Network Working Group Seisho Yasukawa (NTT) Internet Draft
Dimitri Papadimitriou (Alcatel) Jean Philippe Vasseur (Cisco) Adrian Farrel (Old Dog) Yuji Kamite (NTT Communications) Markus Jork (Avici) Rahul Aggarwal (Juniper) Andrew G. Malis(Tellabs) Alan Kullberg (Motorola)Editor Expiration Date: MarchJune 2004 January 2004 October 2003Requirements for Point to Multipoint extension to RSVP-TE <draft-ietf-mpls-p2mp-requirement-00.txt><draft-ietf-mpls-p2mp-requirement-01.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Abstract This document presents a set of requirements for Point-to-Multipoint (P2MP) Traffic Engineering (TE) extensions to Multiprotocol Label Switching (MPLS). It specifies functional requirements for RSVP-TE in order to deliver P2MP applications over a MPLS TE infrastructure. It is intended that potential solutions, that specify RSVP-TE procedures for P2MP TE LSP setup, use these requirements as a guideline. It is not intended to specify solution specific details in this document. It is intended that the requirements presented in this document are not limited to the requirements of packet switched networks, but also encompass the requirements of L2SC, TDM, lambda and port switching networks managed by Generalized MPLS (GMPLS) protocols. Protocol solutions developed to meet the requirements set out in this document must be equally applicable to MPLS and GMPLS. Table of Contents 1. Introduction .................................................. 34 2. Definitions ................................................... 45 2.1 Acronyms .................................................. 45 2.2 Terminology ............................................... 45 2.3 Conventions ............................................... 56 3. Problem statements ............................................ 57 3.1 Motivation ................................................ 57 3.2 Requirements overview ..................................... 67 4. Application Specific Requirements ............................. 89 4.1 P2MP tunnel for IP multicast data ......................... 89 4.2 P2MP TE backbone network for IP multicast network ............ 9.........10 4.3 Layer 2 Multicast Over MPLS ...............................10...............................11 4.4 VPN multicast network .....................................10.....................................12 4.5 GMPLS network .............................................11.............................................13 5. RequirementsDetailed requirements for P2MP capability exptension ...................12TE extensions ..................13 5.1 P2MP LSP tunnels ..........................................12..........................................13 5.2 P2MP explicit routing .....................................12.....................................14 5.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes .13.15 5.4 P2MP TE LSP establishment, teardown, and modification mechanisms ................................................14................................................16 5.5 Failure Reporting and Error Recovery ......................14......................16 5.6 Record route of P2MP TE LSP tunnels .......................15.......................17 5.7 Call Admission Control (CAC) and QoS control mechanism of P2MP TE LSP tunnels .......................................15....................................18 5.8 ReroutingReoptimization of P2MP TE LSP ..................................16.............................18 5.9 IPv4/IPv6 support .........................................16.........................................19 5.10 P2MP MPLS Label ..........................................16..........................................19 5.11 Routing advertisement of P2MP capability .................17.................19 5.12 Multi-Area/AS LSP ........................................17........................................19 5.13 P2MP MPLS management .....................................17.....................................20 5.14 Scalability ..............................................20 5.15 Backwards Compatibility ..................................20 5.16 GMPLS ....................................................21 5.17 Requirements for Hierarchical P2MP TE LSPs ...............21 5.18 P2MP Crankback routing ...................................22 6. Security Considerations........................................17Considerations........................................22 7. Acknowledgements ..............................................17..............................................22 8. References ....................................................18....................................................22 8.1 Normative References ......................................22 8.2 Informational References ..................................23 9. Author's Addresses ............................................19............................................24 10. Intellectual Property Consideration ...........................26 11. Full Copyright Statement ......................................26 1. Introduction Existing MPLS Traffic Engineering (MPLS-TE) allows for strict QoS guarantees, resources optimization, and fast failure recovery but is limited to P2P applications. There are P2MP applications like Content Distribution, Interactive Multimedia and VPN multicast that would also benefit from these TE capabilities. This clearly motivates for enhancement of base MPLS-TE tool box in order to support P2MP applications. This document presents a set of requirements for Point-to-Multipoint (P2MP) Traffic Engineering (TE) extensions to Multiprotocol Label Switching (MPLS). It specifies functional requirements for RSVP-TE [RFC3209] in order to deliver P2MP applications over a MPLS TE infrastructure.TE. It is intended that potential solutions, that specify RSVP-TE procedures for P2MP TE LSP setup, use these requirements as a guideline. It is not intended to specify solution specific details in this document. It is intended that the requirements presented in this document are not limited to the requirements of packet switched networks, but also encompass the requirements of TDM, lambda and port switching networks managed by Generalized MPLS (GMPLS) protocols. Protocol solutions developed to meet the requirements set out in this document must be equally applicable to MPLS and GMPLS. Content Distribution (CD), Interactive multi-media (IMM), and VPN multicast are applications that are best supported with multicast capabilities. One possible solution would beway to map P2MP flows onto LSPs in a MPLS network is to setup multiple P2P TE LSPs, one to each of the required egress LSRs. This requires replicating incoming packets to all the P2P LSPs at the ingress LSR to accommodate multipoint communication. This is sub-optimal. It places the replication burden on the ingress LSR and hence has very poor scaling characteristics. It also wastes bandwidth resources, memory and MPLS (e.g. label) resources in the network. Hence, to provide TE for a P2MP application in an efficient manner in a large scale environemnt,large-scale environment, P2MP TE mechanisms are required.required specifically to support P2MP TE LSPs. Existing MPLS P2PTE mechanisms have to be enhanced to[RFC3209] do not support P2MP TE LSP setup.LSPs so new mechanisms must be developed. This should be achieved without running a multicast routing protocol in the network core and with maximum re-use of the existing MPLS protocols.protocols in particular MPLS Traffic Engineering. A P2MP TE LSP will be setupset up with TE constraints and will allow efficient packet replication at various branching points in the network. RSVP-TE will be used for setting up a P2MP TE LSP with enhancements to existing P2P TE LSP procedures. The P2MP TE LSP setup mechanism will include the ability to add/remove receivers to/from an existing P2MP TE LSP. Moreover, multicast traffic cannot currently benefit from P2P TE LSP. Hence, CAC for P2P TE LSP cannot take into account the bandwidth used for multicast traffic. P2MP TE will allow to count the bandwidth used by unicast and multicast traffic by means of CAC. The problem statement is discussed in the following section. This document discusses various applications that can use P2MP MPLS TE.TE LSP. Detailed requirements for the setup of a P2MP MPLS TE LSP using RSVP-TE are described. Application specific requirements are also described. 2. Definitions 2.1 Acronyms P2P: Point-to-point P2MP: Point-to-multipoint 2.2 Terminology The reader is assumed to be familiar with the terminology in [RFC3031] and [RFC3209]. P2MP TE LSP: A traffic engineered label switched path that has one unique ingress LSR (also referred to as the root) and more than one egress LSR (referred(also referred to as the leaf). P2MP path: The ordered set of LSRs and links that comprise the path of a P2MP LSP.TE LSP from its ingress LSR to all of its egress LSRs. This path may be viewed as a tree. sub-P2MP path: A sub-P2MP path is a portion of a P2MP path starting at a particular LSR that is a member of the P2MP path and includes ALL downstream LSRs that are also members of the P2MP path. A sub-P2MP path may be viewed as a sub-tree. P2P sub-LSP path: The path from the ingress LSR to a particular egress LSR. ingress LSR: ItThe LSR that is responsible for initiating the signaling messages that set up, modify and teardownup the LSP branch LSR: AP2MP TE LSP. egress LSR: One of potentially many destinations of the P2MP TE LSP. Egress LSRs may also be referred to as leaf nodes or leaves. bud LSR: An LSR that is an egress, but also has one or more directly connected downstream LSRs. branch LSR: An LSR that has more than one directly connected downstream LSR. A branch LSR receives a single MPLS frame, makes a duplicate of it, and sends each to downstream interfaces.graft LSR: AAn LSR that is already a member of the P2MP path and is in process of signaling a new sub-P2MP path. prune LSR: AAn LSR that is already a member of the P2MP path and is in process of tearing down an existing sub-P2MP path. egress LSR: One of potentially many destinations of the P2MP LSP. Note that in some P2MP paths, an egress LSR may also have one or more downstream LSRs. Such an egress LSR may also be referred to as a branch LSR.2.3 Conventions 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 . 3. Problem Statement 3.1 Motivation Content Distribution (CD), Interactive multi-media (IMM), and VPN multicast are applications that are best supported with multicast capabilities. IP Multicast provides P2MP communication. However, there are no Traffic Engineering (TE) capabilities or QoS guarantees with existing IP multicast protocols. Note that Diff-serv (see [RFC2475],[RFC2597] and [RFC3246]) combined with IP multicast routing ismay not be sufficient for P2MP applications for many of the same reasons that it is not sufficient for unicast applications TE and constraint basedapplications. Note also that multicast tree provided by existing IP multicast routing protocols are requirednot optimal, which may lead to enablesignificant bandwidth wasting. TE and scale the efficient management of network resources, mechanism to prevent congestion (includingConstraint Based Routing, including Call Admission Function combined withControl (CAC), explicit source routing, Diffserv),routing and bandwidth reservation, is required to enable sub-second reroutingefficient resource optimization, strict QoS guarantees, and fast recovery around network failures. Furthermore there are no existing P2MP mechanisms for carrying layer 2 or SONET/SDH multicast traffic over MPLS. TE capabilities are desirable for both these applications. One possible solution would be to setup multiple P2P TE LSPs, one to each of the required egress LSRs. This requires replicating incoming traffic to all the P2P LSPs at the ingress LSR to accommodate multipoint communication. This is clearly sub-optimal. It places the replication burden on the ingress LSR and hence has very poor scaling characteristics. It also wastes bandwidth resources, memory and MPLS (e.g. label) resources in the network. Hence, to provide MPLS TE [RFC2702] for a P2MP application in an efficient manner in a large scale environment, P2MP TE mechanisms are required. Existing MPLS P2P TE mechanisms have to be enhanced to support P2MP TE LSP setup.LSP. 3.2. Requirements Overview This document is proposing requirements for the setup of P2MP TE LSPs. This should be achieved without running a multicast routing protocol in the network core and with maximum re-use of the existing MPLS protocols. Note that the use of MPLS forwarding to carry the multicast traffic may also be useful in the context of some network design where it is being desired to avoid running some multicast routing protocol like PIM [PIM-SM] or BGP (which might be required for the use of PIM). A P2MP LSP will be setupset up with TE constraints and will allow efficient MPLS packet replication at various branching points in the network. RSVP-TE will be used for setting up a P2MP TE LSP with enhancements to existing P2P TE LSP procedures. The P2MP TE LSP setup mechanism will include the ability to add/remove receiversegress LSRs to/from an existing P2MP TE LSP and should support all the TE LSP management procedures defined for P2P TE LSP (like the non disruptive rerouting (so- the so called "Make before break" procedure). The computation of P2MP TE paths is implementation dependent and is beyond the scope of the solutions that are built with this document as a guideline. The MPLS WG will specify how to build solutions for the setup aP2MP TE LSP.LSPs. The usage of those solutions will be application dependent and is out of the scope of this draft. However, it is a requirement that those solutions be applicable to GMPLS as well as MPLS so that only a single set of solutions are developed. Consider the following figure. Source 1 (S1) | I-LSR1 | | | | R2----E-LSR3--LSR1 LSR2---E-LSR2--Receiver 1 (R1) | : R3----E-LSR4 E-LSR5 | : | : R4 R5 Figure 1.1 The abovefigure above shows I(Ingress)-LSR1, E(Egress)-LSR2, E-LSR3a single ingress (I-LSR1), and E-LSR4.four egresses (E-LSR2, E-LSR3, E-LSR4 and E-LSR5). I-LSR1 is attached to a traffic source that is generating traffic for a P2MP application. E-LSR2, E-LSR3Receivers:R1, R2, R3 and E-LSR4R4 are attached to receivers that are interested in receiving traffic for the application.E-LSR2, E-LSR3 and E-LSR4. The following are the objectives that we wish to achieve: a) A P2MP TE LSP path informationwhich satisfies various constrains is pre-determined and supplied to ingress I-LSR1. Note that no assumption is made on whether the path is provided to I-LSR1 or computed by I-LSR1. Typical constraints are bandwidth requirements, resource class affinities, fast rerouting, preemption, along with several potential other constraints.preemption. There should not be any restriction on the possibility to support the set of constraints already defined for point to point TE LSPs. b) Set up aA P2MP TE LSP is set up by means of RSVP-TE from I-LSR1 to E-LSR2, E-LSR3 and E-LSR4 using the path information which could have been computed by some off-line or on-line algorithms.information. c) In this case, the branch LSR1 should replicate incoming packets and send them to E-LSR3 and E-LSR4. d) The P2MP TE LSP should be setup by enhancing existing RSVP-TE P2P procedures and without any requirement for multicast routing protocol in the network core. e) The solution should provide the ability to gracefully modify P2MP TE LSP (i.e add/remove some part of the p2mp TE LSP without requiring to entirely tearing down or setting upIf a completelynew p2mp TE LSP). Such operations should be performedreceiver (R5) expresses an interest in receiving traffic, a non traffic disruptive fashion. In this case,new path is determined and a sub-P2MP path LSR2->E-LSR5from LSR2 to E-LSR5 is grafted and pruned based on traffic destination change.onto the P2MP path. LSR2 becomes a branch LSR. 4. Application Specific Requirements This section describes some of the applications that P2MP MPLS TE is applicable to along with application specific requirements, if any.requirements. The purpose of this section is not to mandate how P2MP TE LSPs must be used in certain application scenarios. Rather it is to illustrate some of the potential application scenarios so as to highlight the features and functions that any P2MP solution must provide in order to be of wide use and applicability. This section is not meant to be exhaustive and not limited to the described applications. 4.1 P2MP tunnelTE LSP for IP multicast data One typical scenario is to use P2MP TE LSPs as P2MP tunnels ofcarrying multicast data traffic (e.g. IP mcast). In this scenario, a P2MP TE LSP tunnelis established between an ingress LSR which accomodatessupports IP multicast source and several egress LSRs which accomodatesupport several IP multicast receivers. Instead of using an IP multicast routing protocol in the network core, a P2MP TE LSP tunnelis established over the network and IP multicast data are tunnelledtunneled from an ingress LSR node to multiple egress leaf LSRs with thedata replication at the branch LSRs in the network core. Figure 2 shows thisan example. Note that a P2MP TE LSP can be established over multiple AREAs/ASs.areas/ASs and that the egress LSRs may deliver data into an IP multicast network. Mcast Source | +---------------I-LSR0----------------+ | | | | LSR0 +----E-LSR2---R2 | / \ / | R1---E-LSR1---LSR2-----LSR1 LSR3----LSR4----E-LSR3---R3 | / \ \ | | / \ +----E-LSR4---R4 +-------B-LSR1---------B-LSR2---------+ +-------- / ------++------ \ ---------+ | | || | R5---E-LSR5--------LSR5 || IPmcast Network | | / \ || | +-E-LSR6---E-LSR7-++----MR0--MR1------+ | | | | R6 R7 R8 R9 Figure 2 4.2 P2MP TE backbone network for IP multicast network In this scenario,P2MP TE LSPs are utilized to constructapplicable in a P2MPbackbone network forto construct or support a multicast network (e.g.network(e.g. IPmcast network). EachThe IP multicast access networks isare interconnected by aP2MP TE LSP.LSPs. A P2MP TE LSP is established from an ingress LSR which accomodatesaccommodates an IP multicast network that has a Mcast Sourcemulticast source to multiple egress LSRs which accomodateeach accommodate an IP multicast network. In this scenario, ingress/egress LSRs placed at the edge of multicast network must handle an IP multicast routing protocol. This means that eachthe ingress/egress LSR exchangesLSRs exchange IP multicast routing messages as neighbour router.routers. Figure 3 shows a network example of this scenario. A P2MP TE LSP is established from a I-LSR1 to E-LSR2, E-LSR3, E-LSR4 and eachthe ingress/egress LSR exchanges the multicast routing messages with each other. As specified in the section on the problem statement it should be possible for a solution to add/remove egress LSRs to/from the P2MP MPLS TE LSP. IP multicast group membership distribution between the egress LSRs may change frequently. This in turn may require a potential P2MP MPLS TE solution, that is suitable for IP multicast, to handle additions/deletions of egress LSRs at a rapid rate.with an appropriate reactiveness. It is recommended to support a message exchange mechanism on top of P2MP LSP setup mechanism to support multicast (S, G) Join/ Leave and to allow the ingress LSR to hold sufficient information in order to optimise multicast FEC on sender nodes.Join/Leave. Though several schemes exist to handle this scenario, these are out of scope of this document. This document only describes requirements to setup a P2MP TE LSP. Mcast Source | +-----MR-----+ | | | | MR | +------|-----+ +---------------I-LSR1----------------+ | // ||| \\ | | // ||| \\ | | // |LSR| \\ | | ___//____/|_____\\____ | | / // ||| \\ \ | | | // ||| \\ | | +-----E-LSR2----E-LSR3-----E-LSR4-----+ +---- / ---++------|------++--- \ ----+ | | || | || | | R1---MR---MR || MR || MR__ | | / \ || / \ || / \ \MR---R8 +--MR--MR--++----MR--MR---++--MR--MR--+ | | | | | | R2 R3 R4 R5 R6 R7 Figure 3 4.3 Layer 2 Multicast Over MPLS Existing layer 2 networks offer multicast video services. These are typically carried using layer 2 NBMA technology such as ATM or layer 2 BABroadcast Access technology such as Ethernet. It may be desirable to deliver these layer 2 multicast services over a converged MPLS infrastructure where P2MP TE LSPs are used instead. 4.4 VPN multicast networkFor instance, several SPs provision P2MP ATM VCs for TV/ADSL services. These P2MP VCs are setup between a video server and a set of ATM DSLAMs. Each channel is carried in a distinct P2MP VC. These VC maybe be routed independently, or may all be nested into a unique PVC, connecting the video sever to all DSLAMs. Such service could benefit from a P2MP MPLS-TE control plane. An option is to setup a permanent P2MP TE LSP between the video server and all DSLAMs, that would correspond to a PVC carrying all channel VCs. In this case each DSLAM receives all channels, even if there are no receivers that are registered for a given channel. This ensure fast zapping, but lead to significant bandwidth wasting. A second option is to setup a distinct P2MP TE LSP per channel. If a client, behind a DSLAM, zaps to a new channel, then the DSLAM has to be added to the P2MP TE LSP carrying this channel using a P2MP TE grafting procedure. Pruning procedure has to be used to remove a DSLAM from the P2MP TE LSP if it is not already egress LSR for that LSP because all the clients, behind the DSLAM, stop watching the channel. 4.4 VPN multicast network In this scenario, P2MP TE LSPs are utilized to construct a provider network which can deliver VPN multicast service(s) to its customers. A P2MP TE LSP is established between all the PE routers which accommodate the customer private network(s) that handle the IP multicast packets. Each PE router must handle a VPN instance. For example, in Layer3 VPNVPNs like BGP/MPLS based IP VPNVPNs [BGP/MPLS IP VPNs], this means that each PE router must handle both private multicast VRF tables and common multicast routing and forwarding table. And each PE router exchanges private multicast routing information between the corresponding PE routers. It is desirable that P2MP MPLS TE can be used for Layer3 VPN'sVPN data transmission. Another example is a Layer2 VPN that supports multipoint LAN connectivity service. In an Ethernet network environment, IP multicast data is flooded to the appropriate Ethernet port(s). InAn Ethernet multipoint L2Layer2 VPN service provided by MPLS, this function is achieved by switching MPLS encapsulated frames towards the relevant PE nodes. But if existing P2P TE LSPs are used as tunnels between PEs, any ingress PE must duplicate the frames and thesend them to the corresponding PEs. This means the data stream is flooded just from the ingress PE, which will waste the provider's network resources. So, for Layer 2 VPNs,VPNs that are required to support multicast traffic, it is desirable that P2MP MPLS TE LSPs are used for data transmission instead of P2P MPLS TE LSPs, contributing in turn to savings of network resources. This document does not set requirements for how multicast VPNs are provided, but it does set requirements for the function that must be available in P2MP MPLS solutions. Therefore, it is not a requirement that multicast VPNs utilize P2MP MPLS, but it is a requirement that P2MP MPLS solutions should be capable of supporting multicast VPNs. 4.5 GMPLS NetworkNetworks GMPLS supports only P2P TE-LSPs just like MPLS. GMPLS enhances MPLS to support four new classes of interfacesinterfaces: Layer-2 Switch Capable (L2SC), Time-Division Multiplex (TDM), Lambda Switch Capable (LSC) and Fiber-Switch Capable (FSC) in addition to Packet Switch Capable (PSC) already supported by MPLS. All of these interface classes have so far been limited to P2P TE LSPs (see [RFC 3473] and [RFC 3471]). The requirement for P2MP services for non-packet switch interfaces is similar to that for PSC interfaces. In particular, cable distribution services such as video distribution are prime candidates to use P2MP features. Therefore, it is a requirement that all the features/mechanisms (and protocol extensions) that will be defined to provide MPLS P2MP TE LSPs will be equally applicable to P2MP PSC and non-PSC TE-LSPs. This also means that solutions5. Detailed requirements for MPLSP2MP TE-LSPs when applied to GMPLSTE extensions 5.1 P2MP PSC and non-PSC TE-LSPs shallLSP tunnels The P2MP RSVP-TE extensions MUST be backward and forward compatible with the other features of GMPLS including: o control and data plane separation (IF_ID RSVP_HOP and IF_ID ERROR_SPEC), o full support of numbered and unnumbered TE links (see [RFC 3477] and [GMPLS-ROUTING]), o use of the GENERALIZED_LABEL_REQUEST and the GENERALIZED_LABEL (C-Type 2 and 3) in conjunction with the LABEL_SET and the ACCEPTABLE_LABEL_SET object, o processing of the ADMIN_STATUS object, o processing of the PROTECTION object, o support of Explicit Label Control, o processing of the Path_State_Removed Flag, o handling of Graceful Deletion procedures. In addition, since non-PSC TE-LSPs may have to be processed in environments where the "P2MP capability" could be limited, specific constraints may also apply during the P2MP TE Path computation. Being technology specific, these constraints are outside the scope of this document. However, technology independent constraints (i.e. constraints that are applicable independently of the LSP class) should be allowed during P2MP TE LSP message processing. It has to be emphasized that path computation and management techniques shall be as close as possible than those being used for PSC P2P and P2MP TE LSPs. 5. Requirements for P2MP capability extension 5.1 P2MP LSP tunnels The P2MP RSVP-TE extensions MUST be applicable to signaling LSPsapplicable to signaling LSPs of different traffic types. For example, it must be possible to signal a P2MP TE LSP to carry any kind of payload being packet or non-packet based (including frame, cell, TDM un/structured, etc.) Carrying IP multicast or Ethernet traffic within a P2MP tunnel are typical examples. As with P2P MPLS technology[RFC3031],technology [RFC3031], traffic is classified with FEC in this extension. All packets which belong to a particular FEC and which travel from a particular node MUST follow the same P2MP path. In order to scale to a large number of branches, P2MP TE LSPs should be identified by unique identifier that is constant for the whole LSP regardless of the number of branches and/or leaves. Therefore, the identification of the P2MP session by its destination addresses is not adequate. 5.2 P2MP explicit routing Various optimizations in P2MP path formation need to be applied to meet various needs such asQoS requirements and operational constraints. Some P2MP applications may request a bandwidth guarantees,guaranteed P2MP path which satisfies end-to-end delay requirements, and minimization of the totalrequirements. And some operators may want to set up a cost minimum P2MP path cost.by specifying branch LSRs explicitly. The P2MP TE solution therefore MUST provide a means of establishing arbitrary P2MP paths.paths under the control of an external path computation process or path configuration process or dynamic path computation process located on the ingress LSR. Figure 4 shows two typical examples. A A | / \ B B C | / \ / \ C D E F G | / \ / \/ \ / \ D--E*-F*-G*-H*-I*-J*-K*--L H I J KL M N O Steiner P2MP path SPF P2MP path Figure 4 Examples of P2MP TE LSP topology One example is Steiner[STEINER] P2MP path (Cost minimum P2MP path). This P2MP path is suitable for constructing cost minimum P2MP path. To realize this P2MP path, several intermediate LSRs must be both MPLS data terminating LSR and transit LSR (LSR E, F, G, H, I, J, K, in the figure).figure 4). This means that the LSR must perform both label swapping and popping at the same time. Therefore, the P2MP TE solution MUST support a mechanism that can setup this kind of terminatebud LSR between aan ingress LSR and egress LSRs. Another example is CSPF (Constraint Shortest Path Fast) P2MP path. By some metric (which can be set upon any specific criteria like the delay, bandwidth, a combination of those), one can calculate a cost minimum P2MP path. This P2MP path is suitable for carrying real time traffic. To support explicit setup of any reasonable P2MP path shape, a P2MP TE solution mustMUST support some form of explicit source-based control of the P2MP path. Thispath which can be used byexplicitly include particular LSRs as branch nodes. This can be used by the ingress LSR to setup the P2MP TE LSP. Being implementation specific (more precisely dependent of the data structure specific representation and its processing), the detailed method for controlling the P2MP TE LSP topology depends on how the control plane represents the P2MP TE LSP data plane entity. For instance, a P2MP TE LSP can be simply represented as a whole tree or by its individual branches or as a whole.branches. Here also, effectiveness of the potential solutions is left outside the scope of this document. In any case, it is expected that this control must be driven by the ingress LSR. 5.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes A P2MP path is completely specified if all of the required branches and hops between a sender and leaf LSR are indicated. A P2MP path is partially specified if only a subset of intermediate branches and hops are indicated. This may be achieved using loose hops in the explicit path, or using widely scoped abstract nodes such as IPv4 prefixes shorter than 32 bits or AS numbers. A partially specified P2MP path may be particularly useful in inter-area and inter-AS situations. Protocol solutions SHOULD include a way to specify loose hops and widely scoped abstract nodes in the explicit source- based control of the P2MP path as defined in the previous section. Where this support is provided, protocol solutions MUST allow downstream LSRs to apply further explicit control to the P2MP path to resolve a partially specified path into a (more) completely specified path. Protocol solutions MUST allow the P2MP path to be completely specified at the ingress where sufficient information exists to allow the full path to be computed. In all cases, the egress nodes of the P2MP TE LSP must be fully specified. In case of path being computed by some downstream LSRs (e.g. case of hops specified as loose hops), the solution SHOULD provide the ability for the ingress LSR of the P2MP TE LSP to learn the full P2MP path. Note that this requirement may be relaxed in some environment (e.g. Inter-AS) where confidentiality must be preserved. 5.4 P2MP TE LSP establishment, teardown, and modification mechanisms The P2MP TE solution must support large scale P2MP TE LSPs establishment and teardown in a scalable manner. In addition to wholeP2MP TE LSP establishment and teardown mechanism, it SHOULD implement partial P2MP path modification mechanism. For the purpose of adding sub-P2MP TE LSPs for existing P2MP TE LSP, the extension SHOULD support grafting mechanism. For the purpose of deleting a sub-P2MP TE LSPs from existing P2MP TE LSP, the extension SHOULD support pruning mechanism. It is RECOMMENDED that these grafting and pruning operations do not cause any additional processing in nodes except along the path to the grafting and pruning node and its downstream nodes. Moreover, both grafting and pruning operations MUST not be traffic disruptive for the traffic currently forwarded along the P2MP path. 5.5 Failure Reporting and Error Recovery Failure events may cause egress nodes or sub-P2MP LSPs to become detached from the P2MP TE LSP. These events must be reported upstream as for a P2P LSP. Protection andThe solution SHOULD provide recovery techniques SHOULD be appliedsuch as protection and restoration allowing to therecover any impacted sub-P2MP TE LSPs. In particular, it is required to provide fast protection mechanisms applicable to P2MP TE LSP similar to build new sub-P2MPthe solutions specified in [FRR] for P2P TE LSPs. Note also that no assumption is made on whether backup paths for P2MP TE LSPs should or use backup sub-P2MPnot be shared with P2P TE LSPs backup paths. A P2MP TE solution MUST support P2MP fast protection mechanism to restore the datahandle P2MP applications sensitive to the severed egress nodes.traffic disruption. The report of the failure of delivery to fewer than all of the egress nodes SHOULD NOT cause automatic teardown of the P2MP TE LSP. That is, while some egress nodes remain connected to the P2MP path it should be a matter of local policy at the ingress whether the P2MP LSP is retained. When all egress node downstreams of a branch node have become disconnected from the P2MP path, and the some branch node is unable to restore connectivity to any of them through recovery or protection mechanisms, the branch node MAY remove itself from the P2MP path. Since the faults that severed the various downstream egress nodes from the P2MP path may be disperate,disparate, the branch node MUST report all such errors to its upstream neighbor. The ingress node can then decide to re-compute the path to that particular egress node, around the failure point. Solutions MAY include the facility for transit LSRs and particularly branch nodes to recompute sub-P2MP paths to restore them after failures. In the event of successful repair, no error notification is reported to upstream nodes, but the new paths are reported if route recording is in use. Crankback requirements are discussed in [CRANKBACK]. 5.6 Record route of P2MP TE LSP tunnels Being able to identify the established topology of P2MP TE LSP is very important for various purpose:Management, operation of some local recovery mechanism like Fast Reroute [FRR]. A network operator uses this information to manage P2MP TE LSP. Therefore, topology information MUST be collected and updated after P2MP TE LSP establishment and modification process. For this purpose, conventional Record Route mechanism is useful. As with other conventional mechanism, this information should be forwarded upstream towards the sender node. The P2MP TE solution MUST support a mechanism which can collect and update P2MP path topology information after P2MP LSP establishment and modification process. It is RECOMMENDED that those information are collected in a data format by which the sendorsender node can recognize the P2MP path topology without involving some complicated data calculation process. The solution MUST support the recording of both outgoing interfaces or node-id [NODE-ID]. 5.7 Call Admission Control (CAC) and QoS Control mechanism of P2MP TE LSP tunnels P2MP TE LSP share network resource with P2P TE LSP. Therefore it is important to use CAC and QoS as P2P TE LSP for easy and scalable operation. In particular, it should be highlighted that because mutliacstMulticast traffic cannot make use of point to point TE LSP, multicast traffic cannot be easily taken into account by point to point in order to perform CAC. The use of P2MP TE LSP will now allow for an accounting of the unicast and multicast traffic for bandwidth reservation. P2MP TE solution MUST both supports FF and SE reservation style. P2MP TE solution MUST be applicable to Diffserv-enabled network that can provide consistent QoS control in P2MP LSP traffic. This solution SHOULD also satisfy DS-TE requirement [RFC3564] and interoprableinteroperable smoothly with current P2P DS-TE protocol specification. 5.8 Rerouting ofNote that this requirement document does not make any assumption on the type of bandwidth pool used for P2MP TE LSP which can either be shared with P2P TE LSP or be dedicated. 5.8 Reoptimization of P2MP TE LSP The detection of a more opticaloptimal path and network resource failure(s) (such as link(s) and node(s)) are examplesis an example of situation where P2MP TE LSP re-routing is needed.may be required. While re-routing is in progress, an important requirement is avoiding traffic disruption. An additional requirement is avoidingdouble bandwidth reservation (over the common parts between the old and new LSP) throughthorough the use of resource sharing. Make-before-break (see [RFC 3209])[RFC3209]) delivers simultaneously a solution to these requirements. Make-Before-BreakMake-before-break MUST be supported for a P2MP TE LSP to ensure that there is no traffic disruption when the P2MP TE LSP is rerouted. AndThere is a P2MP TE solution MUST support P2MP fast rerouting mechanismpossibility to handle P2MP applications sensitiveachieve make-before-break that only applies to a sub-P2MP path without impacting the data on the all of the other parts of the P2MP path. The solution SHOULD allow for make-before-break reoptimization of a sub-tree with no impact on the rest of the tree (no label reallocation, no change in identifiers...). Such reoptimization MAY be initiated by the sub-tree root branch node. (e.g. the branch node setup a new sub-tree, then splices traffic disruption.on the new subtree and delete the former sub-tree). 5.9 IPv4/IPv6 support A P2MP TE solution MUST be applicable to IPv4/IPv6. 5.10 P2MP MPLS Label A P2MP TE solution MUST support establishment of both P2P and P2MP TE LSP and MUST NOT impede the operation of P2P TE LSPs within the same network. A P2MP TE solution MUST be specified in such a way that it allows P2MP and P2P TE LSPs to be signaled on the same interface. Labels for P2MP TE LSPs and P2P TE LSPs MAY be assigned from shared or dedicated label space(s). Label space shareability is implementation specific. 5.11 Routing advertisement of P2MP capability This document has identified several high-level requirements for enhancements to routing and signalling protocols to support P2MP MPLS. These are needed to facilitate the computation of P2MP paths using TE constraints so that explicit source-control may be applied to the LSP paths as they are signaled through the network. These requirements include but not restricted to: - the ability of an LSR to support branchingbranching. - the ability of an LSR to act as an egress and a branch for the same LSP. The applicability of these requirements is for further study. These requirements are developed in a separate document. 5.12 Multi-Area/AS LSP P2MP TE solution SHOULD support multi-Area/AS LSP. A separate document may deal with the specifics of inter-area and inter-AS P2MP TE LSPs. 5.13 P2MP MPLS management The MPLS MIB should be enhanced to provide P2MP TE LSP management. P2MP TE LSPs MUST have a unique identifier whose definition MAY be partially or entirely shared with P2P TE LSP identifiers used for management purposes. 6. Security Considerations Security considerations will5.14 Scalability Scalability is a key requirement in P2MP MPLS systems. Solutions should be addresseddesigned to scale well with an increase in a future revisionthe number of this document. 7. Acknowledgements The authors would like to thank George Swallow, Ichiro Inoue and Dean Cheng for his reviewany of the following: the number of recipients, the number of branch points and suggestionthe number of an earlier draftbranches. Both scalability of this document. 8. References [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.performance and G. Swallow, "RSVP-TE: Extensionsoperation must be considered. Key considerations may include: - the amount of refresh processing associated with maintaining a P2MP TE LSP. - the amount of protocol state that must be maintained by transit LSRs along a P2MP path. - the number of protocol messages required to RSVP for LSP Tunnels", RFCset up or tear down a P2MP LSP as a function of the number of egress LSRs. - the number of protocol messages required to repair a P2MP LSP after failure or perform make-before-break. - the amount of protocol information transmitted to manage a P2MP TE LSP (i.e. the message size). - the amount of potential routing extensions. - the amount of control plane processing required by the ingress, transit and egress LSRs to add/delete a branch LSP to/from an existing P2MP LSP. 5.15 Backwards Compatibility It should be an aim of any P2MP solution to offer as much backward compatibility as possible. An ideal would be to offer P2MP services across legacy MPLS networks without any change to any LSR in the network. If this ideal cannot be achieved, the aim should be to use legacy nodes as both transit non-branch LSRs and egress LSRs. It is a further requirement of all protocol solutions that any LSR that implements the solution shall not be prohibited by that act from supporting P2P TE LSPs using existing signaling mechanisms. That is, unless administratively prohibited, P2P TE LSPs must be supported through a P2MP network. 5.16 GMPLS Solutions for MPLS P2MP TE-LSPs when applied to GMPLS P2MP PSC or non-PSC TE-LSPs must be backward and forward compatible with the other features of GMPLS including: o control and data plane separation (IF_ID RSVP_HOP and IF_ID ERROR_SPEC), o full support of numbered and unnumbered TE links (see [RFC 3477] and [GMPLS-ROUTING]), o use of the GENERALIZED_LABEL_REQUEST and the GENERALIZED_LABEL (C-Type 2 and 3) in conjunction with the LABEL_SET and the ACCEPTABLE_LABEL_SET object, o processing of the ADMIN_STATUS object, o processing of the PROTECTION object, o support of Explicit Label Control, o processing of the Path_State_Removed Flag, o handling of Graceful Deletion procedures. In addition, since non-PSC TE-LSPs may have to be processed in environments where the "P2MP capability" could be limited, specific constraints may also apply during the P2MP TE Path computation. Being technology specific, these constraints are outside the scope of this document. However, technology independent constraints (i.e. constraints that are applicable independently of the LSP class) should be allowed during P2MP TE LSP message processing. It has to be emphasized that path computation and management techniques shall be as close as possible than those being used for PSC P2P TE LSPs and P2MP TE LSPs. Finally, note that bi-directional TE LSPs are not applicable to multicast traffic. Although many leaf nodes may be considered as senders in a multicast group, a P2MP TE LSP models a single distribution tree from a sender to multiple recipients. If such a tree were made bi-directional it would be a multipoint-to-point tree in the reverse direction. 5.17 Requirements for Hierarchical P2MP TE LSPs [LSP-HIER] define concepts and procedures for P2P LSP hierarchy. They should be extended to support P2MP LSP hierarchy. The P2MP MPLS-TE solution SHOULD support the concept of region and region hierarchy (PSC1<PSC2<PSC3<PSC4<L2SC<TDM<LSC<FSC). Particularly it SHOULD allow a Region i P2MP TE LSP to be nested into a region j P2MP TE LSP or multiple region j P2P TE LSPs, providing that i<j. 5.18 P2MP Crankback routing P2MP solution SHOULD support cranckback requirements as defined in [CRANKBACK]. In particular, it SHOULD provide sufficient information to a branch LSR from downstream LSRs to allow the branch LSR to re-route a sub-tree around any failures or problems in the network. 6. Security Considerations This requirements draft does not define any protocol extensions and does not, therefore, make any changes to any security models. It should be noted that P2MP signaling mechanisms built on P2P signaling are likely to inherit all of the security techniques and problems associated with RSVP-TE. These problems may be exacerbated in P2MP situations where security relationships may need to maintained between an ingress and multiple egresses. Such issues are similar to security issues for IP multicast. It is a requirement that documents offering solutions for P2MP LSPs have detailed security sections. 7. Acknowledgements The authors would like to thank George Swallow, Ichiro Inoue and Dean Cheng for their review and suggestions on an earlier draft of this document. 8. References 8.1 Normative References [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. [RFC3031] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001. [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and W. Weiss, "An Architecture for Differentiated Services", RFC 2475, December 1998. [RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski, "Assured Forwarding PHB Group", RFC 2597, June 1999. [RFC3246] Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le Boudec, J.Y., Davari, S., Courtney, W., Firioiu, V. and D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop Behavior)", RFC 3246, March 2002. [RFC2362] D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering, M. Handley, V. Jacobson, C. Liu, P. Sharma, L. Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification.", RFC 2362, June 1998. [RFC2702] D. Awduche, J. Malcolm, J. Agogbua, M. O'Dell, J. McManus, "Requirements for Traffic Engineering Over MPLS", RFC2702, September 19991999. 8.2 Informational References [PIM-SM] B. Fenner, M. Hadley, H. Holbrook, I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM):Protocol Specification (Revised)", draft-ietf-pim-sm-v2-new-08.txt, October 2003. [BGP/MPLS IP VPNs] E. Rosen, Y.Rekhter, Editor, "BGP/MPLS IP VPNs", draft-ietf-l3vpn-rfc2547bis-01.txt, September 20032003. [RFC3471] Berger, L., Editor, "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC3473] Berger, L., Editor, "Generalized Multi-Protocol Label Switching (GMPLS) Signaling - Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. [RFC3477] K. Kompella, Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol -Traffic Engineering (RSVP-TE)", RFC3477, January 2003. [GMPLS-ROUTING] K. Kompella, Y. Rekhter, Editor, "Routing Extensions in Support of Generalized Multi-Protocol Label Switching", draft-ietf-ccamp-gmpls-routing-08.txt, October 2003. [STEINER] H. Salama, et al., "Evaluation of Multicast Routing Algorithm for Real-Time Communication on High-Speed Networks," IEEE Journal on Selected Area in Communications, pp.332-345, 19971997. [DJIKSTRA] E. W. Djikstra, "A note on two problem in connection with graphs," Numerische Mathematik, vol.1, pp.269-271, 19591959. [IPMCAST-MPLS] D. Ooms, B. Sales, W. Livens, A. Acharya, F. Griffoul and F. Ansari, "Overview of IP Multicast in a Multi-Protocol Label Switching (MPLS) Environment", RFC3353, August 2002. [FRR] P. Pan, D. Gan, G. Swallow, J. P. Vasseur, D. Cooper, A. Atlas, M. Jork,"Fast Reroute Extensions to RSVP-TE for LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-03.txt, July 20032003. [RFC3564] F. Le Faucheur, W. Lai, "Requirements for Support of Differentiated Services-aware MPLS Traffic Engineering", RFC3564, July 20032003. [OSPF-TE] D. Katz, D. Yeung, K. Kompella, "Traffic Engineering Extensions to OSPF Version 2", draft-katz-yeung-ospf-traffic-08.txt, September 20022002. [IS-IS-TE] Henk Smit, Tony Li, "IS-IS extensions for Traffic Engineering", draft-ietf-isis-traffic-04.txt, December 20022002. [CRANKBACK] A. Farrel, A. Satyanarayana, A. Iwata, N. Fujita, G. Ash S. Marshall, "Crankback Signaling Extensions for MPLS Signaling", draft-ietf-ccamp-crankback-00.txt, December 2003. [LSP-HIER] K. Kompella, Y. Rekhter, "LSP Hierarchy with Generalized MPLS TE", draft-ietf-mpls-lsp-hierarchy-08.txt, September 2002. [NODE-ID] Vasseur, Ali and Sivabalan, "Definition of an RRO node-id subobject", draft-ietf-mpls-nodeid-subobject-01.txt, June 2003. 9. Author's Addresses Seisho Yasukawa NTT Network Service Systems Laboratories, NTT Corporation 9-11, Midori-Cho 3-Chome Musashino-Shi, Tokyo 180-8585 Japan Phone: +81 422 59 4769 EMail:Email: email@example.com Dimitri Papadimitriou (Alcatel) Francis Wellensplein 1, B-2018 Antwerpen, Belgium Phone : +32 3 240 8491 EMail:Email: firstname.lastname@example.org JP Vasseur Cisco Systems, Inc. 300 Beaver Brook Road Boxborough ,Boxborough, MA -01719 USA Email: email@example.com Yuji Kamite NTT Communications Corporation Innovative IP Architecture Center,Tokyo Opera City Tower 21F, 20-2, 3-chome, Nishi-Shinjuku,3-20-2 Nishi Shinjuku, Shinjuku-ku, Tokyo,Tokyo 163-1421, Japan. EMail:Japan Email: firstname.lastname@example.org Rahul Aggarwal Juniper Networks 1194 North Mathilda Ave. Sunnyvale, CA 94089 Email: email@example.com Alan Kullberg Motorola Computer Group 120 Turnpike Rd. Southborough, MA 01772 Email: firstname.lastname@example.org Adrian Farrel Old Dog Consulting Phone: +44 (0) 1978 860944 EMail:Email: email@example.com Markus Jork Avici Systems 101 Billerica Avenue N. Billerica, MA 01862 email: firstname.lastname@example.org phone:Phone: +1 978 964 2142 Email: email@example.com Andrew G. Malis Tellabs 2730 Orchard Parkway San Jose, CA 95134 Phone: +1 408 383 7223 Email: firstname.lastname@example.org Jean-Louis Le Roux France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex France Email: email@example.com 10. 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