Network Working Group Y.L. Bao
Internet-Draft X.H. Fu
Intended status: Informational G. Xie
Expires: April 22, 2010 ZTE Corporation
October 19, 2009
A Path Computation Element (PCE) Application for Pre-configured Routing
draft-bao-pce-pre-configured-routing-00
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Abstract
Pre-configured routing is a routing scheme that except primary route
operator configures one or multiple routes which will be used as
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recovery route when the primary route fails for a service previously.
This document improves this traditional routing shceme, and PCE (Paht
Computation Element) is applied for pre-configured routing.
Furthermore, this document also presents a detailed set of PCC-PCE
(Path Computation Client) communication protocol requirements and
defines PCEP (Path Computation Element Communication Protocol)
extensions for PCEP.
Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Application of pre-configured Routing . . . . . . . . . . . . . 3
4. Architecture Analysis and Requirement . . . . . . . . . . . . . 4
4.1. Architecture Analysis . . . . . . . . . . . . . . . . . . . 4
4.2. Requirements to PCE . . . . . . . . . . . . . . . . . . . . 5
4.3. Requirements to PCEP . . . . . . . . . . . . . . . . . . . 5
5. Extensions to PCEP and Procedures . . . . . . . . . . . . . . . 6
5.1. New Flag Of The LSPA Object . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7.1. New Flag Of The LSPA Object . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. 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].
2. Introduction
Pre-configured routing is a very useful approach to achieve service
resteration. Generally, except primary route, operator also sets a
group of routes (usually with priority), i.e. pre-configured route
set,for a service. When the primary route fails, router can select a
proper resteration route from pre-configured route set. By this way,
faster resteration can be achieved.
Since pre-configured routes are pre-configured by management plane,
it can't be updated when network state changes dynamically. In some
cases, e.g. a fiber on the pre-configured route is cut, if operator
can't update pre-configured routes in time, the pre-configured routes
will become unavailable. Otherwise, generally the pre-configured
routes will be verified whether it is available before it is used to
signal a connection. This is also due to the problem that pre-
configured routes can't be updated timely. So this will introduce
another problem that time delay will affect service recovery.
This document introduces a PCE-based pre-configured routing method,
which uses PCE to update pre-configured route at the policy of
network management. This method helps to optimize network resources
and avoid the unavailablity of pre-configured routes.
3. Application of pre-configured Routing
As illustrated in figure 1, an example network is comprised of 9
nodes and an external PCE. Suppose there is a service between A and
I. In order to create the connection, source node A request a working
path. And PCE responds node A with path A-D-I. However, to provide
fast recovery when primary path A-D-I fails, node A can also request
additional pre-configured routes. And PCE reponds with path A-B-C-I
and A-E-F-G-H-I providing node A requested 2 pre-configured routes.
To provide the availability of pre-configured routes, PCE can
dynamically upade these routes according to the local policy. For
example, PCE can be configured to update Pre-configured route when
network status changes, or a 30 seconds timer expires etc.
In figure 1, Assume PCE is configured to update pre-configured route
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as network status changes, when link BC failed, PCE will
aucomatically compute and send route A-B-D-I to source node A to
refresh previously requested pre-configured route.
If primary path fails, e.g. the fiber on link AD is cut, node A can
use pre-configured route A-B-C-I to recovery service between A and I
without requesting PCE again.
+=====+
| PCE |
+=====+
+---+ +---+
.--------+ B +----------+ C +
/ +-+-+ +-+-+
/ \ \
/ \ `--------.
/ \ \
+-+-+ +-+-+ +-+-+
| A +---------------+ D +-------------------+ I |
+-+-+ +-+-+ +-+-+
\ / /
\ / /
\ / /
+-+-+ +-+-+ +-+-+ +-+-+
| E +-------+ F +-------+ G +-------+ H |
+---+ +---+ +---+ +---+
Figure 1: Example of Application of Pre-configured Routing
4. Architecture Analysis and Requirement
4.1. Architecture Analysis
[RFC4655] introduced 5 PCE models which can be categorized according
to whether PCE functionality is integrated into the network element.
Under this methodology, two groups of PCE model, i.e. composite PCE
and external PCE, is generated.
For composite PCE, due to the resource limitation of the card, the
power of CPU is relatively weak, so the PCE capability is also
limited. However, compared to composite PCE, external PCE has more
resources (i.e. memory and CPU power etc), and it even can be
presented as a dedicated server. Therefore, external PCE is more
powerful than composite PCE. The application of pre-configured
routing will increase compuataion burden to PCE. Due to its powerful
computation capability, external PCE is more adequate than composite
PCE. However, if there is not much application of pre-configured
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routing, composite PCE can also operate well.
[RFC4655] also describes stateful PCE and stateless PCE. For
statefull PCE, there is a strict synchronization between the PCE and
not only the network states (in term of topology and resource
information), but also the set of computed paths and reserved
resources in use in the network. So, it is easier to applying pre-
configured routing on stateful PCE.
Furthermore, considering the PCE failure, if an implementation has a
backup PCE, then the primary and backup PCE MUST keep strict
synchronization. And switching to the backup PCE can't affect the
correctness of path computation
However, the selection of PCE model, stateful PCE or stateless PCE is
out of this document. And the synchronizt between primary and backup
PCE is also out of this document, the operator can make a selection
according to network deployment.
4.2. Requirements to PCE
In order to support pre-configured routing, PCE SHOULD record pre-
configured route information, and maintain its status. When network
status changes, PCE SHOULD compute the affected pre-configured
routes. However, PCE MAY also compute pre-configured routes in idle
state to obtain the optimized pathes. The policy for PCE compute
pre-configured routes SHOULD be able to configured.
4.3. Requirements to PCEP
[RFC4657] gives detailed generic requirements for PCE communication
protocol. However, in orderto support pre-configured routing,
specific extensions to PCEP is required. For PCReq, it SHOULD be
possible for PCC to request pre-configured route. When PCE receives
a request identified with pre-configured routing, it SHOULD perform
path computation accroding to the required policy, e.g. node
disjoint, link disjoint and SRLG disjoint etc. And in the response
message, PCE SHOULD able to specify which one is pre-exsiting route.
If mulitple pre-configured routes are requested, PCE SHOULD give each
pre-configured route a priority in PCRep message. If PCE doesn't
support pre-configured routing it SHOULD give a negative response,
and the reason for computation failure.
When network status changes, PCE SHOULD re-compute pre-configured
routes according the configured policy. If new better pre-configured
route is computed, PCE should send it to PCC. There are two options
for PCE to send pre-configured route as follows:
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PCRep is used to respond route computation result naturally. If it
is used to send pre-configured route, a new flag SHOULD be defined to
indicate the route carried is pre-configured route.
5. Extensions to PCEP and Procedures
5.1. New Flag Of The LSPA Object
The LSPA (LSP Attributes defined in [RFC5440]) object specifies
various TE LSP attributes to be taken into account by the PCE during
path computation. The LSPA object can be carried within a PCReq
message, or a PCRep message.
In order to support pre-configured route in PCReq and PCRep message,
a new flag, Pre-Configured Route flag, is defined in LSPA (LSP
Attributes) object. The definition of Pre-Configured Route flag is:
Bit Number Name Flag
22 Pre-Configured Route
When PCC requests pre-configured route, it SHOULD set Pre-Configured
Route flag in LSPA object. And PCE SHOULD also set this flag, when
it sends computed pre-configured route to PCC. If PCE can't
recognize Pre-Configured Route flag, a PCErr message SHOULD be sent
with an Error-Type=2 (Capability not supported).
6. Security Considerations
This document has no requirement for a change to the security models
within PCEP and associated protocols.
7. IANA Considerations
7.1. New Flag Of The LSPA Object
A new flag of the LSPA object (specified in [RFC5440]) is defined in
this document.
Pre-Configured Route Flag
Bit Number Name Flag Reference
22 Pre-Configured Route This document
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8. Acknowledgements
The RFC text was produced using Marshall Rose's xml2rfc tool.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE)
Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
Authors' Addresses
Yuanlin Bao
ZTE Corporation
5F, R&D Building 3, ZTE Industrial Park, XiLi LiuXian Road
Nanshan District, Shenzhen 518055
P.R.China
Phone: +86 755 26773731
Email: bao.yuanlin@zte.com.cn
URI: http://www.zte.com.cn/
Xihua Fu
ZTE Corporation
West District,ZTE Plaza,No.10,Tangyan South Road,Gaoxin District
Xi An 710065
P.R.China
Phone: +8613798412242
Email: fu.xihua@zte.com.cn
URI: http://www.zte.com.cn/
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Gang Xie
ZTE Corporation
ZTE Plaza, No.19, Huayuan Road East, Haidian District
Bei Jing 100191
P.R.China
Phone: +8613798412242
Email: xie.gang@zte.com.cn
URI: http://www.zte.com.cn/
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