Internet Engineering Task Force Q. Zhao Internet-Draft Huawei Technology Intended status: Standards Track Z.Ali Created: October 24, 2009 T. Saad Expires: March 24, 2009 Cisco Systems, Inc. D. King Old Dog Consulting PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths draft-zhao-pce-pcep-inter-domain-p2mp-procedures-02.txt Abstract The ability to compute constrained Point-to-multipoint (P2MP) Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE LSPs) across multiple domains has been identified as a key requirement. 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 the procedures and extensions to the PCE communication Protocol (PCEP) to handle requests and responses for the computation of inter-domain paths for P2MP TE LSPs. 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 December 3, 2009. Zhao, et al. [Page 1] Internet-Draft October 2009 Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Zhao, et al. [Page 2] Internet-Draft October 2009 Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Computing a P2MP Tree . . . . . . . . . . . . . . . . . . . 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 6. Objective Functions . . . . . . . . . . . . . . . . . . . . . 7. Protocol Procedures . . . . . . . . . . . . . . . . . . . . . 7.1. Per Domain P2MP Path Computation . . . . . . . . . . . . . 7.2. Extending BRPC for P2MP Computation . . . . . . . . . . . 7.2.1. Definition of X-VSPT(i) . . . . . . . . . . . . . . . . 7.2.2. Definition of X-VSPT(i, d) . . . . . . . . . . . . . . 7.2.3. P2MP-BRPC Procedure . . . . . . . . . . . . . . . . . . 7.2.4. P2MP-BRPC Procedure Completion Failure . . . . . . . . 7.2.5. P2MP-BRPC Example . . . . . . . . . . . . . . . . . . . 7.3. Using Core Tree Based Path Computation . . . . . . . . . . 7.3.1. Core Tree Procedure . . . . . . . . . . . . . . . . . . 7.3.2. Core Tree Procedure Completion Failure . . . . . . . . 7.3.3. Core Tree Example . . . . . . . . . . . . . . . . . . . 8. PCEP Protocol Extensions . . . . . . . . . . . . . . . . . . . 8.1. P2MP-BRPC Procedure . . . . . . . . . . . . . . . . . . . . 8.1.2 VSPT Encoding . . . . . . . . . . . . . . . . . . . . . 8.2 Core Tree Procedure . . . . . . . . . . . . . . . . . . . . 8.2.1. The Extension of RP Object . . . . . . . . . . . . . . 8.2.2 The PCE Sequence Object . . . . . . . . . . . . . . . . 9. Manageability Considerations . . . . . . . . . . . . . . . . . 9.1. Control of Function and Policy . . . . . . . . . . . . . . 9.2. Information and Data Models . . . . . . . . . . . . . . . 9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 9.4. Verifying Correct Operation . . . . . . . . . . . . . . . 9.5. Requirements on Other Protocols and Functional Components . . . . . . . . . . . . . . . . . . . . . . . . 9.6. Impact on Network Operation . . . . . . . . . . . . . . . 10. Security Considerations . . . . . . . . . . . . . . . . . . . 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1. Normative References . . . . . . . . . . . . . . . . . . . 13.2. Informative References . . . . . . . . . . . . . . . . . . Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . Contributors' Addresses . . . . . . . . . . . . . . . . . . . . . Zhao, et al. [Page 3] Internet-Draft October 2009 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]. 1. Terminology Terminology used in this document ABR: Area Border Routers. Routers used to connect two IGP areas (areas in OSPF or levels in IS-IS). ASBR: Autonomous System Border Routers. Routers used to connect together ASes of the same or different Service Providers via one or more Inter-AS links. Boundary Node (BN): a boundary node 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: The core tree is a P2MP tree where the root is the ingress LSR, the transit node and branch node are the BNs of the transit domains and the leaf nodes are the leaf BNs of the leaf domains. Destination: The leaf nodes can be in Root Domain, Transit Domain and Leaf Domain. 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. Inter-AS TE LSP: A TE LSP that crosses an AS boundary. Inter-area TE LSP: A TE LSP that crosses an IGP area boundary. P2MP LSP Path Tree: A 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. Root Boundary Node: The egress LSR from the root domain on the path of the P2MP LSP. Root Domain: The domain that includes the ingress (root) LSR. TED: Traffic Engineering Database. Transit/branch Domain: A domain that has an upstream and one or more downstream neighbour domain. Zhao, et al. [Page 4] Internet-Draft October 2009 Leaf Domain: A domain that doesn't have a downstream neighbor domain. Leaf Boundary Nodes: The entry boundary node in the leaf domain. Leaf Nodes: The LSRs that contain the P2MP LSP's final destinations. OF: Objective Function: A set of one or more optimization criterion (criteria) used for the computation of a single path (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 Domain Sequence: The known sequence of domains for a path between the ingress LSR and a leaf node. PCE Sequence: The known sequence of PCEs for calculating a path between the ingress LSR and leaf node. PCE Topology Tree: A list of PCE Sequences which has all the PCE Sequence for each path of the P2MP LSP path tree. PCE(i) is a PCE with the scope of domain(i). VSPT: Virtual Shortest Path Tree. X-VSPT: Extended Virtual Shortest Path Tree. This document also uses the terminology defined in [RFC4655], [RFC4875], [RFC5440], and [RFC5441]. 2. Introduction Multicast services are increasingly in demand for high-capacity applications such as multicast VPNs, IPTV (on-demand or streaming), and content-rich media distribution (for example, software distribution, financial streaming, or data-sharing). 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. A domain can be defined as a collection of network elements within a common sphere of address management or path computational responsibility such as an IGP area or an Autonomous Systems. The applicability of the Path Computation Element (PCE) for the computation of such paths is discussed in [PCE-P2MP-APP], and the requirements placed on PCEP for this are given in [PCE-P2MP-REQ]. Zhao, et al. [Page 5] Internet-Draft October 2009 [Editors Note] This draft proposes multiple techniques, including extending the technique specified in [RFC5441] for P2MP LSP path computation in an inter-domain environment using PCE [RFC4655]. As this document evolves and requirements are discussed, a single solution will ultimately be selected, which will define a PCE- based solution capable of computing an optimal inter-domain P2MP TE LSP. 2.1 Computing a P2MP Tree A P2MP tree is a graphical representation of all TE links that are committed for a particular P2MP LSP. In other words, a P2MP tree is a representation of the corresponding tunnel on the TE network topology. A sub-tree is a part of the P2MP tree describing how the root or an intermediate P2MP LSPs minimizes packet duplication when P2P TE sub-LSPs traverse common links. The computation of a P2MP tree requires three major pieces of information. The first is the path from the ingress LSR of a P2MP LSP to each of the egress LSRs, the second is the traffic engineering related parameters, and the third is the branch capability information. Generally, inter-domain P2MP tree (i.e. whose source and destinations of the P2MP LSP reside in a multiple different domains) is particularly difficult to compute even for a distributed PCE architecture. For instance, while the BRPC recursive path computation 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 a multiple ingress and/or egress border nodes, there is currently no known technique for one domain to determine which border routers another domain will utilize for the inter-domain P2MP tree, and to limit the computation of the P2MP tree to those utilized border nodes. A trivial solution to 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 Steiner P2MP tree. This, however, may require replication of incoming packets to all the P2P LSPs at the ingress PE to accommodate multipoint communication. Obviously, this solution is very inefficient for a couple of reasons. First, it places more replication burden on the ingress PE and hence has poor scaling characteristics, and second it does not make use of bandwidth sharing when one or more S2L LSPs share links along their paths, hence wasting bandwidth resources, memory and MPLS label space in the network. Zhao, et al. [Page 6] Internet-Draft October 2009 Apart from path computation difficulties faced due to the inter- domain topology visibility issues, the computation of the minimum P2MP Steiner tree, i.e. one 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, the frequent Steiner I tree computation process may prove computationally intensive, and the resulting frequent tunnel reconfiguration may even cause network destabilization. There are several heuristic algorithms presented in the literature that approximate the result within polynomial time that are applicable within the context of a single-domain. 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 GMPLS networks. The PCE is identified as a suitable application for the computation of paths for P2MP TE LSPs [PCE-P2MP-APP]. The draft-ietf-pce-brpc-09.txt specifies a procedure relying on the use of multiple Path Computation Elements (PCEs) to compute point-to- point (P2P) inter-domain shortest constrained paths across a predetermined sequence of domains, using a backward recursive path computation technique. The technique preserves confidentiality across domains, which is sometimes required when domains are managed by different Service Providers. The PCE communication protocol (PCEP) [RFC5440] is extended as a communication protocol between PCCs and PCEs for point-to- multipoint(P2MP) path computations and is defined in [PCE-P2MP-EXT]. However, that specification does not provide a mechanism to request path computation of inter-domain P2MP TE LSPs. This document presents a solution, and procedures and extensions to PCEP to support P2MP inter-domain path computation. 4. Assumptions It is assumed that due to deployment and commercial limitations (e.g., inter-AS peering agreements) the sequence of domains for a path (the path domain tree) will be known in advance. Zhao, et al. [Page 7] Internet-Draft October 2009 The examples and scenarios used in this document are also based on the following assumptions: - The PCE that serves each domain in the path domain tree is known and the set of PCEs and their relationships is propagated to each PCE during the first exchange of path computation requests; - Each PCE knows about any leaf LSRs in the domain it serves; - The boundary nodes to use on the LSP are pre-determined and form path of the path domain tree. In this version of the document we do not consider multi-homed domains. Additional assumptions are documented in [RFC5441] and will not be repeated here. 5. Requirements This section summarizes the PCEP requirements specific to computing inter-domain P2MP paths. In these requirements we note that the actual computation times by any PCE implementation are 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 LSP are changed. Its important that the solution preserves confidentiality across domains, which is sometimes required when domains are managed by different Service Providers. A number of specific requirements are detailed below: 1. The requirements specified in [RFC5376]; 1.1 PCEP must allow an SP to hide from other SPs the set of hops within its own ASes that are traversed by an inter-AS inter-provider TE LSP for each inter-AS TE LSP path segment an inter-AS PCE computes, it may return to the requesting inter-AS PCE an inter-AS TE LSP path segment from its own ASes without detailing the explicit intra-AS hops. 2. A number of additional requirements have also been identified in [RFC4461]. Zhao, et al. [Page 8] Internet-Draft October 2009 3. The computed P2MP LSP should be optimal when only considering The paths among the BNs. 4. Grafting and pruning of multicast destinations in a domain should have no impact on other domains and on the paths among BNs. 5. The complexity of the computing for each sub-tree within each domain should be only dependent on the topology of the domain and it should be independent of the domain sequences. 6. The number of PCEP request and reply messages should be independent of the number of multicast destinations in each domain. 6. Objective Functions During 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 requested. The computation of one or more P2MP TE-LSPs maybe subject to an OF in order to select the "best" candidate paths. A variety of objective functions have been identified as being important during the computation of inter-domain P2MP LSPs. These are: 1. The sub-tree within each domain should be optimized. 1.1 Minimum cost tree [PCE-P2MP-REQ]. 1.2 Shortest path tree [PCE-P2MP-REQ]. 2. The P2MP LSP paths should be optimal while only considering the entry and exit nodes of each domain as the transit, branch and leaf nodes of the P2MP LSP path. (That is, the Core Tree should be optimized.) 3. It should be possible to limit the number of entry points to a domain. 4. It should be possible to force the branches for all leaves within a domain to be in that domain. 7. Protocol Procedures The following sections describe the procedures to satisfy the requirements specified in the previous section. Zhao, et al. [Page 9] Internet-Draft October 2009 7.1. Per Domain P2MP Path Computation Computing P2P LSPs individually is an acceptable solution for computing a P2MP tree. 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 LSPs does not guarantee to produce a least-cost tree. This approach may be considered to have scaling issues during LSP setup. That is, the LSP to each leaf is signaled separately, and each border node must perform path computation for each leaf. A per doman solution does suit simply-connected domains and where the preferred points of interconnection are known. 7.2. Extending BRPC for P2MP Computation This section describes the extension to BRPC procedure defined in [RFC5441]. It also details procedure on how extended BRPC can be used for path computation of a P2MP LSP. 7.2.1. Definition of X-VSPT(i) Definition of X-VSPT(i) is similar to definition of VSPT(i) n [RFC5441], with a few exceptions outlined in the following. In the case of computation of VSPT(i), PCE(i) only considers the entry BNs of domain(i). That is only the BNs that provide connectivity from domain(i-1). This works well in P2P case as there is only one destination and there is no added value in knowing connectivity from BNs that do not provide connectivity from domain(i-1). However, for the case of P2MP tree path computation, and since there is usually more than one destination per P2MP LSP (some residing in different destination domains) knowing the connectivity from BNs that are not connected with domain(i-1) is useful. Specifically, it improves the ability of the ingress PCE to compute lower cost P2MP trees by favoring paths for new destination that branch off existing sub-tree as opposed to shortest end-to-end P2P path from source to destination. The set of BN-ex of domain remains the same as defined in [RFC5441]. X-VSPT(i) is defined as follows- In each domain (i), o There is a set of X-en(i) all entry BNs, such that BN- en(k,i) is the kth entry BN of domain(i). o There is a set of Y-ex(i) exit BNs, such that BN- ex(k,i) is the kth exit BN of domain(i). Zhao, et al. [Page 10] Internet-Draft October 2009 VSPT(i), as defined in [RFC5441], for P2P LSP is a tree that provides a list of shortest paths from BN-en(1,i), BN-en(2,i), ... BN-en(j,i) to destination such that j <= [X-en(i)], where [X-en(i)] is the number of entry BNs in domain(i). The X- VSPT(i), in addition to VSPT(i), includes shortest paths from the BN-en(k,i) to all BN-ex(i), such that k is the BN that is along the shortest path to destination, and BN-ex(i) is an exit BN in domain (i). Nonetheless, the X-VSPT(i) may exclude some BN-ex(i) according to policy constraints (either due to local policy or policies signaled in the path computation request). Also, when more than one BN-ex(i) connect to the same neighboring domain (domain (i+1)), the X-VSPT(i) only includes the BN-ex along the least cost path to domain (i+1). In the presence of inter-AS link, the X-VSPT includes the path of the inter-AS TE links connecting domain(i) to domain(i+1). For destination domain, the X-VSPT(i) includes shortest paths from the destination node to the set of BN-ex nodes. 7.2.2. Definition of X-VSPT(i, d) X-VSPT(i, d) is defined as X-VSPT at domain(i) to reach destination d of a P2MP tree. 7.2.3. P2MP-BRPC Procedure In the following section we outline steps of the P2MP-BRPC procedure. Given a set of destinations D = 1, 2, ... d, where |D| is the total number of destinations in the P2MP LSP. This draft assumes that the ingress PCE, PCE(1), has a mechanism to determine the set of PCEs (i.e. PCE-chain) to be traversed for the computation of the inter-domain path on per destination basis. The said mechanism is outside the scope of this document. Note, it is possible for the ingress PCE, PCE(1), to request path computation for destinations sequentially (one-by-one), or simultaneously (in-parallel). In the former case, the computation burden in P2MP-BRPC can be further reduced. PCE(1) can include the P2MP sub-tree(d-1), which includes X-VSPT(1, 1), X-VSPT(1, 2), ..., X-VSPT(1, d-1), i.e. that for destinations up to (d-1), in the PCE request for destination (d). By doing so, it is possible for PCE(n^d, d) to immediately compute a best path for (d) by computing a path from (d) to the closest branching node within the P2MP sub-tree(d-1). However, in this version of the draft only parallel requests for computation of XVSPT(n^d, d) for d = 1, 2, . . . D are considered. Zhao, et al. [Page 11] Internet-Draft October 2009 Denote by PCE(n^d, d) the PCE in the destination domain(n) of destination (d). A PCC discovers a PCE, PCE(1), that is capable of serving its path computation request and forwards to it the P2MP path computation request. PCE(1) will then iteratively send P2MP path requests to all destinations d = 1, 2, ... D, in the P2MP tree, as follows: Start of iteration(d): Step (1, d): PCE(1) forwards the P2MP path computation Request such that it traverses a set of PCE(s) until it reaches PCE(n^d, d). Step (2, d): PCE(n^d, d) computes X-VSPT(n^d, d) by including, in addition to VSPT(i), constraints shortest paths from the destination node (d) to all exit BNs BN- ex(i), as described earlier. When multiple BN-ex(n^d) connect to the same neighboring domain (domain (n^d +1)), the X-VSPT(n^d) only includes the BN-ex along the least cost path to domain (n^d +1). In the presence of inter-AS link, the X-VSPT includes the path of the inter-AS TE links connecting domain(n^d) to domain(n^d+1). Step (3, d): X-VSPT(n^d) is forwarded to PCE((n-1)^d,d). According to [RFC5441], PCE((n-1)^d) computes VSPT((n- 1)^d) by finding constrained shortest paths from all BN- en((n-1)^d) to the destination (d) using VSPT((n)^d). When this step is completed, only a sub-set of BN- en((n)^d) are selected. At this point, PCE((n-1)^d,d) can prune X-VSPT(n-1) to exclude those BN-en (and the respective X-VSPT((n)^d) branches attached to them) that were not considered in computation of VSPT((n-1)^d), and the respective X-VSPT((n)^d) branches attached to them. PCE((n-1)^d,d) appends to VSPT((n-1)^d) the X-VSPT((n- 1)^d) by by finding constrained shortest paths from all BN-en((n-1)^d) to all other BN-ex((n-1)^d). When multiple BN-ex((n-1)^d) connect to the same neighboring domain, the X-VSPT((n-1)^d) only includes the BN-ex along the least cost path to that domain. Step(i,d): the previous procedure is repeated PCE(i^d,d) where i= n-1 ... 2. End of iteration Zhao, et al. [Page 12] Internet-Draft October 2009 When PCE(1) receives replies with X-VSPTs(2,d) for all destinations, it forms a virtual graph composed of the source node, BNs included in the X-VSPTs, and the destinations. PCE(1) can then use a suitable heuristic to compute a feasible P2MP tree. Note, an X-VSPT(i, d) tree may be returned in the form of an explicit path (in which case all the hops along the path segment are listed) or a loose path (in which case only the BN is specified) so as to preserve confidentiality along with the respective cost. In the later case, various techniques can be used in order to retrieve the computed explicit paths on a per domain basis during the signaling process thanks to the use of path keys as described in [RFC5520]. 7.2.4. P2MP-BRPC Procedure Completion Failure To be described in a later version of this document. 7.2.5. P2MP-BRPC Example To be described in a later version of this document. 7.3. Using Core Tree Based Path Computation A core tree based solution provides an optimal inter-domain P2MP TE LSP and meets the requirements and OFs outlined in previous sections. A core tree is a path tree with nodes from each domain corresponding to the PCE topology which satisfies the following conditions: - The root of the core tree is the ingress LSR in the root domain; - The leaf of the core tree is the entry node in the leaf domain; - The transit and branch nodes of the core tree are from the entry and exit nodes from the transit and branch domains. 7.3.1 Core Tree Procedure Computing the complete P2MP LSP path tree is done in two phases: Procedure Phase 1: Build the P2MP LSP Core Tree. The algorithms to compute the optimal large core tree are outside scope of this document. In the case that the number of domains and the number of BNs are not big, the following extended BRPC based procedure can be used to compute the core tree. Zhao, et al. [Page 13] Internet-Draft October 2009 BRPC Based Core Tree Path Computation Procedure (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 a set of paths, we call it a 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. Procedure Phase 2: Grafting destinations to the P2MP LSP Core Tree. 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 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 the phase 1. 7.3.2. Core Tree Procedure Completion Failure To be described in a later version of this document. 7.3.3. Core Tree Example To be described in a later version of this document. 8. PCEP Protocol Extensions 8.1. P2MP-BRPC Procedure The X-BRPC procedure proposed in this document requires the specification of a new flag of the RP object carried within the PCReq message (defined in [RFC5440]), as follows X-VSPT Flag Bit Number Name Flag TBD X-VSPT When set, the VSPT Flag indicates that the PCC requests the computation of an inter-domain P2MP-TE TE LSP using the X-BRPC procedure defined in this document. Zhao, et al. [Page 14] Internet-Draft October 2009 8.1.2 VSPT Encoding Similar to the VSPT, the X-VSPT can be returned within a PCRep message. The encoding may consist of non-ordered lists of EROs where each ERO represents a path segment from a entry BN to the exit BNs, or from destination to an exit BN as described earlier in Section 7.2.3. Encoding using SERO is to be considered in the later version of this document. 8.2 Core Tree Based Procedure The following section describes the protocol extensions for Core Tree based inter-domain P2MP path calculation. 8.2.1. The Extension of RP Object The extended format of the RP object body to include the C bit 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. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |C|O|B|R| Pri | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Request-ID-number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: RP Object Body Format The following flags are added in this draft: o C ( 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 should have the Core Tree passed along with the destinations which and then graphed to the tree. Zhao, et al. [Page 15] Internet-Draft October 2009 8.2.2 The PCE Sequence Object The PCE Sequence Object is added to the existing PCE protocol. A list of this objects will represent the PCE topology tree. A list of Sequence Objects can be exchanged between PCEs during the PCE capability exchange or on the first path computation request message between PCEs. In this case, the request message format needs to be changed to include the list of PCE Sequence Objects for the PCE inter-domain P2MP calculation request. Each PCE Sequence can be obtained from the domain sequence for a specific path. All the PCE sequences for all the paths of P2MP inter-domain form the PCE Topology Tree of the P2MP LSP. The format of the new PCE Sequence Object for IPv4 (Object-Type 3) is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Object-Class | OT |Res|P|I| Object Length (bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for root PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | !! | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the PCE corresponding to the leafDomain | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: The New PCE Sequence Object Body Format for IPv4 The format of the new PCE Sequence Object for IPv6 (Object-Type 3) is as follows: Zhao, et al. [Page 16] Internet-Draft October 2009 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Object-Class | OT |Res|P|I| Object Length (bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for root PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | !! | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for the PCE corresponding to the leafDomain | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: The New PCE Sequence Object Body Format for IPv6 9. Manageability Considerations [PCE-P2MP-REQ] describes various manageability requirements in support of P2MP path computation when applying PCEP. This section describes how manageability requirements mentioned in [PCE-P2MP-REQ] 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 [PCE-P2MP P2MP] are already covered there. 9.1. Control of Function and Policy In addition to configuration parameters listed in [RFC5440], the following parameters MAY be required. o P2MP path computations enabled or disabled. o Advertisement of P2MP path computation capability enabled or disabled (discovery protocol, capability exchange). 9.2. Information and Data Models As described in [PCE-P2MP-REQ], MIB objects MUST be supported for PCEP extensions specified in this document. 9.3. Liveness Detection and Monitoring There are no additional considerations beyond those expressed in [RFC5440], since [PCE-P2MP-REQ] does not address any additional requirements. Zhao, et al. [Page 17] Internet-Draft October 2009 9.4. Verifying Correct Operation There are no additional considerations beyond those expressed in [RFC5440], since [PCE-P2MP-REQ] does not address any additional requirements. 9.5. Requirements on Other Protocols and Functional Components As described in [PCE-P2MP-REQ], the PCE MUST obtain information about the P2MP signaling and branching capabilities of each LSR in the network. Protocol extensions specified in this document does not provide such capability. Other mechanisms MUST be present. 9.6. Impact on Network Operation It is expected that use of PCEP extensions specified in this document will not have significant impact on network operations. 10. Security Considerations As described in [PCE-P2MP-REQ], P2MP path computation requests are more CPU-intensive and also use more link bandwidth. Therefore, it may be more vulnerable to denial of service attacks. Therefore it is more important that implementations conform to security requirements of [RFC5440], and the implementer utilize those security features. 11. IANA Considerations A new flag of the RP object (specified in [RFC5440]) is defined in this document. X-VSPT Flag Bit Number Name Flag Reference TBD X-VSPT This document. A number of additional IANA considerations exist and this section will highlight those requests in future versions of this document. 12. Acknowledgements The authors would like to thank Adrian Farrel and Dan Tappan for their valuable comments on this draft. Zhao, et al. [Page 18] Internet-Draft October 2009 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. [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)", RFC 4875, May 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. [RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel, "Preserving Topology Confidentiality in Inter-Domain Path Computation Using a Path-Key-Based Mechanism", RFC 5520, April 2009. [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. [RFC5541] Roux, J., Vasseur, J., and Y. Lee, "Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)", RFC5541, June 2009. 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. [RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)", RFC 5376, November 2008. Zhao, et al. [Page 19] Internet-Draft October 2009 [PCE-P2MP-APP] Yasukawa, S. and A. Farrel, "Applicability of the Path Computation Element (PCE) to Point-to-Multipoint (P2MP)Multiprotocol Label Switching (MPLS)and Generalized MPLS (GMPLS) Traffic Engineering (TE)", draft-ietf-pce-p2mp-app-02 (work in progress), February 2009. [PCE-P2MP-REQ] Yasukawa, S. and A. Farrel, "PCC-PCE Communication Requirements for Point to Multipoint Multiprotocol Label Switching Traffic Engineering (MPLS-TE)", draft-yasukawa-pce-p2mp-req-05 (work in progress), May 2008. [PCE-P2MP-EXT] Takeda, T., Chaitou M., Le Roux, J.L., Ali Z., Zhao, Q., King, D., "draft-ietf-pce-pcep-p2mp-extensions-04,work in progress, October , 2008. Authors' Addresses Quintin Zhao Huawei Technology 125 Nagog Technology Park Acton, MA 01719 US Email: qzhao@huawei.com Zafar Ali Cisco Systems, Inc. US Email: zali@cisco.com Tarek Saad Cisco Systems, Inc. US Email: tsaad@cisco.com Daniel King Old Dog Consulting UK Email: daniel@olddog.co.uk Zhao, et al. [Page 20] Internet-Draft October 2009 Contributors' Addresses David Amzallag British Telecommunications plc UK Email: david.Amzallag@bt.com Fabien Verhaeghe Thales Communication France 160 Bd Valmy 92700 Colombes FR Email: fabien.verhaeghe@gmail.com Kenji Kumaki KDDI R&D Laboratories, Inc. JP Email: ke-kumaki@kddi.com Zhao, et al. [Page 21] Internet-Draft October 2009