Internet Engineering Task Force H. Chen Internet-Draft Huawei Technologies Intended status: Standards Track July 11, 2011 Expires: January 12, 2012 A Forward-Search P2MP TE LSP Inter-Domain Path Computation draft-chen-pce-forward-search-p2mp-path-01.txt Abstract This document presents a forward search procedure for computing Point-to-MultiPoint (P2MP) Traffic Engineering (TE) Label Switched Paths (LSPs) crossing a number of domains through using multiple Path Computation Elements (PCEs). In addition, extensions to the Path Computation Element Communication Protocol (PCEP) for supporting the forward search procedure are described. 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 January 12, 2012. Copyright Notice Copyright (c) 2011 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 Chen Expires January 12, 2012 [Page 1] Internet-Draft Forward Search P2MP Path July 2011 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Conventions Used in This Document . . . . . . . . . . . . . . 4 4. Forward Search P2MP Path Computation . . . . . . . . . . . . . 4 4.1. Overview of Procedure . . . . . . . . . . . . . . . . . . 4 4.2. Description of Procedure . . . . . . . . . . . . . . . . . 5 4.3. Comparing to BRPC . . . . . . . . . . . . . . . . . . . . 7 5. Extensions to PCEP . . . . . . . . . . . . . . . . . . . . . . 7 5.1. RP Object Extension . . . . . . . . . . . . . . . . . . . 8 5.2. PCE Object . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3. Candidate Node List Object . . . . . . . . . . . . . . . . 9 5.4. Node Flags Object . . . . . . . . . . . . . . . . . . . . 10 5.5. Rest Destination Nodes Object . . . . . . . . . . . . . . 10 5.6. Request Message Extension . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7.1. Request Parameter Bit Flags . . . . . . . . . . . . . . . 13 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 9.2. Informative References . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Chen Expires January 12, 2012 [Page 2] Internet-Draft Forward Search P2MP Path July 2011 1. Introduction This document describes a new method called "Forward Search Shortest P2MP LSP Path Crossing Domains". The major characteristics of this method for computing an MPLS TE P2MP LSP path from a source node to a number of destination nodes crossing multiple domains include the following three ones. (1) It guarantees that the path computed from the source node to the destination nodes is shortest. (2) It does not depend on any domain path tree or domain sequences from the source node to the destination nodes. (3) Navigating a mesh of domains is simple and efficient. 2. Terminology ABR: Area Border Router. Routers used to connect two IGP areas (areas in OSPF or levels in IS-IS). ASBR: Autonomous System Border Router. 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. 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-area TE LSP: A TE LSP that crosses an IGP area boundary. Inter-AS TE LSP: A TE LSP that crosses an AS boundary. LSP: Label Switched Path. LSR: Label Switching Router. PCC: Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element. PCE: Path Computation Element. An entity (component, application, or Chen Expires January 12, 2012 [Page 3] Internet-Draft Forward Search P2MP Path July 2011 network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. PCE(i) is a PCE with the scope of domain(i). TED: Traffic Engineering Database. This document uses terminologies defined in RFC5440. 3. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119. 4. Forward Search P2MP Path Computation This section gives an overview of the forward search P2MP path computation procedure and describes the procedure in details. 4.1. Overview of Procedure Simply speaking, the idea of the Forward Search P2MP inter-domain path computation method for computing a path for an MPLS TE P2MP LSP crossing multiple domains from a source node to a number of destination nodes includes: Start from the source node and the source domain. Consider the optimal path segment from the source node to every exit boundary node of the source domain as a special link; Consider the optimal path segment from an entry boundary node to every exit boundary node of a domain as a special link; and the optimal path segment is computed as needed. The whole topology consisting of many domains can be considered as a special topology, which contains those special links, the normal links in the destination domains and the inter-domain links. Compute a shortest path in this special topology from the source node to the multiple destination nodes using CSPF. Forward Search P2MP inter-domain path computation method running at any PCE just grows the result path list/tree in the same way as normal CSPF on the special topology. When the result path list/tree Chen Expires January 12, 2012 [Page 4] Internet-Draft Forward Search P2MP Path July 2011 reaches all the destination nodes, the shortest path from the source node to the destination nodes is found and a PCRep message with the shortest path is sent to the PCE/PCC that sends the PCReq message eventually. 4.2. Description of Procedure Suppose that we have the following variables: A current PCE named as CurrentPCE which is currently computing the path. A number of rest destination nodes named as RestDestinationNodes, which is the number of destination nodes to which shortest paths are to be found. RestDestinationNodes is initially the number of all the destination nodes of an MPLS TE P2MP LSP. A candidate node list named as CandidateNodeList, which contains the nodes through which the shortest path from the source node to a destination node may be. Each node C in CandidateNodeList has the following information: the cost of the path from the source node to node C, the previous hop node P and the link between P and C, the PCE responsible for C, and the flags for C. The flags include: bit D indicating that node C is a Destination node if it is set; bit S indicating that C is the Source node if it is set; bit E indicating that C is an Exit boundary node if it is set; bit I indicating that C is an entry boundary node if it is set; and bit N indicating that C is a Node in a destination domain if it is set. The nodes in CandidateNodeList are ordered by path cost. Initially, CandidateNodeList contains only a Source Node, with path cost 0, PCE responsible for the source domain, and flags with S bit set. A result path list or tree named as ResultPathTree, which contains the shortest paths from the source node to the boundary nodes or the nodes in the destination domains. Initially, ResultPathTree is Chen Expires January 12, 2012 [Page 5] Internet-Draft Forward Search P2MP Path July 2011 empty. The Forward Search path computation method for computing a path for an MPLS TE P2MP LSP crossing a number of domains from a source node to a number of destination nodes can be described as follows: Initially, a PCC sets RestDestinationNodes to the number of all the destination nodes of the MPLS TE P2MP LSP, ResultPathTree to empty and CandidateNodeList to contain the source node and sends a PCE responsible for the source domain a request with the source node, RestDestinationNodes, CandidateNodeList and ResultPathTree. When the PCE responsible for a domain (called current domain) receives a request for computing the path for the MPLS TE P2MP LSP, it checks whether the current PCE is the PCE responsible for the node C with the minimum cost in the CandidateNodeList. If it is, then remove C from CandidateNodeList and graft it into ResultPathTree; otherwise, a PCReq message is sent to the PCE for node C. Suppose that node C has Flags. The ResultPathTree is built from C in the following steps. If node C is a destination node (i.e., the Destination Node (D) bit in the Flags is set), then RestDestinationNodes is decreased by one. If RestDestinationNodes is zero (i.e., all the destinations are on the result path tree), then the shortest path is found and a PCRep message with the path is sent to the PCE/PCC which sends the request to the current PCE. If node C is in the destination domain (i.e., the Node in Destination domain (N) bit in the Flags is set), then for every node N connected to node C and not on ResultPathTree, it is merged into CandidateNodeList. The cost to node N is the sum of the cost to node C and the cost of the link between C and N. The PCE for node N is the current PCE. If node C is an Entry Boundary Node or Source Node (i.e., the Entry/ Incoming Boundary Node (I) bit or the Source Node (S) bit is set), then path segments from node C to every exit boundary node of the current domain that is not on the result path tree are computed through using CSPF and as special links. For every node N connected to node C through a special link (i.e., a path segment), it is merged into CandidateNodeList. The cost to node N is the sum of the cost to node C and the cost of the special link (i.e., path segment) between C and N. The PCE for node N is the current PCE. If node C is an Exit Boundary Node (i.e., the Exit Boundary Node (E) bit is set) and there exist inter-domain links connected to it, then Chen Expires January 12, 2012 [Page 6] Internet-Draft Forward Search P2MP Path July 2011 for every node N connected to C and not on the result path tree, it is merged into the candidate node list. The cost to node N is the sum of the cost to node C and the cost of the link between C and N. The PCE for node N is the PCE responsible for node N. If the CurrentPCE is the same as the PCE of the node with the minimum cost in CandidateNodeList, then the node is removed from CandidateNodeList, grafted to ResultPathTree, and the above steps are repeated; otherwise, the CurrentPCE sends the PCE a request with the source node, RestDestinationNodes, CandidateNodeList and ResultPathTree. 4.3. Comparing to BRPC RFC 5441 describes the Backward Recursive Path Computation (BRPC) algorithm or procedure for computing an MPLS TE P2P LSP path from a source node to a destination node crossing multiple domains. Comparing to BRPC, there are a number of differences between BRPC and the Forward-Search P2MP TE LSP Inter-Domain Path Computation. Some of the differences are briefed below. At first, BRPC is for computing a shortest path from a source node to a destination node crossing multiple domains. The Forward-Search P2MP TE LSP Inter-Domain Path Computation is for computing a shortest path from a source node to a number of destination nodes crossing multiple domains. Secondly, for BRPC to compute a shortest path from a source node to a destination node crossing multiple domains, we MUST provide a sequence of domains from the source node to the destination node to BRPC in advance. The Forward-Search P2MP TE LSP Inter-Domain Path Computation does not need any sequence of domains for computing a shortest inter-domain P2MP path. Moreover, for a given sequence of domains domain(1), domain(2), ... , domain(n), BRPC searches the shortest path from domain(n), to domain(n-1), until domain(1). Thus it is hard for BRPC to be extended for computing a shortest path from a source node to a number of destination nodes crossing multiple domains. The Forward-Search P2MP TE LSP Inter-Domain Path Computation calculates a shortest path in a special topology from the source node to the destination nodes using CSPF. 5. Extensions to PCEP The extensions to PCEP for Forward Search P2MP Inter-domain Path Computation include the definition of a new flag in the RP object, a Chen Expires January 12, 2012 [Page 7] Internet-Draft Forward Search P2MP Path July 2011 result path list/tree and a candidate node list in a request message. 5.1. RP Object Extension The following flag is added into the RP Object: The F bit is added in the flag bits field of the RP object to tell the receiver of the message that the request/reply is for Forward Search Path Computation. o F (Forward search Path Computation bit - 1 bit): 0: This indicates that this is not PCReq/PCRep for Forward Search Path Computation. 1: This indicates that this is PCReq or PCRep message for Forward Search Path Computation. The IANA request is referenced in Section below (Request Parameter Bit Flags) of this document. This F bit with the N bit defined in RFC6006 can indicate whether the request/reply is for Forward Search Path Computation of an MPLS TE P2MP LSP or an MPLS TE P2P LSP. o F = 1 and N = 1: This indicates that this is a PCReq/PCRep message for Forward Search Path Computation of an MPLS TE P2MP LSP. o F = 1 and N = 0: This indicates that this is a PCReq/PCRep message for Forward Search Path Computation of an MPLS TE P2P LSP. 5.2. PCE Object The figure below illustrates a PCE IPv4 object body (Object-Type=2), which comprises a PCE IPv4 address. The PCE IPv4 address object indicates the IPv4 address of a PCE , with which a PCE session may be established and to which a request message may be sent. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PCE IPv4 address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Chen Expires January 12, 2012 [Page 8] Internet-Draft Forward Search P2MP Path July 2011 The format of the PCE object body for IPv6 (Object-Type=2) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | PCE IPv6 address (16 bytes) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.3. Candidate Node List Object The candidate-node-list-obj object contains a list of candidate nodes. A new PCEP object class and type are requested for it. The format of the candidate-node-list-obj object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The following is the definition of the candidate node list. ::= [] ::= ::= [] [] [] The ERO in a candidate node contain just the path segment of the last link of the path, which is from the previous hop node of the tail end node of the path to the tail end node. With this information, we can graft the candidate node into the existing result path list or tree. Chen Expires January 12, 2012 [Page 9] Internet-Draft Forward Search P2MP Path July 2011 Simply speaking, a candidate node has the same or similar format of a path defined in RFC 5440, but the ERO in the candidate node just contain the tail end node of the path and its previous hop, and the candidate node may contain two new objects PCE and node flags. 5.4. Node Flags Object The Node Flags object is used to indicate the characteristics of the node in a candidate node list in a request or reply message for Forward Search Inter-domain Path Computation. The Node Flags object comprises a Reserved field, and a number of Flags. The format of the Node Flags object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |D|S|I|E|N| Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where o D = 1: The node is a destination node. o S = 1: The node is a source node. o I = 1: The node is an entry boundary node. o E = 1: The node is an exit boundary node. o N = 1: The node is a node in a destination domain. 5.5. Rest Destination Nodes Object The figure below is an illustration of an object called a number of destinations not in path tree/list , which comprises an Object Length field, a Class-num field, a C-type filed, and a number of destinations not in path. As shown, the value of Object Length field in the object may be 8, which is a length of the object in bytes; the value of Class-num field and the value of C-type field will be assigned by Internet Assigned Numbers Authority (IANA); and the value of the number of destinations not in path tree field comprises a number, which is the number of destinations that are not in the final path computed yet. Chen Expires January 12, 2012 [Page 10] Internet-Draft Forward Search P2MP Path July 2011 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 Length (8) | Class-num | C-type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Numbe of Destinations not in path tree | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.6. Request Message Extension Below is the message format for a request message with the extension of a result path list and a candidate node list: Chen Expires January 12, 2012 [Page 11] Internet-Draft Forward Search P2MP Path July 2011 ::= [] ::=[] ::= [] [] [] [] [[]] [] [] [] [] [] where: ::=[] ::= ::=[] [] [] [] contains a ::= [] ::= ::= [] [] [] Figure 1: The Format for a Request Message The definition for the result path list that may be added into a request message is the same as that for the path list in a reply message that is described in RFC5440. 6. Security Considerations The mechanism described in this document does not raise any new Chen Expires January 12, 2012 [Page 12] Internet-Draft Forward Search P2MP Path July 2011 security issues for the PCEP protocols. 7. IANA Considerations This section specifies requests for IANA allocation. 7.1. Request Parameter Bit Flags A new RP Object Flag has been defined in this document. IANA is requested to make the following allocation from the "PCEP RP Object Flag Field" Sub-Registry: Bit Description Reference 18 Forward Path Computation (F-bit) This I-D 8. Acknowledgement The author would like to thank Julien Meuric and others for their valuable comments on this draft. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 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. Chen Expires January 12, 2012 [Page 13] Internet-Draft Forward Search P2MP Path July 2011 9.2. Informative References [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. [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. Author's Address Huaimo Chen Huawei Technologies Boston, MA USA Email: Huaimochen@huawei.com Chen Expires January 12, 2012 [Page 14]