PCE Working Group D. King Internet Draft Old Dog Consulting Intended status: Informational Created: March 1, 2010 Expires: September 1, 2010 Applicability of the Path Computation Element to Inter-Area and Inter-AS MPLS and GMPLS Traffic Engineering draft-king-pce-inter-area-as-applicability-00 Abstract The Path Computation Element (PCE) may be used for computing services that traverse multi-area and multi-AS Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineered (TE) networks. This document examines the applicability of the PCE architecture, protocols, and protocol extensions for computing multi-area and multi-AS paths in MPLS and GMPLS networks. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on September 1, 2010. King. Expires September 1, 2010 [Page 1] Internet-Draft March 2010 Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This Internet-Draft will expire on September 1, 2010. Table of Contents 1. Introduction.................................................. 1.1. Domains..................................................... 1.3. Path Computation............................................ 1.3. Traffic Engineering Aggregation and Abstraction............. 1.4. Traffic Engineered Label Switched Paths..................... 1.5. Inter-area and Inter AS Connectivity Discovery.............. 2. Terminology................................................... 3. Issues and Considerations..................................... 3.1 Multi-homed domains....................................... 3.2 Domain meshes............................................. 3.4 Destination location...................................... 4. Applicability of the PCE to Inter-area Traffic Engineering.... 4.1. Inter-area Routing....................................... 4.1.1. Area Inclusion and Exclusion........................... 4.1.2. Strict Explicit Path and Loose Path.................... 4.1.3. Inter-Area Diverse Path Computation.................... 4.2. Control and Recording of Area Crossing................... 4.3. Inter-Area Policies ..................................... 4.4. Loop Avoidance .......................................... 5. Applicability of the PCE to Inter-AS Traffic Engineering...... 5.1. Inter-AS Routing......................................... 4.1.1. AS Inclusion and Exclusion............................. 4.1.2. Strict Explicit Path and Loose Path.................... 5.1.3. AS Inclusion and Exclusion............................. 5.2. Inter-AS Bandwidth Guarantees............................ 5.3. Inter-AS Recovery........................................ 5.4. Inter-AS PCE Peering Policies............................ 6. Multi-Domain PCE Deployment................................... 6.1 Overview of Techniques.................................... 6.2 Traffic Engineering Database.............................. 6.3 Provisioning Techniques................................... King. Expires September 1, 2010 [Page 2] Internet-Draft March 2010 6.4 Pre-Planning and Management-Based Solutions............... 6.5 Per-Domain Computation.................................... 6.6 Cooperative PCEs.......................................... 6.7 Hierarchical PCEs ....................................... 7. Domain Topologies............................................. 7.1 Selecting Domain Paths.................................... 7.2 Multi-Homed Domains....................................... 7.3 Domain Meshes............................................. 7.4 Route Diversity........................................... 7.5 Synchronized Path Computations............................ 8. Domain Confidentiality........................................ 8.1 Loose Hops................................................ 8.2 Confidential Path Segments and Path Keys.................. 9. Point-to-Multipoint........................................... 10. Optical Domains.............................................. 10.1. Overview of Optical Domains................................ 11.1. Policy Control............................................. 11.1.1 Inter-AS PCE Peering Policy Controls...................... 12. IANA Considerations.......................................... 13. References................................................... 13.1. Normative References....................................... 13.2. Informative References..................................... 14. Acknowledgements............................................. 15. Author's Address............................................. 1. Introduction Computing paths across large multi-domain environments may require special computational components and cooperation between entities in different domains capable of complex path computation. The Path Computation Element (PCE) [RFC4655] provides an architecture and functional components to address this problem space. Computing optimal routes for LSPs that cross domains in MPLS-TE and GMPLS networks presents a problem because no single point of path computation is aware of all of the links and resources in each domain. A solution may be achieved using the PCE architecture [RFC4655]. A domain can be defined as a separate administrative, geographic, or switching environment within the network. A domain may be further defined as a zone of routing or computational ability. Under these definitions a domain might be categorized as an Antonymous System (AS) or an Interior Gateway Protocol (IGP) area [RFC4726] and [RFC4655]. King. Expires September 1, 2010 [Page 3] Internet-Draft March 2010 A PCE may be used to compute end-to-end paths across multi-domain environments using a per-domain path computation technique [RFC5152]. The backward recursive path computation (BRPC) mechanism [RFC5441]. Both per-domain and BRPC techniques assume that the sequence of domains to be crossed from source to destination is well known. In more advanced deployments (including multi-area and multi-AS environments) the sequence of domains may not be known in advance and the choice of domains in the end-to-end domain sequence might be critical to the determination of an optimal end-to-end path. In this case the use of the Hierarchical PCE [H-PCE] architecture and mechanisms may be used to discovery and select the optimal end-to-end domain sequence. This document examines the applicability and describes the processes and procedures available when using the PCE architecture, protocols and protocol extensions for computing inter-area and inter-AS MPLS Traffic Engineered paths. 1.1 Domains For the purposes of this document, a domain is considered to be a collection of network elements within an area or AS that has a common sphere of address management or path computational responsibility. Wholly or partially overlapping domains are not within the scope of this document. In the context of GMPLS, a particularly important example of a domain is the Automatically Switched Optical Network (ASON) subnetwork [G-8080]. In this case, computation of an end-to-end path requires the selection of nodes and links within a parent domain where some nodes may, in fact, be subnetworks. Furthermore, a domain might be an ASON routing area [G-7715]. A PCE may perform the path computation function of an ASON routing controller as described in [G-7715-2]. It is assumed that a PCE architecture should be applied to small inter-domain topologies and not solving route computation issues across large groups of domains, I.E. the entire Internet. 1.2 Path Computation For the purpose of this document it is assumed that the path computation is the sole responsibility of the PCE as per the architecture defined in [RFC4655]. When a path is required the Path Computation Client (PCC) will send a request to the PCE. The PCE will apply the required constraints and compute a path and return a response to the PCC. In the context of this document it maybe necessary for the PCE to co-operate with other PCEs in adjacent domains (as per BRPC [RFC5441]) or cooperate with the Parent PCE (as per [H-PCE]). King. Expires September 1, 2010 [Page 4] Internet-Draft March 2010 It is entirely feasible that an operator could compute a path across multiple domains without the use of a PCE if the relevant domain information is available to the network planner or network management platform. The definition of what relevant information is required to perform this network planning operation and how that information is discovered and applied is outside the scope of this document. 1.3 Traffic Engineering Aggregation and Abstraction Networks are often constructed from multiple areas or ASs that are interconnected via multiple interconnect points. To maintain network confidentiality and scalability TE properties of each area and AS are not generally advertized outside each specific area or AS. TE aggregation or abstraction provide mechanism to hide information but may cause failed path setups or the selection of suboptimal end-to-end paths [RFC4726]. The aggregation process may also have significant scaling issues for networks with many possible routes and multiple TE metrics. Flooding TE information breaks confidentiality and does not scale in the routing protocol. The PCE architecture and associated mechanisms provide a solution to avoid the use of TE aggregation and abstraction. 1.4 Traffic Engineered Label Switched Paths This document highlights the PCE techniques and mechanisms that exist for establishing TE packet and optical LSPs across multiple areas (inter-area TE LSP) and ASs (inter-AS TE LSP). In this context and within the remainder of this document, we consider all LSPs to be constraint-based and traffic engineered. Three signaling options are defined for setting up an inter-area or inter-AS LSP [RFC4726]: - Contiguous LSP - Stitched LSP - Nested LSP All three signaling methods are applicable to the architectures and procedures discussed in this document. 1.5 Inter-area and Inter AS Connectivity Discovery When using a PCE-based approach for inter-area and inter-AS path computation, a PCC in one area or AS may need to learn information related to inter-AS capable PCEs located in other ASs. The PCE discovery mechanism defined in [RFC5088] and [RFC5089] allow the discovery of PCEs and disclosure of information related to inter-area and inter-AS capable PCEs across area and AS boundaries. King. Expires September 1, 2010 [Page 5] Internet-Draft March 2010 2. Terminology Terminology used in this document. ABR: IGP Area Border Router, a router that is attached to more than one IGP area. 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 ASs or sub-ASs (BGP confederations LSP: Traffic Engineered Label Switched Path. LSR: Label Switching Router. TED: Traffic Engineering Database, which contains the topology and resource information of the domain. The TED may be fed by Interior Gateway Protocol (IGP) extensions or potentially by other means. This document also uses the terminology defined in [RFC4655] and [RFC5440]. 3. Issues and Considerations TBD. 3.1 Multi-homed domains 3.2 Domain meshes 3.4 Destination location 4. Applicability of the PCE to Inter-area Traffic Engineering As networks increase in size and complexity it may be required to introduce scaling methods to reduce the amount information flooded within the network and make the network more manageable. An IGP hierarchy is designed to improve IGP scalability by dividing the IGP domain into areas and limiting the flooding scope of topology information to within area boundaries. This restricts visibility of the area to routers in a single area. If a router needs to compute a route to destination located in another area a method is required to compute a path across area boundaries. King. Expires September 1, 2010 [Page 6] Internet-Draft March 2010 Per-domain path computation [RFC5152] exists to provide a method of inter-area path computation. The per-domain solution is based on loose hop routing with an Explicit Route Object (ERO) expansion on each Area Border Router (ABR). This allows an LSP to be established using a constrained path, however at least two issues exist: - This method does not guarantee an optimal constrained path - The method may require several crankback signaling messages increasing signaling traffic and delaying the LSP setup The PCE-based architecture [RFC4655] is designed to solve inter-area path computation problems. The issue of limited topology visibility is resolved by introducing path computation entities that are able to cooperate in order to establish LSPs with source and destinations located in different areas. 4.1. Inter-area Routing 4.1.1. Area Inclusion and Exclusion 4.1.2. Strict Explicit Path and Loose Path 4.1.3. Inter-Area Diverse Path Computation 4.2. Control and Recording of Area Crossing 4.3. Inter-Area Policies 4.4. Loop Avoidance 5. Applicability of the PCE to Inter-AS Traffic Engineering As discussed in section 4 (Applicability of the PCE to Inter-area Traffic Engineering) it is necessary to divide the network into smaller administrative domains, or ASes. If an LSR within an AS needs to compute a path across an AS boundary it must also use an inter-AS computation technique. RFC5152] defines mechanisms for the computation of inter-domain TE LSPs using network elements along the signaling paths to compute per-domain constrained path segments. The PCE was designed to be capable of computing MPLS and GMPLS paths across AS boundaries. This section outlines the features of a PCE-enabled solution for computing inter-AS paths. 5.1 Inter-AS Routing 5.1.1. AS Inclusion and Exclusion King. Expires September 1, 2010 [Page 7] Internet-Draft March 2010 5.1.2. Strict Explicit Path and Loose Path 5.1.3. AS Inclusion and Exclusion 5.2 Inter-AS Bandwidth Guarantees Many operators with multi-AS domains will have deployed MPLS-TE Diffserv either across their entire network or at the domain edges on CE-PE links. In situations where strict QOS bounds are required, admission control inside the network may also be required. When the propagation delay can be bounded, the performance targets, such as maximum one-way transit delay may be guaranteed by providing bandwidth guarantees along the Diffserv-enabled path. One typical example of this requirement is to provide bandwidth guarantees over an end-to-end path for VoIP traffic classified as EF (Expedited Forwarding) class in a Diffserv-enabled network. In the case where the EF path is extended across multiple ASes, inter-AS bandwidth guarantee would be required. Another case for inter-AS bandwidth guarantee is the requirement for guaranteeing a certain amount of transit bandwidth across one or multiple ASes. 5.3 Inter-AS Recovery 5.4 Inter-AS PCE Peering Policies 6. Mult-domain PCE Deployment Options The PCE provides the architecture and mechanisms to compute inter-area and inter-AS LSPs. The objective of this document is not to reprint the techniques and mechanisms available, but to highlight their existence and reference the relevant documents that introduce and describe the techniques and mechanisms necessary for computing inter-area and inter-AS LSP based services. An area or AS may contain multiple PCEs: - The path computation load may be balanced among a set of PCEs to improve scalability. - For the purpose of redundancy, primary and backup PCEs may be used. - PCEs may have distinct path computation capabilities (P2P or P2MP). Discovery of PCEs and capabilities per area or AS is defined in in [RFC5088] and [RFC5089]. King. Expires September 1, 2010 [Page 8] Internet-Draft March 2010 Each PCE per domain can be deployed in a centralized or distributed architecture, the latter model having local visibility and collaborating in a distributed fashion to compute a path across the domain. Each PCE may collect topology and TE information from the same sources as the LSR, such as the IGP TED. When the PCC sends a path computation request to the PCE, the PCE will compute the path across a domain based on the required constraints. The PCE will generate the full set of strict hops from source to destination. This information, encoded as an ERO, is then sent back to the PCC that requested the path. In the event that a path request from a PCC contains source and destination nodes that are located in different domains the PCE is required to co-operate between multiple PCEs, each responsible for its own domain. Techniques for inter-domain path computation are described in [RFC5152] and [RFC5441], both techniques assume that the sequence of domains to be crossed from source to destination is well known. In the event that the sequence of domains is not well known, [H-PCE] might be used. 6.1 Overview of Techniques 6.2 Traffic Engineering Database 6.3 Provisioning Techniques 6.4 Pre-Planning and Management-Based Solutions Offline path computation is performed ahead of time, before the LSP setup is requested. That means that it is requested by, or performed as part of, a management application. This model can be seen in Section 5.5 of [RFC4655]. The offline model is particularly appropriate to long-lived LSPs (such as those present in a transport network) or for planned responses to network failures. In these scenarios, more planning is normally a feature of LSP provisioning. This model may also be used where the network operator wishes to retain full manual control of the placement of LSPs, using the PCE only as a computation tool to assist the operator, not as part of an automated network. 6.5 Per-Domain Computation 6.6 Cooperative PCEs 6.7 Hierarchical PCEs King. Expires September 1, 2010 [Page 9] Internet-Draft March 2010 7. Domain Topologies TBD. 7.1 Selecting Domain Paths 7.2 Multi-Homed Domains 7.3 Domain Meshes 7.4 Route Diversity 7.5 Synchronized Path Computations 8. Domain Confidentiality TBD 8.1 Loose Hops 8.2 Confidential Path Segments and Path Keys 9. Point-to-Multipoint TBD. 10. Optical Domains TBD. 10.1. Overview of Optical Domains 11. Security TBD 11.1. Policy Control 11.1.1 Inter-AS PCE Peering Policy Controls Each PCE cooperating with another PCE in a neighboring AS will need to request or enforce policies applicable to the sender of the request. King. Expires September 1, 2010 [Page 10] Internet-Draft March 2010 Parameters that are subject to policy include bandwidth, setup/holding priority, Fast Reroute request, Differentiated Services Traffic Engineering (DS-TE) Class Type (CT), and others as specified in Section 5.2.2.1 of [RFC4216]. 11.2. Confidentiality 11.3. Denial of Service Attacks 12. IANA Considerations This document makes no requests for IANA action. 13. References 13.1. Normative References [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. [RFC5440] Ayyangar, A., Farrel, A., Oki, E., Atlas, A., Dolganow, A., Ikejiri, Y., Kumaki, K., Vasseur, J., and J. Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. 13.2. Informative References [RFC4216] Zhang, R., Ed., and J.-P. Vasseur, Ed., "MPLS Inter- Autonomous System (AS) Traffic Engineering (TE) Requirements", RFC 4216, November 2005. [RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for Inter-Domain Multiprotocol Label Switching Traffic Engineering", RFC 4726, November 2006. [RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang, "OSPF Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5088, January 2008. [RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R. Zhang, "IS-IS Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5089, January 2008. [RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain Path Computation Method for Establishing Inter-Domain Traffic Engineering (TE) Label Switched Paths (LSPs)", RFC 5152, February 2008. King. Expires September 1, 2010 [Page 11] Internet-Draft March 2010 [RFC5441] Vasseur, J.P., Ed., "A Backward Recursive PCE-based Computation (BRPC) procedure to compute shortest inter- domain Traffic Engineering Label Switched Paths", RFC5441, April 2009. [G-8080] ITU-T Recommendation G.8080/Y.1304, Architecture for the automatically switched optical network (ASON). [G-7715] ITU-T Recommendation G.7715 (2002), Architecture and Requirements for the Automatically Switched Optical Network (ASON). [G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON routing architecture and requirements for remote route query. [H-PCE] King, D. and A. Farrel, "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS & GMPLS", December 2009. 11. Acknowledgements The author would like to thank Adrian Farrel for his review and comments. 12. Author's Address Daniel King Old Dog Consulting UK Email: daniel@olddog.co.uk King. 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