Internet DRAFT - draft-boucadair-pce-discovery
draft-boucadair-pce-discovery
PCE Working Group M. Boucadair (Ed.)
Internet Draft P. Morand (Ed.)
France Telecom R&D
Document: draft-boucadair-pce-discovery-01.txt May 2005
Category: Standards Track
Path Computation Service discovery via Border Gateway Protocol
< draft-boucadair-pce-discovery-01.txt >
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667 [RFC3667]. By submitting this Internet-
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Abstract
This draft describes a simple mechanism that ease discovery of remote
Autonomous Systems (AS) supporting inter-domain MPLS-based
constrained tunnels service (this service is also denoted by Path
Computation Service (PCSv)) thanks to the use of Path Computation
Elements (PCEs). Remote ASs could be managed by a single or distinct
Internet Network Providers (INP).
Particularly, this draft describes how Border Gateway Protocol (BGP)
is used to announce Path Computation Service unique identifiers
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across the Internet in order for other PCEs to be able to discover a
path towards every AS supporting this Path Computation Service.
Table of Contents
1. Contributors................................................2
2. Changes since last version:.................................2
3. Terminology.................................................2
4. Introduction................................................3
4.1. General.....................................................3
4.2. Structure of the draft......................................4
5. Conventions used in this document...........................4
6. PCE discovery within a single domain........................5
7. Overview of the service approach............................5
8. Service Advertisement and Discovery.........................6
9. Why PCE discovery is needed.................................7
10. Solution for PCSv discovery.................................7
11. IANA Considerations.........................................8
12. Security Considerations.....................................8
13. References..................................................9
14. Acknowledgments.............................................9
15. Author's Addresses.........................................10
1. Contributors
o Hamid Asgari (Thales Research and Technology)
o Panagiotis Georgatsos (Algonet)
o David Griffin (University College London)
o Micheal Howarth (University of Surrey)
o Noel Cantenot (France Telecom)
2. Changes since last version:
The main changes occurred in this version are:
o Rewording of several sections of the draft
3. Terminology
This memo makes use of the following terms:
o Path Computation Element (PCE): an entity that is responsible
for computing/finding inter/intra domain paths for establishing
LSPs. This entity can simultaneously act as client and a server.
Several PCEs could be deployed in a given AS.
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o Path Computation Client (PCC): a PCE acting as a client. This
entity is responsible for issuing path computation requests that
fulfill the Service Management constraints for the establishment
of inter/intra domain LSPs.
o Path Computation Server (PCS): a PCE acting as a server. This
entity is responsible for handling path computation requests in
order to satisfy PCC constraints.
o High-level service: is the service using a PCE-based system as
an underlying infrastructure (an inter-domain QoS VPNs service
for instance)
o High-level service customer: is a customer that subscribes to a
High-level service.
o pSLS: A provider SLS is an SLS established between two Internet
Network Providers (INP) with the purpose of extending the
geographical span of their service offers.
o SLS Management: This management entity is responsible for SLS-
related activites, including pSLS ordering (i.e establishing
contracts between peers) and SLS invocation (i.e committing
resources before traffic can be admitted)
o q-BGP: QoS-inferred BGP. A modified BGP protocol that takes into
account QoS information as input for its route selection
process.
o Domain: within this draft it denotes an Autonomous system.
4. Introduction
4.1. General
Recently, several proposals describing the use of a Path Computation
Element (PCE) as additional element to existent IP network entities
have been submitted to the IETF. The main objective of introducing a
PCE element is to ease computation of constrained paths in
sophisticated schemes like inter-domain (both in intra-provider or
inter-provider) and then driving the establishment of inter-domain
LSPs.
A framework for establishing and controlling Multi-Protocol Label
Switching Protocol (MPLS) and Generalized MPLS (GMPLS) Label
Switching Paths (LSPs) in multi-domain networks has been defined in
[CCAMP-FWRK]. The notion of domain in this framework draft encloses
both Interior Gateway Protocol (IGP) areas and Autonomous System (AS)
contrary to the current draft that restricts the notion of domain to
a single AS.
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Another draft that proposes a solution to compute inter-domain
constrained paths has been submitted to the IETF [INTERAS-PCE]. This
draft takes into account the inter-provider specific service
considerations. In addition, the draft [INTERAS-PCP] describes a new
protocol allowing communication between two PCEs located in different
domains in order to compute inter-domain paths satisfying a set of
constraints.
All aforementioned drafts require a Path Computation Service (PCSv)
discovery function that allows discovery of remote ASs supporting
this type of service (the path computation service could be
implemented by one or several PCE elements) together with theirs
associated capabilities like
QoS capabilities, inter-domain bandwidth, reachable IP prefixes, type
of links, etc. Discovery of such capabilities could also be passive
and be restricted to a simple service advertisement (like web-pages).
PCSv locations and associated capabilities discovery depends on
providers search. We will refer to this method as passive discovery
method.
It is evident that passive method allows finding remote PCSv
locations and their associated capabilities, but this information is
not usable alone within a distributed PCE architecture, when a set of
end-to-end constraints must be satisfied. Therefore, computation of
end-to-end constraints must be achieved based on advertised
individual PCE capabilities. The knowledge of the PCE path is then
mandatory in order to deduce the end-to-end capabilities.
In this draft, we present a simple method that allows discovery of
remote PCSv with their associated capabilities. This method will also
help the PCE decision-making process to choose the next PCE to
contact in order to optimize paths towards a given destination.
4.2. Structure of the draft
This draft is structured as follows:
o Section 5 gives an overview of the service approach;
o Section 6 argues on the need of PCSv discovery functions;
o Section 7 presents a solution proposal for PCSv discovery.
5. 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 [RFC2119].
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6. PCE discovery within a single domain
Within a single domain, discovery of PCSv location and capabilities
could be achieved for instance thanks to the activation of the
Service Location Protocol (SLP, [RFC2608]). This protocol allows
discovery of activated services that uses client/service
architecture. SLP defines the same framework for all services.
In order to use SLP as a means to discover PCSvs, a PCE Service Type
Template SHOULD be defined.
7. Overview of the service approach
Neighboring domains establish pSLSs (a pSLS is an enhanced SLS
agreement between two providers. SLS template is defined in [SLS])
between them in order to have appropriate rights to request
establishment of LSPs. An inter-domain routing protocol runs between
the domains (for instance Border Gateway Protocol (BGP, [RFC1771])).
The LSP creation request is propagated downstream to appropriate
PCEs. The requests include the AS's ASBR and the tail-end address of
the LSP. This procedure is repeated until the request reaches the
destination PCE.
+--------High Level Service Agreement--------+
| |
v v
<----AS1-----> <----AS2-----> <----AS3----->
' ' ' ' ' '
' '<-pSLS->' '<- pSLS->' '
' ' ' ' ' '
+------------+ +------------+ +------------+
| PCE | | PCE | | PCE |
| | | | | |
| +------+ | | +------+ | | +------+ |
| | PCC | | | | PCC | | | | PCC | |
| | |<-|--\ | | |<-|--\ | | | |
| +--/\--+ | | | +--/\--+ | | | +--/\--+ |
| || | |PCP | || | |PCP | || |
| || | | | || | | | || |
| +--\/--+ | | | +--\/--+ | | | +--\/--+ |
| | PCS | | \-----|->| PCS | | \------|->| PCS | |
| | | | | | | | | | | |
| +------+ | | +------+ | | +------+ |
+------------+ +------------+ +------------+
Figure 1: Service Overview
After authenticating the identity of LSP originating PCE, the
destination PCE send a reply message back to the downstream domain's
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PCE accepting the request and include the LSP loose path
(destination, ASBR) addresses in the message. The next downstream
domain's PCE does the same and adds its own relevant ASBR addresses
to the loose path. The originating PCE inserts its intra-domain path
and then initializes an RSVP reservation request for LSP
establishment using the returned loose path.
At the service/application level (in order to differentiate this
service from extending scope of IP connectivity service, we will
denote it as high level service), when originating AS wants to
establish an LSP to a destination in a remote ASs, there MUST be an
agreement between the two ASs.
8. Service Advertisement and Discovery
Within this draft, we make a difference between the Service
Advertisement and Discovery (SAD) and PCSv discovery function. SAD is
a function that is achieved before establishing a service agreement
between two peers. The SAD operation consists mainly at
advertising/learning from/to the rest of the Internet the
capabilities supported by a given AS in term of offered services
(like Inter-domain LSP establishment service). PCSv advertisement is
conditioned by the existence of a pSLS between two peers.
AS1 ' AS2
'
+----------------------+ '
|Service Advertisement |<---'-------------------\
+----------------------+ ' |
' |
+----------v-----------+
| Service Discovery |
+----------------------+
' |
' |
+----------v-----------+
| Service Planning |
+----------------------+
|
+----------------------+ ' +----------v-----------+
|Service Negotiation |<---'------->|Service Negotiation |
+----------------------+ ' +----------------------+
Figure 2: Service Advertisement and Discovery
Local Service Discovery block is responsible for finding remote
offered services that is an essential input for Service Planning
block. This functional block is responsible for choosing from
discovered offered services the ones that will be used in order to
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build it own services. Thus, a negotiation process SHOULD start and
an SLS MAY be agreed between the two parties.
During service negotiation between two Service Providers, they MAY
exchange their PCE reachability information and associated
capabilities. Theses capabilities could include the following:
o Supported Computation algorithms
o Types of Constraints (e.g. QoS)
o Set of attributes for a given constraint (one-way delay, one-way
delay variationà)
o Support of P2MP path computation techniques,
As a consequence each INP has a full knowledge of the PCE
capabilities of its adjacent providers.
9. Why PCE discovery is needed
Path Computation elements are responsible for finding inter-domain
paths satisfying a set of constraints (like QoS performance
guarantees) to establish inter-domain constraint-based LSPs. The
computation of this path is distributed and needs PCEs from different
domains to communicate. Communication between two PCE entities is
enabled thanks to inter PCE Communication Protocol (PCP) [INTERAS-
PCP].
When receiving a request from the "High-Level" Service Management to
compute/find a path towards a given tail-end address, the local PCE
has to determine the next PCE to contact. In the worst case, local
PCE can contact all its neighboring PCEs that are known to Service
Management System. Nevertheless, it has no criteria to choose between
those PCEs the next PCE to be contacted in order to send its path
computation request. The risk of a request failure is then important.
In order to help the PCE decision-making process to choose the next
PCE to be contacted, local PCE need to discover remote PCSvs
reachable beyond the immediate neighbor PCEs. This information will
help the next hop PCE decision. PCE need at least access to intra and
inter-domain Routing Information Bases (RIB) in order to check the
reachability status of destination prefixes if are propagated thanks
to routing protocols.
10. Solution for PCSv discovery
Within this draft, we assume that during service negotiation phase
between two peers, they MUST exchange IP addresses of their PCE(s).
SLS Management Systems of the two peers MUST store this information.
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In order to help the PCE computation process, routing information
MUST be made available for the PCE. Thus, reachability information
associated with capabilities (like QoS intra and/or inter-domain
capabilities) SHOULD be propagated in the routing level. In the case
of QoS-based service, each potential tail-end address (practically
all routers interfaces) SHOULD be announced in all offered QoS Class
plans (i.e. as many as used DSCP values). As a consequence, routing
tables sizes will drastically increase.
From this perspective, instead of announcing all potential tail-end
addresses in BGP, only an identifier needs to be announced. It is
called the Path Computation Service Identifier (PCSID). This
particular BGP announcement is identified by a well-known community
value (to be defined be IANA) and is represented by a routable IP
address, which can be different from the real IP address of the PCE.
As a consequence, this particular route SHOULD NOT be installed in
the Forwarding Information Base (FIB) since this PCSID is not
necessarily the IP address of the PCE.
BGP announcements of PCSID will ease to discover the set of remote
ASs supporting the inter-AS MPLS-based constrained tunnels service
together with their associated end-to-end capabilities for reaching
them. In order to compute a path towards a specific domain supporting
this inter-AS MPLS-based constrained tunnels service, the local PCE
chooses a route that serves the PCSID of that domain and extracts
from the AS_PATH attribute the AS number of the next hop ASBR. Then,
the local PCE queries its SLS Management system and gets back the
PCE's IP address of the next neighboring PCE to contact. Finally, the
local PCE forms and forwards a path computation request to this next
PCE. The process is iteratively repeated until the request reaches
the PCE of the target AS identified by its PCSID.
This solution decreases the number of BGP announcements that are
reduced to one announcement per AS.
11. IANA Considerations
The solution proposed in this draft uses a well-know community
attribute value that SHOULD be attributed by IANA [RFC2434] in order
to facilitate recognition of BGP announcements that announce PCSv and
associated capabilities.
12. Security Considerations
This additional draft does not change the underlying security issues
in the existing BGP-4 protocol specification [RFC2385].
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13. References
[RFC3667] Bradner, S., "IETF Rights in Contributions", RFC 3667,
February 2004
[RFC3668] Bradner, S., "Intellectual Property Rights in IETF
Technology", RFC 3668, February 2004
[CCAMP-FWRK] Farrel, A., Vasseur, JP., Ayyangar, A., "A Framework for
Inter-Domain MPLS Traffic Engineering", draft-ietf-ccamp-inter-
domain-framework-00.txt, August 2004
[INTERAS-PCE] Boucadair, M., Morand, P., "A Solution for providing
inter-AS QoS tunnels", draft-boucadair-pce-interas-01.txt, May
2005
[INTERAS-PCP] Boucadair M., Morand P. and al., "Inter-AS PCE
Communication Protocol", draft-boucadair-pcp-interas-01.txt, May
2005
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
[RFC2608] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service
Location Protocol, version 2", RFC 2608, July 1999
[SLS] Goderis D., T'Joens Y., Jacquenet C., Memenios G., Pavlou G.,
Egan R., Griffin D., Georgatsos P., Georgiadis L., Heuven P.V.,
"Service Level Specification Semantics and parameters", draft-
tequila-sls-02.txt, Work in progress.
[RFC1771] Rekhter, Y., Li T., "A Border Gateway Protocol 4 (BGP-4)",
RFC 1771, March 1995.
[RFC2434] Alvestrand, H. and T. Narten, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434, October
1998
[RFC2385] Heffernan, A., "Protection of BGP sessions via the TCP
MD5 Signature Option", RFC 2385, August 1998
14. Acknowledgments
Part of this work is funded by the European Commission, within the
context of the MESCAL (Management of End-to-End Quality of Service
Across the Internet At Large, http://www.mescal.org) project, which
is itself part of the IST (Information Society Technologies) research
program.
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The authors would also like to thank all the partners of the MESCAL
project for the fruitful discussions.
15. Author's Addresses
Mohamed Boucadair
France Telecom R & D
42, rue des Coutures
BP 6243
14066 Caen Cedex 4
France
Phone: +33 2 31 75 92 31
Email: mohamed.boucadair@francetelecom.com
Pierrick Morand
France Telecom R & D
42, rue des Coutures
BP 6243
14066 Caen Cedex 4
France
Email: pierick.morand@francetelecom.com
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