bits are set when the PCE can act as a PCE for
intra-area, inter-area, inter-AS or inter-layer TE LSPs computation
respectively. These bits are non-exclusive.
When set the Rd bit indicates that the PCE can act as a default PCE
for inter-area TE LSP computation (that is the PCE can compute a path
towards any neighbor area). Similarly, when set, the Sd bit indicates
that the PCE can act as a default PCE for inter-AS TE LSP computation
(the PCE can compute a path towards any neighbor AS).
When the Rd and Sd bit are set, the PCED sub-TLV MUST NOT contain any
NEIG-PCE-DOMAIN sub-TLV (see 4.1.4).
When the R/S bit is cleared, the Rd/Sd bit SHOULD be cleared and MUST
be ignored.
The PrefL, PrefR, PrefS and PrefY fields are each three bits long and
allow the PCE to specify a preference for each computation scope,
where 7 reflects the highest preference. Such preference can be used
for weighted load balancing of requests. An operator may decide to
configure a preference for each computation scope to each PCE so as
to balance the path computation load among them. The algorithms used
by a PCC to balance its path computation requests according to such
PCE preference are out of the scope of this document and is a matter
for local or network wide policy. The same or distinct preferences
may be used for each 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 bit or Y bit are cleared the PrefL, PrefR,
PrefS, PrefY fields SHOULD respectively be set to 0 and MUST be
ignored.
Both reserved fields SHOULD be set to zero on transmission and MUST
be ignored on receipt.
4.3. PCE-DOMAIN Sub-TLV
The PCE-DOMAIN sub-TLV specifies a PCE-Domain (areas and/or ASes)
where the PCE has topology visibility and through which the PCE can
compute paths.
The PCE-DOMAIN sub-TLV MAY be present when PCE-Domains cannot be
inferred by other IGP information, for instance when the PCE is
inter-domain capable (i.e. when the R bit or S bit is set) and the
flooding scope is the entire routing domain (see section 5 for a
discussion of how the flooding scope is set and interpreted).
A PCED sub-TLV MAY include multiple PCE-DOMAIN sub-TLVs when the PCE
has visibility in multiple PCE-Domains.
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The PCE-DOMAIN sub-TLV has the following format:
TYPE: 3
LENGTH: Variable
VALUE: This is comprised of one octet indicating the domain-type
(area ID or AS Number) and a variable length IS-IS area ID or a 32
bits AS number, identifying a PCE-domain where the PCE has visibility.
Two domain types are defined:
1 Area ID
2 AS Number
The Area ID is the area address as defined in [ISO].
When coded in two octets (which is the current defined format as the
time of writing this document), the AS Number field MUST have its
left two octets set to 0.
4.4. NEIG-PCE-DOMAIN Sub-TLV
The NEIG-PCE-DOMAIN sub-TLV specifies a neighbour PCE-domain (area,
AS) toward which a PCE can compute paths. It means that the PCE can
take part in the computation of inter-domain TE LSPs whose path
transits this neighbour PCE-domain.
A PCED sub-TLV MAY include several NEIG-PCE-DOMAIN sub-TLVs when the
PCE can compute paths towards several neighbour PCE-domains.
The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN
sub-TLV:
TYPE: 4
LENGTH: Variable
VALUE: This comprises one octet indicating the domain-type (area ID
or AS Number) and a variable length IS-IS area ID or a 32 bits AS
number, identifying a PCE-domain towards which the PCE can compute
paths.
Two domain types are defined:
1 Area ID
2 AS Number
The Area ID is the area address as defined in [ISO].
When coded in two octets (which is the current defined format as the
time of writing this document), the AS Number field MUST have its
first two octets set to 0.
The NEIG-PCE-DOMAIN sub-TLV MUST be present if the R bit is set and
the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is
cleared.
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4.5. PCE-CAP-FLAGS Sub-TLV
The PCE-CAP-FLAGs sub-TLV is an optional sub-TLV used to indicate
PCEP related capabilities. It MAY be present within the PCED sub-TLV.
It MUST NOT be present more than once. If it appears more than once
only the first occurrence MUST be processed and other MUST be ignored.
The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array
of units of 32 bit flags numbered from the most significant as bit
zero, where each bit represents one PCE capability.
The PCE-CAP-FLAGS sub-TLV has the following format:
TYPE: 5
LENGTH: Multiple of 4
VALUE: This contains an array of units of 32 bit flags numbered
from the most significant as bit zero, where each bit
represents one PCE capability.
The PCE capability registry is managed by IANA, it is common
with OSPF and defined in [PCED-OSPF].
Reserved bits SHOULD be set to zero on transmission and MUST be
ignored on receipt.
4.6. The OVERLOAD Sub-TLV
The OVERLOAD sub-TLV is used to indicate that a PCE is experiencing a
processing overload state and may optionally include expected PCE
overload duration.
The OVERLOAD sub-TLV is optional, it MAY be carried within the PCED
sub-TLV. It MUST NOT be present more than once. If it appears more
than once only the first occurrence MUST be processed and other MUST
be ignored.
The format of the OVERLOAD sub-TLV is as follows:
TYPE: 6
LENGTH: 1
VALUE: This comprises a one octet of bit flags indicating the
overload status. Currently only the first flag is defined.
Here is the TLV structure
+-+-+-+-+-+-+-+-+
|C| Reserved|
+-+-+-+-+-+-+-+-+
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Value
-C bit: When set this indicates that the PCE is overloaded
and cannot accept any new request. When cleared this
indicates that the PCE is not overloaded and can
accept new requests.
5. Elements of Procedure
The PCED sub-TLV is advertised within an IS-IS Router Capability TLV
defined in [IS-IS-CAP]. As such, elements of procedures are inherited
from those defined in [IS-IS-CAP].
The flooding scope is controlled by the S flag in the IS-IS Router
Capability TLV (see [IS-IS-CAP]). When the scope of the PCED sub-TLV
is area local it MUST be carried within an IS-IS Router Capability
TLV having the S bit cleared. When the scope of the PCED sub-TLV is
the entire IS-IS routing domain, it MUST be carried within an IS-IS
Router 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 area
local.
Note that a L1L2 node may include both in its L1 and L2 LSPs a PCED
TLV in a Router Capability TLV with the S bit cleared. This allows
restricting the flooding scope to the L1 area and the L2 sub-domain.
An IS-IS router MUST originate a new IS-IS LSP whenever there is a
change in a PCED TLV associated with a PCE it advertises.
When a PCE is deactivated, the IS-IS Router advertising this PCE MUST
originate a new IS-IS LSP that no longer includes the corresponding
PCED TLV.
The PCE address(s), i.e. the address(s) indicated within the PCE
ADDRESS sub-TLV, SHOULD be reachable via some prefix(es) advertised
by IS-IS; this allows speeding up the detection of a PCE failure.
Note that when the PCE address is no longer reachable, this means
that the PCE node has failed or has been torn down, or that there is
no longer IP connectivity to the PCE node.
A change in PCED information MUST not trigger any SPF computation at
a receiving router.
The way PCEs determine the information they advertise is out of the
scope of this document. Some information may be configured (e.g.,
address, preferences, scope) and other information may be
automatically determined by the PCE (e.g. areas of visibility).
5.1. OVERLOAD Sub-TLV Specific Procedures
When a PCE enters into an overload state, the conditions of which are
implementation dependent, a new IS-IS LSP with an OVERLOAD sub-TLV
with the C bit set MAY be generated.
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When a PCE exists from an overload state, the conditions of which are
implementation dependent (e.g. CPU utilization, average queue length
below some pre-defined thresholds), a new IS-IS LSP with an OVERLOAD
sub-TLV with the C bit cleared SHOULD be generated, if an OVERLOAD
sub-TLV with the C bit set had previously been generated.
A PCE implementation supporting the IS-IS extensions defined in this
document SHOULD support an appropriate dampening algorithm so as to
dampen flooding of PCE Overload information in order to not impact
the IS-IS scalability. It is RECOMMENDED to introduce some hysteresis
for overload state transition, so as to avoid state oscillations that
may impact IS-IS performance. For instance two thresholds MAY be
configured: an upper-threshold and a lower-threshold. An LSR enters
the overload state when the CPU load reaches the upper threshold and
leaves the overload state when the CPU load goes under the lower
threshold.
Upon receipt of an updated OVERLOAD sub-TLV a PCC should take
appropriate actions. In particular, the PCC SHOULD stop sending
requests to an overloaded PCE, and SHOULD gradually start sending
again requests to a PCE that is no longer overloaded.
6. Backward Compatibility
The PCED sub-TLV defined in this document does not introduce any
interoperability issues.
An IS-IS router not supporting the PCED sub-TLV will just silently
ignore the TLV as specified in [IS-IS-CAP].
7. IANA Considerations
Once a registry for the IS-IS Router Capability sub-TLVs, defined in
[IS-IS-CAP] has been assigned, IANA will assign a new sub-TLV code-
point for the PCED sub-TLV carried within the Router Capability TLV.
Value Sub-TLV References
----- -------- ----------
5 PCED sub-TLV (this document)
8. Security Considerations
This document defines IS-IS extensions for PCE discovery within an
administrative domain. Hence the security of the PCE discovery relies
on the security of IS-IS.
Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs
[RFC3567], and their TLVs, can be used to secure the PCED sub-TLV as
well.
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IS-IS provides no encryption mechanism for protecting the privacy of
LSPs, and in particular the privacy of the PCE discovery information.
9. Manageability Considerations
Manageability considerations for PCE Discovery are addressed in
section 4.10 of [RFC4674].
9.1. Control of Policy and Functions
Requirements on the configuration of PCE discovery parameters on PCCs
and PCEs are discussed in section 4.10.1 of [RFC4674].
Particularly, a PCE implementation SHOULD allow configuring the
following parameters on the PCE:
-The PCE IPv4/IPv6 address(es) (see section 4.1.1)
-The PCE Scope, including the inter-domain functions (inter-
area, inter-AS, inter-layer), the preferences, and whether the
PCE can act as default PCE (see section 4.1.2)
-The PCE domains (see section 4.1.3)
-The neighbour PCE domains (see section 4.1.4)
-The PCE capabilities (see section 4.1.5)
9.2. Information and Data Model
A MIB module for PCE Discovery is defined in [PCED-MIB].
9.3. Liveness Detection and Monitoring
PCE Discovery Protocol liveness detection relies upon IS-IS liveness
detection. IS-IS already includes a liveness detection mechanism
(Hello PDUs), and PCE discovery does not require additional
capabilities.
Procedures defined in section 5.1 allow a PCC detecting when a PCE
has been deactivated, or is no longer reachable.
9.4. Verify Correct Operations
The correlation of information advertised against information
received can be achieved by comparing the PCED information in the PCC
and in the PCE, which is stored in the PCED MIB [PCED-MIB]. The
number of dropped, corrupt, and rejected information elements are
stored in the PCED MIB.
9.5. Requirements on Other Protocols and Functional Components
The IS-IS extensions defined in this document do not imply any
requirement on other protocols.
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9.6. Impact on Network Operations
Frequent changes in PCE information, and particularly in PCE overload
information, may have a significant impact on IS-IS and might
destabilize the operation of the network by causing the PCCs to swap
between PCEs.
As discussed in section 5.1, a PCE implementation SHOULD support an
appropriate dampening algorithm so as to dampen IS-IS flooding in
order to not impact the IS-IS scalability.
Also, as discussed in section 4.10.4 of [RFC4674], it MUST be
possible to apply at least the following controls:
- Configurable limit on the rate of announcement of changed
parameters at a PCE.
- Control of the impact on PCCs such as through discovery messages
rate-limiting.
- Configurable control of triggers that cause a PCC to swap to
another PCE.
10. Acknowledgments
We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike
Shand, Lou Berger, and David Ward, for their useful comments and
suggestions.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ISO] "Intermediate System to Intermediate System Intra-Domain
Routeing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network Service
(ISO 8473)", ISO DP 10589, February 1990.
[RFC3784] 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.
[RFC3567] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567,
July 2003.
[PCED-OSPF] Le Roux, Vasseur, et al. "OSPF protocol extensions for
Path Computation Element (PCE) Discovery", draft-ietf-pce-disco-
proto-ospf, work in progress.
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Internet Draft draft-ietf-pce-disco-proto-isis-07.txt September 2007
11.2. Informative References
[RFC4657] Ash, J., Le Roux, J.L., "PCE Communication Protocol Generic
Requirements", RFC4657, September 2006.
[PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1", draft-ietf-pce-pcep, work
in progress.
[PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path
Computation Element Discovery", draft-ietf-pce-disc-mib, work in
progress.
[RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE)-based Architecture", RFC4655, august 2006.
[RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
RFC4674, October 2006.
12. Editors' Addresses:
Jean-Louis Le Roux (Editor)
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@orange-ftgroup.com
Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc.
1414 Massachusetts avenue
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
13. Contributors' Adresses:
Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
JAPAN
Email: y.ikejiri@ntt.com
Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA
Email: raymond_zhang@bt-infonet.com
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