PCE Working Group Q. Zhao Internet-Draft D. Dhody Intended status: Experimental Huawei Technology Expires: December 17, 2014 D. King Old Dog Consulting Z. Ali Cisco Systems R. Casellas CTTC June 17, 2014 PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths draft-ietf-pce-pcep-inter-domain-p2mp-procedures-08 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 December 17, 2014. Copyright Notice Zhao, et al. Expires December 17, 2014 [Page 1] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . .2 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . .2 1.2. Requirements Language . . . . . . . . . . . . . . . . . .2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . .2 3. Examination of Existing Mechanisms . . . . . . . . . . . . .3 4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . .5 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . .5 6. Objective Functions and Constraints. . . . . . . . . . . . . .7 7. P2MP Path Computation Procedures . . . . . . . . . . . . . . .8 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . .8 7.2. Core-Trees . . . . . . . . . . . . . . . . . . . . . . . .9 7.3. Optimal Core-Tree Computation Procedure. . . . . . . . . .12 7.4. Sub-tree Computation Procedures . . . . . . . . . . . . .13 7.5. PCEP Protocol Extensions . . . . . . . . . . . . . . . . .13 7.5.1. The Extension of RP Object . . . . . . . . . . . . . .13 7.5.2. Domain and PCE Sequence . . . . . . . . . . . . . . .14 7.6. Relationship with Hierarchical PCE . . . . . . . . . . . .14 7.7. Parallelism . . . . . . . . . . . . . . . . . . . . . . .15 8. Protection . . . . . . . . . . . . . . . . . . . . . . . . . .15 8.1. End-to-end Protection . . . . . . . . . . . . . . . . . .15 8.2. Domain Protection . . . . . . . . . . . . . . . . . . . .15 9. Manageability Considerations . . . . . . . . . . . . . . . . .16 9.1. Control of Function and Policy . . . . . . . . . . . . . .16 9.2. Information and Data Models . . . . . . . . . . . . . . .16 9.3. Liveness Detection and Monitoring . . . . . . . . . . . .16 9.4. Verifying Correct Operation . . . . . . . . . . . . . . .16 9.5. Requirements on Other Protocols and Functional Components.17 9.6. Impact on Network Operation . . . . . . . . . . . . . . .17 9.7. Policy Control . . . . . . . . . . . . . . . . . . . . . .17 10. Security Considerations . . . . . . . . . . . . . . . . . . .17 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .18 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .19 13. References . . . . . . . . . . . . . . . . . . . . . . . . . .19 13.1. Normative References . . . . . . . . . . . . . . . . . . .19 Zhao, et al. Expires December 17, 2014 [Page 2] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 13.2. Informative References . . . . . . . . . . . . . . . . . .19 14. Contributors' Addresses . . . . . . . . . . . . . . . . . . .21 15. Authors' Addresses . . . . . . . . . . . . . . . . . . . . .21 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 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. When results of implementation and deployment are available, this document will be updated and refined, and then moved from Experimental status to Standards Track. 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 usage of the PCE to support inter-domain P2MP path computation. This document is not intended to replace the intra-domain P2MP path computation approach defined 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 [RFC2119]. 2. Terminology Zhao, et al. Expires December 17, 2014 [Page 3] Internet-Draft PCEP P2MP Inter-Domain Procedures June 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]. The additional terms Core-Tree, Leaf Domain, Path Tree, Path Domain Sequence, Path Domain Tree, Root Domain, Sub-Tree and Transit/branch Domain are further defined below. Core-Tree: a P2MP tree where the root is the ingress Label Switching Router (LSR), and the leaf nodes are the entry BNs of the leaf domains. Entry BN of domain(n): a Boundary Node (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. H-PCE: Hierarchical PCE (as per [RFC6805]). Leaf Domain: a domain with one or more leaf nodes. 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 (the leaf nodes). Path Domain Sequence: the known sequence of domains for a path between the root domain and a leaf domain. 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. Sub-tree: a P2MP tree where the root is the selected entry BN of the leaf domain and the leaf nodes are the destinations (leaves) in that domain. The sub-trees are grafted to the core-tree. Transit/branch Domain: a domain that has an upstream and one or more downstream neighbor domain. 3. Examination of Existing Mechanisms 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 Zhao, et al. Expires December 17, 2014 [Page 3] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 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 Point to Point (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. PCEP [RFC5440] was extended for point-to-multipoint (P2MP) path computation requests in [RFC6006]. As discussed in [RFC4461], a P2MP tree is the ordered set of LSRs and TE links that comprise the path of a P2MP TE LSP from its ingress LSR to all of its egress LSRs. A P2MP LSP is set up with TE constraints and allows efficient packet or data replication at various branching points in the network. As per [RFC5671] branch point selection is fundamental to the determination of the paths for a P2MP TE LSP. Not only is this selection constrained by the network topology and available network resources, but it is determined by the objective functions (OF) that may be applied to path computation. 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 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 (i.e., when the domains are multiply inter-connected), existing techniques may be convoluted when used 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 Zhao, et al. Expires December 17, 2014 [Page 4] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 (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 does not guarantee the generation of an optimal P2MP tree for every definition of "optimal" in every topology. Per Domain path computation [RFC5152] may be used to compute P2MP multi-domain paths, but may encounter the issues previously described. Furthermore, 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 needs to perform path computation for each leaf. P2MP Minimum Cost Tree (MCT), i.e. a computation which guarantees the least cost resulting tree, typically 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 (Autonomous System) peering agreements), the path domain tree will be known in advance; o Each PCE knows about any leaf LSRs in the domain it serves; Additional assumptions are documented in [RFC5441] and are not 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 Zhao, et al. Expires December 17, 2014 [Page 5] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 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 can preserve confidentiality across domains, which is required when domains are managed by different Service Providers via Path-Key mechanism [RFC5520]. Other than the requirements specified in [RFC5862], a number of requirements specific to inter-domain P2MP are detailed below: 1. 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. 2. The number of PCReq (Path Computation Request) and PCRep (Path Computation Reply) messages SHOULD be independent of the number of multicast destinations in each domain. 3. It SHOULD be possible to specify the domain entry and exit nodes in the PCReq. 4. Specifying which nodes are be used as branch nodes SHOULD be supported in the PCReq. 5. Reoptimization of existing sub-trees SHOULD be supported. 6. It SHOULD be possible to compute diverse P2MP paths from existing P2MP paths. 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 constraints MAY also be beneficial for inter-domain P2MP path computation: 1. The computed P2MP "core-tree" SHOULD be optimal when only considering the paths to the leaf domain entry BNs. 2. Grafting and pruning of multicast destinations (sub-tree) within a leaf domain SHOULD ensure minimal impact on other domains Zhao, et al. Expires December 17, 2014 [Page 7] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 and on the core-tree. 3. It SHOULD be possible to choose to optimize the core-tree. 4. It SHOULD be possible to choose optimize the entire tree (P2MP LSP). 5. It SHOULD be possible to combine the aforementioned OFs and constraints for P2MP path computation. When implementing and operating P2MP LSPs, following needs to be taken into consideration: o The complexity of computation. o The optimality of the tree (core-tree as well as full P2MP LSP tree). o The stability of the core-tree. The solution SHOULD allow these trade-offs to be made at computation time. 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 7.1. General A P2MP path computation can be broken down into two steps of core-tree computation and grafting of sub-trees. Breaking the procedure into these specific steps has the following impact: o The core-tree and sub-tree are smaller in comparison to the full P2MP Tree and are thus easier to compute. o An implementation MAY choose to keep the core-tree fairly static or computed offline (trade-off with optimality). o Adding/Pruning of leaves which require changes to sub-tree in leaf- domain only. o The PCEP message size is smaller in comparison. Allowing the core-tree based solution to provide an optimal inter-domain P2MP TE LSP. Zhao, et al. Expires December 17, 2014 [Page 8] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 The following sub-sections describe the core-tree based mechanism, including procedures and PCEP extensions, that satisfy the requirements and objectives specified in Section 5 and Section 6 of this document. 7.2. 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 boundary 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. Expires December 17, 2014 [Page 9] Internet-Draft PCEP P2MP Inter-Domain Procedures June 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-------------W+ +------P---------+ +-----------T----+ | | | | | | | | | Q | | U | | M O | | S | | | | | | | | V | | N | | R | | | +----------------+ +----------------+ +----------------+ Figure 1: Domain Tree Example Zhao, et al. Expires December 17, 2014 [Page 10] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 (R) | (A) / \ / \ (B) (C) / \ / \ (D) (E) / | / | (G) (H) / / \ / / \ (I) (J) (K) / \ / \ / \ / \ (L) (W) (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, W, P and T). Path-key mechanism can be used to hide the internal nodes and links (node G and H are hidden via Path-Key PK1 and PK2 respectively) in the final core-tree as shown below for domain D2 and D3. (R) | (A) / \ / \ (B) (C) / \ / \ (D) (E) / | / | |PK1| |PK2| / / \ / / \ (I) (J) (K) / \ / \ / \ / \ (L) (W) (P) (T) Figure 3: Core-Tree with Path-Key Zhao, et al. Expires December 17, 2014 [Page 11] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 7.3. Optimal Core-Tree Computation Procedure Applying the core-tree procedure to large groups of domains, such as the Internet, is not considered feasible or desirable, and is out of scope for this document. The following extended BRPC-based procedure can be used to compute the core-tree. Note that a root PCE MAY further use its own enhanced optimization techniques in future 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) (Virtual Shortest Path Tree) 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 core-trees computed from step 3. An optimal core-tree is selected based on the OF and constraints. Note that, since point to point BRPC procedure is used to compute VSPT, the path request and response message format defined in [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 (extended VSPT) 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, the combination of these single optimal sub-paths into a core-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 the entry boundary nodes of the leaf domain. The PCE will then, by looking through all the combinations and taking one sub-path from each set to build one tree, can select the optimal core-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 core-tree. Zhao, et al. Expires December 17, 2014 [Page 12] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 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-tree 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). 7.4. 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) directly to the PCE where the destination(s) belong(s) along with the core-tree computed from section 7.2. 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. An 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. 7.5. PCEP Protocol Extensions 7.5.1. The Extension of RP Object Zhao, et al. Expires December 17, 2014 [Page 13] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 This experiment will be carried out by extending the RP (Request Parameters) object (defined in [RFC5440]) used in PCEP requests and responses. 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: Bit Number Name Flag TBA Core-tree computation (C-bit) C bit (Core-Tree bit - 1 bit): 0: This indicates that this is not for an inter-domain P2MP core-tree. 1: This indicates that this is a PCEP request or a response for the computation of a inter-domain core-tree or for the grafting of a sub-tree to a inter-domain core-tree. 7.5.2. Domain and PCE Sequence The procedure described in this document requires the domain-tree to be known in advance. This information MAY be either administratively predetermined or dynamically discovered by some means such as Hierarchical PCE (H-PCE) [RFC6805] framework, or derived through the IGP/BGP routing information. Examples of ways to encode the domain path tree include [RFC5886] using PCE-ID Object and [DOMAIN-SEQ]. 7.6. Using H-PCE for Scalability The ingress/root PCE is responsible for the core-tree computation as well as grafting of sub-trees into the multi-domain tree. Therefore, the ingress/root PCE will receive all computed path segments from all the involved domains. When the ingress/root PCE chooses to have a PCEP session with all involved PCEs, 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 path computation request to the Zhao, et al. Expires December 17, 2014 [Page 14] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 PCEs, combine them and return the overall P2MP tree. 7.7. Parallelism In order to minimize latency in path computation in multi-domain networks, intra-domain path segments and intra-domain sub-trees can be computed in parallel when possible. The proposed procedures in this draft present opportunities for parallelism: 1. The BRPC procedure for each leaf boundary node can be launched in parallel by the ingress/root PCE for dynamic computation of core-tree. 2. The grafting of sub-trees can be triggered in parallel once the core-tree is computed. One of the potential issues of parallelism is that the ingress PCE would require a potentially high number of PCEP adjacencies to "remote" PCEs at the same time and that may not be desirable. 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 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 Zhao, et al. Expires December 17, 2014 [Page 15] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 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] and [RFC6006], the following additional parameters might be required: o The ability to enable or disable multi-domain P2MP path computations on the PCE. o The PCE may be configured to enable or disable the advertisement of its 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 Zhao, et al. Expires December 17, 2014 [Page 16] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 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]. 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. It should be noted that pre-computing and maintaining domain-trees might be a considerable administration effort on the operator. 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 Zhao, et al. Expires December 17, 2014 [Page 17] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 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. PCEP implementations SHOULD also consider the additional security provided by the TCP Authentication Option (TCP-AO) [RFC5925]. Finally, any multi-domain operation necessarily involves the exchange of information across domain boundaries. This may represent a significant security and confidentiality risk especially when the domains are controlled by different commercial entities. PCEP allows individual PCEs to maintain confidentiality of their domain path information by using path-keys [RFC5520] and would allow for securing of domain path information when performing core-tree based path computations. 11. IANA Considerations IANA maintains the "Path Computation Element Protocol (PCEP) Numbers" registry with the "RP Object Flag Field" sub-registry. IANA is requested to allocate a new bit from this registry as follows: Bit Description Reference Zhao, et al. Expires December 17, 2014 [Page 18] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 TBA Core-tree computation (C-bit) [This.I-D] 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 [RFC2119] 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)", RFC 5440, 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", RFC 5441, April 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", RFC 6006, September 2010. 13.2. Informative References [RFC4461] Yasukawa, S., "Signaling Requirements for Point-to- Multipoint Traffic-Engineered MPLS Label Switched Paths (LSPs)", RFC 4461, April 2006. [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. [RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa, "Extensions to Resource Reservation Protocol - Zhao, et al. Expires December 17, 2014 [Page 19] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 Traffic Engineering (RSVP-TE) for Point-to- Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007. [RFC5073] Vasseur, J. and J. Le Roux, "IGP Routing Protocol Extensions for Discovery of Traffic Engineering Node Capabilities", RFC 5073, 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)", RFC 5152, February 2008. [RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)", RFC 5376, November 2008. [RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash, "Policy-Enabled Path Computation Framework", RFC 5394, December 2008. [RFC5520] Bradford, R., Vasseur, JP., and A. Farrel, "Preserving Topology Confidentiality in Inter-Domain Path Computation Using a Path-Key-Based Mechanism", RFC 5520, 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)", RFC 5671, October 2009. [RFC5862] Yasukawa, S. and A. Farrel, "Path Computation Clients (PCC) - Path Computation Element (PCE) Requirements for Point-to-Multipoint MPLS-TE", RFC 5862, June 2010. [RFC5886] Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A Set of Monitoring Tools for Path Computation Element (PCE)-Based Architecture", RFC 5886, June 2010. [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, June 2010. [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", RFC 6805, November 2012. Zhao, et al. Expires December 17, 2014 [Page 20] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 [PCEP-MIB] Koushik, K., Stephan, E., Zhao, Q., King, D., and J. Hardwick, "PCE communication protocol (PCEP) Management Information Base (Work in Progress)", April 2014. [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)", July 2014. 14. Contributor Addresses Siva Sivabalan Cisco Systems 2000 Innovation Drive Kanata, Ontario K2K 3E8 CANADA EMail: msiva@cisco.com Tarek Saad Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario K2K 3E8 CANADA EMail: tsaad@cisco.com 15. Authors' Addresses Quintin Zhao Huawei Technology 125 Nagog Technology Park Acton, MA 01719 US EMail: quintin.zhao@huawei.com Dhruv Dhody Huawei Technology Leela Palace Bangalore, Karnataka 560008 Zhao, et al. Expires December 17, 2014 [Page 21] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014 INDIA EMail: dhruv.dhody@huawei.com Zafar Ali Cisco Systems 2000 Innovation Drive Kanata, Ontario K2K 3E8 CANADA EMail: zali@cisco.com Daniel King Old Dog Consulting UK EMail: daniel@olddog.co.uk Ramon Casellas CTTC Av. Carl Friedrich Gauss n7 Castelldefels, Barcelona 08860 SPAIN EMail: ramon.casellas@cttc.es Zhao, et al. Expires December 17, 2014 [Page 22] Internet-Draft PCEP P2MP Inter-Domain Procedures June 2014