PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths
Author(s): Ramon Casellas, Zafar Ali, Dhruv Dhody, Quintin Zhao, Daniel King
The ability to compute paths for constrained point-to-multipoint (P2MP) Traffic Engineering Label Switched Paths (TE LSPs) across multiple domains has been identified as a key requirement for the deployment of P2MP services in MPLS and GMPLS-controlled networks. The...
PCE Working Group Q. Zhao Internet-Draft D. Dhody Intended status: Experimental Huawei Technology Expires: January 14, 2014 Z. Ali Cisco Systems D. King Old Dog Consulting R. Casellas CTTC - Centre Tecnologic de Telecomunicacions de Catalunya July 14, 2013 PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths draft-ietf-pce-pcep-inter-domain-p2mp-procedures-05 Abstract The ability to compute paths for constrained point-to-multipoint (P2MP) Traffic Engineering Label Switched Paths (TE LSPs) across multiple domains has been identified as a key requirement for the deployment of P2MP services in MPLS and GMPLS-controlled networks. The Path Computation Element (PCE) has been recognized as an appropriate technology for the determination of inter-domain paths of P2MP TE LSPs. This document describes an experiment to provide procedures and extensions to the PCE communication Protocol (PCEP) for the computation of inter-domain paths for P2MP TE LSPs. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on July 14, 2013. Zhao, et al. July 14, 2013 [Page 1] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 Copyright Notice Copyright (c) 2013 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Objective Functions and Constraints. . . . . . . . . . . . . . 8 7. P2MP Path Computation Procedures . . . . . . . . . . . . . . . 8 7.1. Core Trees . . . . . . . . . . . . . . . . . . . . . . . . 8 7.2. Core Tree Computation Procedures . . . . . . . . . . . . .10 7.3. Sub-tree Computation Procedures . . . . . . . . . . . . .11 7.4. PCEP Protocol Extensions . . . . . . . . . . . . . . . . .12 7.4.1. The Extension of RP Object . . . . . . . . . . . . . .12 7.4.2. Domain and PCE Sequence . . . . . . . . . . . . . . .12 7.5. Relationship with Hierarchical PCE . . . . . . . . . . . .13 7.6. Parallelism . . . . . . . . . . . . . . . . . . . . . . .13 8. Protection . . . . . . . . . . . . . . . . . . . . . . . . . .13 8.1. End-to-end Protection . . . . . . . . . . . . . . . . . .14 8.2. Domain Protection . . . . . . . . . . . . . . . . . . . .14 9. Manageability Considerations . . . . . . . . . . . . . . . . .14 9.1. Control of Function and Policy . . . . . . . . . . . . . .14 9.2. Information and Data Models . . . . . . . . . . . . . . .15 9.3. Liveness Detection and Monitoring . . . . . . . . . . . .15 9.4. Verifying Correct Operation . . . . . . . . . . . . . . .15 9.5. Requirements on Other Protocols and Functional Components . . . . . . . . . . . . . . . . . . . . . . . .15 9.6. Impact on Network Operation . . . . . . . . . . . . . . .16 9.7. Policy Control . . . . . . . . . . . . . . . . . . . . . .16 10. Security Considerations . . . . . . . . . . . . . . . . . . .16 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .17 Zhao, et al. July 14, 2013 [Page 2] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .17 13. References . . . . . . . . . . . . . . . . . . . . . . . . . .17 13.1. Normative References . . . . . . . . . . . . . . . . . . .17 13.2. Informative References . . . . . . . . . . . . . . . . . .17 14. Contributors' Addresses . . . . . . . . . . . . . . . . . . .19 15. Authors' Addresses . . . . . . . . . . . . . . . . . . . . .19 1. Introduction Multicast services are increasingly in demand for high-capacity applications such as multicast Virtual Private Networks (VPNs), IP- television (IPTV) which may be on-demand or streamed, and content- rich media distribution (for example, software distribution, financial streaming, or database-replication). The ability to compute constrained Traffic Engineering Label Switched Paths (TE LSPs) for point-to-multipoint (P2MP) LSPs in Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks across multiple domains are therefore required. The applicability of the Path Computation Element (PCE) [RFC4655] for the computation of such paths is discussed in [RFC5671], and the requirements placed on the PCE communications Protocol (PCEP) for this are given in [RFC5862]. This document details the requirements for inter-domain P2MP path computation, it then describes the experimental procedure "core-tree" path computation, developed to address the requirements and objectives for inter-domain P2MP path computation. 1.2. Scope The inter-domain P2MP path computation procedures described in this document is experimental. The experiment is intended to enable research for the Path Computation Element (PCE) to support inter-domain P2MP path computation. This document is not intended to replace the intra-domain P2MP path computation approach supported by [RFC6006], and will not impact existing PCE procedures and operations. 1.3. Requirements Language 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 [RFC 2119]. 2. Terminology Zhao, et al. July 14, 2013 [Page 3] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 Terminology used in this document is consistent with the related MPLS/GMPLS and PCE documents [RFC4461], [RFC4655], [RFC4875], [RFC5376], [RFC5440], [RFC5441], [RFC5671] and [RFC5862]. ABR: Area Border Router. Router used to connect two IGP domains (areas in OSPF or levels in IS-IS). ASBR: Autonomous System Border Router. Router used to connect together ASes of the same or different Service Providers via one or more Inter-AS links. Boundary Node (BN): is either an ABR in the context of inter-area Traffic Engineering or an ASBR in the context of inter-AS Traffic Engineering. Core Tree: a P2MP tree where the root is the ingress LSR, and the leaf nodes are the entry BNs of the leaf domains. Domain: a collection of network elements within a common sphere of address management or path computational responsibility such as an IGP area or an Autonomous System (AS). Entry BN of domain(n): a BN connecting domain(n-1) to domain(n) along a determined sequence of domains. Exit BN of domain(n): a BN connecting domain(n) to domain(n+1) along a determined sequence of domains. Leaf Domain: a domain with one or more leaf nodes. OF: Objective Function. a set of one or more optimization criterion (criteria) used for the computation of paths either for single or for synchronized requests (e.g. path cost minimization), or the synchronized computation of a set of paths (e.g. aggregate bandwidth consumption minimization, etc.). See [RFC4655] and [RFC5541]. Path Tree: a set of LSRs and TE links that comprise the path of a P2MP TE LSP from the ingress LSR to all egress LSRs. Path Domain Sequence: the known sequence of domains for a path between root and leaf. Path Domain Tree: the tree formed by the domains that the P2MP path crosses, where the source (ingress) domain is the root domain. PCE(i): a PCE that performs path computations for domain(i). Root Domain: the domain that includes the ingress (root) LSR. Zhao, et al. July 14, 2013 [Page 4] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 Sub-tree: used to minimize packet duplication when P2P TE sub-LSPs traverse common links. Transit/branch Domain: a domain that has an upstream and one or more downstream neighbor domain. VSPT: Virtual Shortest Path Tree [RFC5441]. 3. Problem Statement The Path Computation Element (PCE) defined in [RFC4655] is an entity that is capable of computing a network path or route based on a network graph, and applying computational constraints. A Path Computation Client (PCC) may make requests to a PCE for paths to be computed. [RFC4875] describes how to set up P2MP TE LSPs for use in MPLS and GMPLS-controlled networks. The PCE is identified as a suitable application for the computation of paths for P2MP TE LSPs [RFC5671]. [RFC5441] specifies a procedure relying on the use of multiple PCEs to compute (P2P) inter-domain constrained shortest paths across a predetermined sequence of domains, using a Backward Recursive Path Computation (BRPC) technique. The technique can be combined with the use of path keys [RFC5520] to preserve confidentiality across domains, which is sometimes required when domains are managed by different Service Providers. The PCE communication Protocol (PCEP) [RFC5440] is extended for point-to-multipoint(P2MP) path computation requests in [RFC6006]. However, [RFC6006] does not provide the necessary mechanisms and procedures to request the computation of inter-domain P2MP TE LSPs. As discussed in [RFC4461], a P2MP tree is a graphical representation of all TE links that are committed for a particular P2MP TE LSP. In other words, a P2MP tree is a representation of the corresponding P2MP tunnel on the TE network topology. A sub-tree is used to minimize packet duplication when P2P TE sub-LSPs traverse common links. As described in [RFC5671] the computation of a P2MP tree requires three major pieces of information. The first is the path from the ingress LSR of a P2MP TE LSP to each of the egress LSRs, the second is the traffic engineering related parameters, and the third is the branch capability information. Generally, an inter-domain P2MP tree (i.e., a P2MP tree with source and at least one destination residing in different domains) is particularly difficult to compute even for a distributed PCE architecture. For instance, while the BRPC may be well-suited for Zhao, et al. July 14, 2013 [Page 5] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 P2P paths, P2MP path computation involves multiple branching path segments from the source to the multiple destinations. As such, inter-domain P2MP path computation may result in a plurality of per-domain path options that may be difficult to coordinate efficiently and effectively between domains. That is, when one or more domains have multiple ingress and/or egress boundary nodes, there is currently no known technique for one domain to determine which boundary node of another domain will be utilized for the inter-domain P2MP tree, and no way to limit the computation of the P2MP tree to those utilized boundary nodes. A trivial solution to the computation of inter-domain P2MP tree would be to compute shortest inter-domain P2P paths from source to each destination and then combine them to generate an inter-domain, shortest-path-to-destination P2MP tree. This solution, however, cannot be used to trade cost to destination for overall tree cost (i.e., it cannot produce a Minimum Cost Tree (MCT)) and in the context of inter- domain P2MP TE LSPs it cannot be used to reduce the number of domain boundary nodes that are transited. Computing P2P TE LSPs individually is not an acceptable solution for computing a P2MP tree. Even per domain path computation [RFC5152] can be used to compute P2P multi-domain paths, but it does not guarantee to find the optimal path which crosses multiple domains. Furthermore, constructing a P2MP tree from individual source to leaf P2P TE LSPs does not guarantee to produce a Minimum Cost Tree (MCT). This approach may also be considered to have scaling issues during LSP setup. That is, the LSP to each leaf is signaled separately, and each boundary node must perform path computation for each leaf. P2MP Minimum Cost Tree (MCT), i.e. a computation which guarantees the least cost resulting tree, is an NP-complete problem. Moreover, adding and/or removing a single destination to/from the tree may result in an entirely different tree. In this case, frequent MCT path computation requests may prove computationally intensive, and the resulting frequent tunnel reconfiguration may even cause network destabilization. This document presents a solution, procedures and extensions to PCEP to support P2MP inter-domain path computation. 4. Assumptions Within this document we make the following assumptions: o Due to deployment and commercial limitations (e.g., inter-AS peering agreements), the path domain tree will be known in advance; Zhao, et al. July 14, 2013 [Page 6] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 o Each PCE knows about any leaf LSRs in the domain it serves; Additional assumptions are documented in [RFC5441] and will not be repeated here. 5. Requirements This section summarizes the requirements specific to computing inter- domain P2MP paths. In these requirements we note that the actual computation time taken by any PCE implementation is outside the scope of this document, but we observe that reducing the complexity of the required computations has a beneficial effect on the computation time regardless of implementation. Additionally, reducing the number of message exchanges and the amount of information exchanged will reduce the overall computation time for the entire P2MP tree. We refer to the "complexity of the computation" as the impact on these aspects of path computation time as various parameters of the topology and the P2MP TE LSP are changed. It is also important that the solution preserves confidentiality across domains, which is required when domains are managed by different Service Providers. Other than the requirements specified in [RFC5862], a number of requirements specific to P2MP are detailed below: 1. The computed P2MP TE LSP SHOULD be optimal when only considering the paths among the BNs. 2. Grafting and pruning of multicast destinations in a domain SHOULD have no impact on other domains and on the paths among BNs. 3. The complexity of the computation for each sub-tree within each domain SHOULD be dependent only on the topology of the domain and it SHOULD be independent of the domain sequence. 4. The number of PCReq and PCReq messages SHOULD be independent of the number of multicast destinations in each domain. 5. It SHOULD be possible to specify the domain entry and exit nodes. 6. Specifying which nodes are be used as branch nodes SHOULD be supported. 7. Reoptimization of existing sub-trees SHOULD be supported. 8. It SHOULD be possible to compute diverse P2MP paths from existing P2MP paths. Zhao, et al. July 14, 2013 [Page 7] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 6. Objective Functions and Constraints For the computation of a single or a set of P2MP TE LSPs, a request to meet specific optimization criteria, called an Objective Function (OF), may be used. Using an OF to select the "best" candidate path, include: o The sub-tree within each domain SHOULD be optimized using minimum cost tree [RFC5862], or shortest path tree [RFC5862]. In addition to the OFs, the following constraint optimization may also be beneficial for P2MP path computation: 1. The core tree SHOULD be optimal. 2. It SHOULD be possible to limit the number of entry points to a domain. 3. It SHOULD be possible to force the branches for all leaves within a domain to be in that domain. 4. It SHOULD be possible to combine the aforementioned OFs and constraints for P2MP path computation. The algorithms used to compute optimal paths using a combination of OFs and multiple constraints is out of scope of this document. 7. P2MP Path Computation Procedures The following sections describe the core tree-based procedures to satisfy the requirements specified in the previous section. A core tree-based solution provides an optimal inter-domain P2MP TE LSP. 7.1. Core Trees A core tree is defined as a tree that satisfies the following conditions: o The root of the core tree is the ingress LSR in the root domain; o The leaves of the core tree are the entry nodes in the leaf domains. To support confidentiality these nodes and links may be hidden using the path-key mechanism [RFC5520], but they MUST be computed and be a part of core-tree. For example, consider the Domain Tree in Figure 1 below, representing a domain tree of 6 domains, and part of the resulting core tree which satisfies the aforementioned conditions. Zhao, et al. July 14, 2013 [Page 8] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 +----------------+ | |Domain D1 | R | | | | A | | | +-B------------C-+ / \ / \ / \ Domain D2 / \ Domain D3 +-------------D--+ +-----E----------+ | | | | | F | | | | G | | H | | | | | | | | | +-I--------------+ +-J------------K-+ / / \ / / \ / / \ / / \ / / \ / / \ / Domain D4 Domain D5 / Domain D6 \ +-L--------------+ +------P---------+ +-----------T----+ | | | | | | | | | Q | | U | | M O | | S | | | | | | | | V | | N | | R | | | +----------------+ +----------------+ +----------------+ Figure 1: Domain Tree Example Zhao, et al. July 14, 2013 [Page 9] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 (R) | (A) / \ / \ (B) (C) / \ / \ (D) (E) / | / | (G) (H) / / \ / / \ (I) (J) (K) / / \ / / \ (L) (P) (T) Figure 2: Core Tree A core tree is computed such that root of the tree is R and the leaf node are the entry nodes of the destination domains (L, P and T). Path-key mechanism can be used to hide the internal nodes and links in the final core tree. 7.2. Core Tree Computation Procedures The algorithms to compute the optimal large core tree are outside scope of this document. The following extended BRPC-based procedure can be used to compute the core tree. A BRPC-based core tree path computation procedure is described below: 1. Using the BRPC procedures to compute the VSPT(i) for each leaf BN(i), i=1 to n, where n is the total number of entry nodes for all the leaf domains. In each VSPT(i), there are a number of P(i) paths. 2. When the root PCE has computed all the VSPT(i), i=1 to n, take one path from each VSPT and form all possible sets of paths, we call them PathSet(j), j=1 to M, where M=P(1)xP(2)...xP(n); 3. For each PathSet(j), there are n S2L (Source to Leaf BN) paths and form these n paths into a core tree(j); 4. There will be M number of core trees computed from step3. Apply the OF to each of these M core trees and find the optimal Core Tree. Zhao, et al. July 14, 2013 [Page 10] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 Note that, since point to point BRPC procedure is used to compute VSPT, the path request and response messages as per [RFC5440] are used. Also note that the application of BRPC in the aforementioned procedure differs from the typical one since paths returned from a downstream PCE are not necessarily pruned from the solution set by intermediate PCEs. The reason for this is that if the PCE in a downstream domain does the pruning and returns the single optimal sub-path to the upstream PCE, BRPC insures that the ingress PCE will get all the best optimal sub-paths for each LN (Leaf Boundary Nodes), but the combination of these single optimal sub-paths into a P2MP tree is not necessarily optimal even if each S2L (Source-to-Leaf) sub-path is optimal. Without trimming, the ingress PCE will obtain all the possible S2L sub-paths set for LN. The PCE will then, by looking through all the combinations and taking one sub-path from each set to build one P2MP tree, can find the optimal tree. A PCE MAY add equal cost paths within the domain while constructing an extended VSPT. This will provide the ingress PCE more candidate paths for an optimal P2MP tree. The proposed method may present a scalability problem for the dynamic computation of the core tree (by iterative checking of all combinations of the solution space), specially with dense/meshed domains. Considering a domain sequence D1, D2, D3, D4, where the Leaf Boundary Node is at domain D4, PCE(4) will return 1 path. PCE(3) will return N paths, where N is E(3) x X(3), where E(k) x X(k) denotes the number of entry nodes times the number of exit nodes for that domain. PCE(2) will return M paths, where M = E(2) x X(2) x N = E(2) x X(2) x E(3) x X(3) x 1, etc. Generally speaking the number of potential paths at the ingress PCE Q = \prod E(k) x X(k). Consequently, it is expected that the Core Path will be typically computed offline, without precluding the use of dynamic, online mechanisms such as the one presented here, in which case it SHOULD be possible to configure transit PCEs to control the number of paths sent upstream during BRPC (trading trimming for optimality at the point of trimming and downwards). 7.3. Sub-tree Computation Procedures Once the core tree is built, the grafting of all the leaf nodes from each domain to the core tree can be achieved by a number of algorithms. One algorithm for doing this phase is that the root PCE will send the request with C bit set (as defined in section 7.4.1 of this document) for the path computation to the destination(s) Zhao, et al. July 14, 2013 [Page 11] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 directly to the PCE where the destination(s) belong(s) along with the core tree computed from section 7.1. This approach requires that the root PCE manage a potentially large number of adjacencies (either in persistent or non-persistent mode), including PCEP adjacencies to PCEs that are not within neighbor domains. A first alternative would involve establishing PCEP adjacencies that correspond to the PCE domain tree. This would require that branch PCEs forward requests and responses from the root PCE towards the leaf PCEs and vice-versa. Note that the P2MP path request and response format is as per [RFC6006], where Record Route Object (RRO) are used to carry the core-tree paths in the P2MP grafting request. The algorithms to compute the optimal large sub-tree are outside scope of this document. 7.4. PCEP Protocol Extensions 7.4.1. The Extension of RP Object This experiment will be carried out by extending the RP (Request Parameters) object (defined in [RFC5440]) used in Path Request and Reply messages. The extended format of the RP object body to include the C bit is as follows: The C bit is added in the flag bits field of the RP object to signal the receiver of the message that the request/reply is for inter- domain P2MP core tree or not. The following flag is added in this draft: C bit ( P2MP Core Tree bit - 1 bit): 0: This indicates that this is normal PCReq/PCRrep for P2MP. 1: This indicates that this is PCReq or PCRep message for inter- domain core tree P2MP. When the C bit is set, then the request message MUST contain the core tree passed along with the destinations to be grafted to the tree. 7.4.2. Domain and PCE Sequence The procedure as described in this document requires the domain-tree Zhao, et al. July 14, 2013 [Page 12] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 to be known in advance. This information may be provided dynamically as documented in the Hierarchical PCE (H-PCE) [RFC6805] framework, or obtained through the IGP/BGP routing information. [DOMAIN-SEQ] describes the representation of domain in P2MP scenarios. The use of PCE sequence rather than domain-sequence, is based on deployment and implementation preference. 7.5. Using H-PCE for Scalability The ingress/root PCE is responsible for the grafting of sub-trees into the multi-domain tree. Therefore, the ingress/root PCE will receive all computed sub-trees from all the involved domains. This will require the ingress/root PCE to have a PCEP session with all PCEs providing sub-trees. This may cause an excessive number of sessions or added complexity in implementations. The use of the H-PCE framework [RFC6805] may be used to establish a dedicated PCE with the capability (memory and CPU) and knowledge to maintain the necessary PCEP sessions. The parent PCE would be responsible to request intra-domain sub-trees to the PCEs, combine them and return the overall P2MP tree. 7.6. Parallelism In order to minimize latency in path computation in multi-domain networks, intra-domain path segments and intra-domain sub-trees SHOULD be computed in parallel when possible. The proposed procedures in this draft present opportunities for parallelism: 1. The BRPC procedure for each leaf node can be launched in parallel by the ingress/root PCE if the dynamic computation of the Core Tree is enabled. 2. Intra-domain P2MP paths can also be computed in parallel by the PCEs once the entry and exit nodes within a domain are known One of the potential issues of parallelism is that the ingress PCE would require a potentially high number of PCEP adjacencies to "remote" PCEs and that may not be desirable, but a given PCE would only receive requests for the destinations that are in its domain (+ the core nodes), without PCEs forwarding requests. 8. Protection It is envisaged that protection may be required when deploying and using inter-domain P2MP TE LSPs. The procedures and mechanisms defined in this document do not prohibit the use of existing and Zhao, et al. July 14, 2013 [Page 13] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 proposed types of protection, including: end-to-end protection [RFC4875] and domain protection schemes. Segment or facility (link and node) protection is problematic in inter-domain environment due to the limit of Fast-reroute (FRR) [RFC4875] requiring knowledge of its next-hop across domain boundaries whilst maintaining domain confidentiality. Although the FRR protection might be implemented if next-hop information was known in advance. 8.1. End-to-end Protection An end-to-end protection (for nodes and links) principle can be applied for computing backup P2MP TE LSPs. During computation of the core-tree and sub-trees, may also be taken into consideration. A PCE may compute the primary and backup P2MP TE LSP together or sequentially. 8.2. Domain Protection In this protection scheme, backup P2MP Tree can be computed which excludes the transit/branch domain completely. A backup domain path tree is needed with the same source domain and destinations domains and a new set of transit domains. The backup path tree can be applied to the above procedure to obtain the backup P2MP TE LSP with disjoint transit domains. 9. Manageability Considerations [RFC5862] describes various manageability requirements in support of P2MP path computation when applying PCEP. This section describes how manageability requirements mentioned in [RFC5862] are supported in the context of PCEP extensions specified in this document. Note that [RFC5440] describes various manageability considerations in PCEP, and most of manageability requirements mentioned in [RFC6006] are already covered there. 9.1. Control of Function and Policy In addition to PCE configuration parameters listed in [RFC5440], the following additional parameters might be required: o The ability to enable or disable single domain P2MP path computations on the PCE. o The ability to enable or disable multi-domain P2MP path computations on the PCE. Zhao, et al. July 14, 2013 [Page 14] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 o The PCE may be configured to enable or disable the advertisement of its single domain and multi-domain P2MP path computation capability. 9.2. Information and Data Models A number of MIB objects have been defined for general PCEP control and monitoring of P2P computations in [PCEP-MIB]. [RFC5862] specifies that MIB objects will be required to support the control and monitoring of the protocol extensions defined in this document. [PCEP-P2MP-MIB] describes managed objects for modeling of PCEP communications between a PCC and PCE, and PCE to PCE, P2MP path computation requests and responses. 9.3. Liveness Detection and Monitoring No changes are necessary to the liveness detection and monitoring requirements as already embodied in [RFC4657]. It should be noted that multi-domain P2MP computations are likely to take longer than P2P computations, and single domain P2MP computations. The liveness detection and monitoring features of the PCEP SHOULD take this into account. 9.4. Verifying Correct Operation There are no additional requirements beyond those expressed in [RFC4657] for verifying the correct operation of the PCEP. Note that verification of the correct operation of the PCE and its algorithms is out of scope for the protocol requirements, but a PCC MAY send the same request to more than one PCE and compare the results. 9.5. Requirements on Other Protocols and Functional Components A PCE operates on a topology graph that may be built using information distributed by TE extensions to the routing protocol operating within the network. In order that the PCE can select a suitable path for the signaling protocol to use to install the P2MP TE LSP, the topology graph MUST include information about the P2MP signaling and branching capabilities of each LSR in the network. Mechanisms for the knowledge of other domains, the discovery of corresponding PCEs and their capabilities should be provided and that this information MAY be collected by other mechanisms. Whatever means is used to collect the information to build the topology graph, the graph MUST include the requisite information. If the TE extensions to the routing protocol are used, these SHOULD be as described in [RFC5073]. Zhao, et al. July 14, 2013 [Page 15] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 9.6. Impact on Network Operation The use of a PCE to compute P2MP paths is not expected to have significant impact on network operations. However, it should be noted that the introduction of P2MP support to a PCE that already provides P2P path computation might change the loading of the PCE significantly, and that might have an impact on the network behavior, especially during recovery periods immediately after a network failure. The dynamic computation of core trees might also have an impact on the load of the involved PCEs as well as path computation times. 9.7. Policy Control [RFC5394] provides additional details on policy within the PCE architecture and also provides context for the support of PCE Policy. They are also applicable to Inter-domain P2MP Path computation via the core tree mechanism. 10. Security Considerations As described in [RFC5862], P2MP path computation requests are more CPU-intensive and also utilize more link bandwidth. In the event of an unauthorized P2MP path computation request, or a denial of service attack, the subsequent PCEP requests and processing may be disruptive to the network. Consequently, it is important that implementations conform to the relevant security requirements of [RFC5440] that specifically help to minimize or negate unauthorized P2MP path computation requests and denial of service attacks. These mechanisms include: o Securing the PCEP session requests and responses using TCP security techniques (Section 10.2 of [RFC5440]). o Authenticating the PCEP requests and responses to ensure the message is intact and sent from an authorized node (Section 10.3 of [RFC5440]). o Providing policy control by explicitly defining which PCCs, via IP access-lists, are allowed to send P2MP path requests to the PCE (Section 10.6 of [RFC5440]). PCEP operates over TCP, so it is also important to secure the PCE and PCC against TCP denial of service attacks. Section 10.7.1 of [RFC5440] outlines a number of mechanisms for minimizing the risk of TCP-based denial of service attacks against PCEs and PCCs. Zhao, et al. July 14, 2013 [Page 16] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 PCEP implementations SHOULD also consider the additional security provided by the TCP Authentication Option (TCP-AO) [RFC 5925]. 11. IANA Considerations Due to the experimental status of this document. No IANA considerations have been requested. 12. Acknowledgements The authors would like to thank Adrian Farrel, Dan Tappan, Olufemi Komolafe, Oscar Gonzalez de Dios and Julien Meuric for their valuable comments on this document. 13. References 13.1. Normative References [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC5440, March 2009. [RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Procedure to Compute Shortest Constrained Inter- Domain Traffic Engineering Label Switched Paths", RFC5441, April 2009. [RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)", RFC5541, June 2009. [RFC6006] Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z., and J. Meuric, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Point-to-Multipoint Traffic Engineering Label Switched Paths", RFC6006, September 2010. 13.2. Informative References [RFC4461] Yasukawa, S., "Signaling Requirements for Point-to- Multipoint Traffic-Engineered MPLS Label Switched Paths (LSPs)", RFC4461, April 2006. Zhao, et al. July 14, 2013 [Page 17] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC4655, August 2006. [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC4657, September 2006. [RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa, "Extensions to Resource Reservation Protocol - Traffic Engineering (RSVP-TE) for Point-to- Multipoint TE Label Switched Paths (LSPs)", RFC4875, May 2007. [RFC5073] Vasseur, J. and J. Le Roux, "IGP Routing Protocol Extensions for Discovery of Traffic Engineering Node Capabilities", RFC5073, December 2007. [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)", RFC5152, February 2008. [RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)", RFC5376, November 2008. [RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash, "Policy-Enabled Path Computation Framework", RFC5394, December 2008. [RFC5520] Bradford, R., Vasseur, JP., and A. Farrel, "Preserving Topology Confidentiality in Inter-Domain Path Computation Using a Path-Key-Based Mechanism", RFC5520, April 2009. [RFC5671] Yasukawa, S. and A. Farrel, "Applicability of the Path Computation Element (PCE) to Point-to- Multipoint (P2MP) MPLS and GMPLS Traffic Engineering (TE)", RFC5671, October 2009. [RFC5862] Yasukawa, S. and A. Farrel, "Path Computation Clients (PCC) - Path Computation Element (PCE) Requirements for Point-to-Multipoint MPLS-TE", RFC5862, June 2010. [RFC 5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, June 2010. Zhao, et al. July 14, 2013 [Page 18] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 [RFC6805] King, D. and A. Farrel, "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS and GMPLS", RFC6805, November 2012. [PCEP-MIB] Koushik, K., Stephan, E., Zhao, Q., King, D., and J. Hardwick, "PCE communication protocol (PCEP) Management Information Base (Work in Progress)", July 2012. [PCEP-P2MP-MIB] Zhao, Q., Dhody, D., Palle, U., and D. King, "Management Information Base for the PCE Communications Protocol (PCEP) When Requesting Point-to-Multipoint Services (Work in Progress)", Aug 2012. [DOMAIN-SEQ] Dhody, D., Palle, U., and R. Casellas, "Standard Representation Of Domain Sequence (Work in Progress)", Feb 2013. 14. Contributor Addresses Siva Sivabalan Cisco Systems 2000 Innovation Drive Kanata, Ontario K2K 3E8 CANADA EMail: email@example.com Tarek Saad Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario K2K 3E8 CANADA EMail: firstname.lastname@example.org 15. Authors' Addresses Quintin Zhao Huawei Technology 125 Nagog Technology Park Acton, MA 01719 US EMail: email@example.com Zhao, et al. July 14, 2013 [Page 19] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014 Dhruv Dhody Huawei Technology Leela Palace Bangalore, Karnataka 560008 INDIA EMail: firstname.lastname@example.org Zafar Ali Cisco Systems 2000 Innovation Drive Kanata, Ontario K2K 3E8 CANADA EMail: email@example.com Daniel King Old Dog Consulting UK EMail: firstname.lastname@example.org Ramon Casellas CTTC - Centre Tecnologic de Telecomunicacions de Catalunya Av. Carl Friedrich Gauss n7 Castelldefels, Barcelona 08860 SPAIN EMail: email@example.com Zhao, et al. July 14, 2013 [Page 20] Internet-Draft PCEP P2MP Inter-Domain Procedures January 2014