MULTICAST IN MPLS ENVIRONMENT

Transcription

1 VIETNAM NATIONAL UNIVERSITY HOCHIMINH CITY HOCHIMINH CITY UNIVERSITY OF TECHNOLOGY P.F.I.E.V. THESIS SUMMARY MULTICAST IN MPLS ENVIRONMENT Students: QUỐC HƯNG VÕ P THANH THIỆN PHẠM NGUYỄN P THANH TUẤN PHẠM NGUYỄN P Instructor: M.E. TRÍ NGHĨA TẠ Hochiminh City, June 2005

2 Abstract Abstract Multicast and MPLS are two complementary technologies. Merging these two technologies where multicast trees are constructed over MPLS networks will enhance performance and present an efficient solution for bandwidth management. In this paper, we present a summary for the thesis IP Multicast in MPLS Environment. This paper is organized as follows. In first section, we present the statement of problem. Section 2, 3, 4 describes the objectives when we do research on multicast, MPLS and the merging of these two technologies. In section 5, we glance through the related work. The thesis structure and reference documents can be found in section 6 and 7. ii

3 Acknowledgments Acknowledgments The work on this thesis has been an inspiring, often exciting, sometimes challenging, but always interesting experience. It has been made possible by many other people, who have supported us. We are very grateful to our instructor Mr. Trí Nghĩa Tạ who has given us the chance to participate in several interesting research projects. He has supported us with his enthusiasm and many fruitful discussions. We wish to thank our families for their love, continuous support and encouragement. iii

4 Contents Contents 1. Statement of Problem Objectives IP Multicast MPLS IP Multicast in MPLS Related Work Thesis Structure...7 iv

5 Statement of Problem 1. Statement of Problem Several evolving applications like WWW, video/audio on-demand services, and teleconferencing consume a large amount of network bandwidth. Multicasting is a useful operation for supporting such applications [RFC3170]. Using the multicast services, data can be sent from a source to several destinations by sharing the link bandwidth. Besides, Multi-protocol label switching (MPLS) has emerged as an elegant solution to meet the bandwidth management and service requirements for next generation Internet protocol (IP) based backbone networks [RFC3031]. Working on these two topics separately at first time, we always try to answer a question, How can multicast be supported in MPLS environment? And we can find the answer in RFC Overview of IP Multicast in a Multi-Protocol Label Switching (MPLS) Environment [RFC3353] and numerous other resources in Internet. Although this topic is not totally new and the applications haven t been widely deployed yet but there s a lot of chances for development in the next-generation network where multimedia applications are dominant. In other words, supporting multicast in MPLS is a requirement, not an option. Based on the distribution of multicast groups, there are several multicast routing protocols appeared such as DVMRP, MOSPF, PIM-SM, PIM-DM, CBT, MBGP [Adams]. Among these protocols, PIM-SM (Protocol Independent Multicast Sparse Mode) is the most widely implemented protocol when deployed by Cisco, Juniper,... [Cisco M6]. It is a complicated protocol when building source-rooted shortest path trees, precluding the requirement of an RP and a shared tree [RFC2362]. In the context of the thesis, we will focus on the operation of PIM-SM protocol in MPLS environment. This project is a theoretical and simulational study of the implementation of the PIM-SM protocol in MPLS networks where the simulation tool used is the NS network simulator. In more details, before diving in MPLS techniques applied to PIM-SM protocol, in the thesis, we will get through IP Multicast and MPLS on theory and simulation. The objectives of each part will be deeply described as below. 2. Objectives 2.1. IP Multicast A number of emerging network applications require the delivery of packets from one or more senders to a group of receivers. These applications include bulk data transfer (for example, the transfer of a software upgrade from the software developer 1

6 Objectives to users needing the upgrade), streaming continuous media (for example, the transfer of the audio, video, and text of a live lecture to a set of distributed lecture participants), shared data applications (for example, a whiteboard or teleconferencing application), Web cache updating, and interactive gaming... For each of these applications, an extremely useful abstraction is the notion of a multicast: the sending of a packet from one sender to multiple receivers with a single send operation [Kurose-Ross]. Figure 2.1: Comparing Multicast and Unicast With this technique, a single datagram is transmitted from the sending host. This datagram (or a copy of this datagram) is then replicated at a network router whenever it must be forwarded on multiple outgoing links in order to reach the receivers (as illustrated in Figure 2.1). With these functional demands, a multicast routing protocol should be simple to implement, scalable, robust, use minimal network overhead, consume minimal memory resources, and inter-operate with other multicast routing protocols. Many multicast protocols have been proposed and are in use today on the Internet. They include (but not limited to) DVMRP, MOSPF, PIM-SM, PIM-DM, CBT, MBGP (see [Adams] for more details about these protocols). The differences between these protocols lies mainly in the type of multicast routing trees they build. DVMRP, MOSPF, and PIM-DM build multicast spanning trees that use shortest paths from every source to any destination. PIM-SM, CBT build spanning trees that are shortest path from a known central core, also called rendezvous point (RP), where all sources in the session share the same spanning tree. PIM-SM (Protocol Independent Multicast Sparse Mode) is the most widely implemented protocol so it will be deeply studied in this thesis. PIM-SM was designed 2

7 Objectives to operate efficiently across wide area networks, where groups are sparsely distributed. It uses the traditional IP multicast model of receiver-initiated membership, supports both shared and shortest-path trees, is not dependent on a specific unicast routing protocol, and uses soft-state mechanisms to adapt to changing network conditions [Microsoft PIM]. The simulation plays an important role in the study of scenes that are sometimes impossible to implement in practical platforms, or when we need to evaluate some alternative solutions without the necessity of implementing them. The Network Simulator 2 (NS-2) [NS] is the most popular simulator in the scientific field and in the telecommunications companies, allowing the creation of any network topology and analyze any kind of protocol. The NS supports some multicast protocols, as in example the PIM-DM, DVMRP and PIM-SM. Within the scope of IP multicast in this thesis, we will discuss general topics such as multicast group concept, IP multicast addresses. We also mention the overview of some intradomain multicast protocols, such as Internet Group Management Protocol (IGMP), Distance Vector Multicast Routing Protocol (DVMRP), Protocol Independent Multicast (PIM). Then, PIM-SM will be described in details for the purpose of studying PIM-SM in MPLS environment. At the end, we make the simulation to describe in visual manner the operation of different multicast protocols, comparing to unicast. The other simulations will evaluate the performance (through the figures and graphs) to compare and contrast the differences between unicast and multicast protocols. All of these simulations will clarify what we have just introduced about IP Multicast MPLS A data network is a set of nodes connected by links. The nodes are routers, LAN switches, WAN switches,... connected by links from 64 Kb DS0 circuits to OC192 and 10 gigabit Ethernet. One fundamental property of data networks is multiplexing. Two main types of multiplexing to be concerned are time-division multiplexing (TDM) and statistical multiplexing (statmux). A good example of TDM is the Synchronous Optical Network (SONET) hierarchy. However, the expense of TDM make statistical multiplexing technologies became more popular. Three major statmux technologies are IP, Frame Relay and ATM [Osborne]. When we replaced TDM circuits with Frame Relay and ATM circuits, it meant that IP would run over FR or ATM. This is generally suboptimal because mechanisms 3

8 Objectives of resource contention at one statmux often don't translate well into another. In this situation, we have two things desirable. Either we avoid congestion in Layer 2 statmux network, or find a way to map Layer 3 contention control mechanisms to Layer 2 contention control mechanisms. The former method is both impossible and financially unattractive. The latter one is feasible and is one of the reasons that makes MPLS (Multiprotocol Label Switching) is playing an important part in today's networks. Multiprotocol because it can be applied with any layer 3 network protocol, although almost interest is in using it with IP traffic [Osborne]. The MPLS (Multiprotocol Label Switching) architecture describes the mechanisms to perform label switching, which combines packet forwarding based on Layer 2 switching with Layer 3 routing. The concept of label is not new. A label in MPLS is similar to DLCI in Frame Relay or VPI/VCI (virtual path identifier/virtual channel identifier) in ATM. However, the way labels are assigned and the capability to carry a stack of labels in MPLS header enable new applications, such as Traffic Engineering, Virtual Private Networks, protection, and so on... [Guichard-Pepelnjak] MPLS have three main advantages. The first benefit of MPLS are decoupling routing and forwarding. Indeed, the concept of breaking Layer 3-based forwarding is not new. It is done before with IP policy-based routing but the configuration is so complex and less dynamic. The second, MPLS is supposed a bridge between IP and ATM. ATM switches dynamically assign VPI/VCI values that are used as labels for cells. This solution resolves the overlay-scaling problem without the need for centralized ATM-IP resolution servers which are bottlenecks of overlay model. The third, the most important benefit MPLS brings about, is basis for building nextgeneration network applications and services, such as MPLS VPN and MPLS TE [Osborne] In the context of the thesis IP Multicast in MPLS Environment, we mention mainly some MPLS basic concepts which greatly support us to understand how to deploy Multicast in MPLS. They are some crucial MPLS terms and definitions, MPLS forwardings basics, label creation and distribution over MPLS domain, signalling protocol LDP, CR-LDP Besides, we analyse a little about MPLS TE and use MPLS TE as a tool to help provide high-quality services. At the end, to clarify what we have just introduced about MPLS, we make a program simulating the roperation of MPLS. The small program is based on module MNS (MPLS Network Simulator) written by Gaeil Ahn and Woojik Chun, Department of Computer Engineering, Chungnam National University, Korea. 4

9 Objectives In the simulation program, we construct a topology which is contained MPLS nodes, transmitter and receiver nodes attaching with MPLS nodes. The transmitter sends data to receiver through LSP (Label Switched Path), if we want packet in MPLS domain take the shortest path to destination like IP packet in IP network, or ER-LSP (Explicit Route-Label Switch Path) when we want to route traffic along the path we want. In addition, a transmitter can send traffic of different classes which have various priority to the receiver through tunnels to illustrate the capability of QoS treatment of MPLS domain IP Multicast in MPLS One question to ask before looking in detail at MPLS multicast issues is, What are the potential benefits of MPLS to multicast routing? One possible answer to this is performance. Whereas the performance benefits of MPLS for unicast appear quite modest, the higher complexity of multicast forwarding (relative to unicast) might lead to a more significant performance advantage when label switching is used for multicast [Davie-Rekhter]. A second benefit of MPLS for multicast would be the ability to perform IP multicast on ATM-LSRs [Farinacci], thus removing the need for complex mappings from IP to ATM multicast. On contrast, what are the potential benefits when multicast supported in MPLS environment? The answer is easier, multicast reduces the traffic on all networks in which multicast is used, including MPLS network. Supporting multicast in current MPLS network is a requirement, not an option. Because of the benefits as described above, MPLS can be deployed in a network to forward unicast traffic through explicit routes and multicast traffic by using explicit trees. However the deployment of multicast in MPLS arises some difficulties because multicast traffic has specific characteristics due to the nature of the multicast routing protocols. Futhermore, while MPLS offers great flexibility in packet forwarding, it does not enrich the functionality of native IP multicast routing. So, in order to support Multicast in MPLS environment, we must map layer 3 multicast trees onto layer 2 LSPs by appropriate modifications in Multicast routing protocols and/or MPLS architecture as well. This mapping arises some problems in multipoint-to-multipoint LSP design, traffic aggregation, [Yang] A framework for IP multicast deployment in an MPLS environment is proposed in [RFC3353] and [Farinacci]. Issues arising when MPLS techniques are applied to IP multicast are overviewed. Following characteristics are considered: aggregation, flood and prune, co-existence of source and shared trees, uni/bidirectional shared trees, encapsulated multicast data, loop freeness and RPF check. The pros and cons of 5

10 Related Work existing IP multicast routing protocols in the context of MPLS are described and the relation to the different trigger methods and label distribution modes are discussed. However, in the context of the thesis, as mentioned at first, we will focus on the operation of PIM-SM protocol in MPLS. So, the characteristics which are directly relevant to this multicast routing protocol will be analysed in more detail. There are several ideas to deploy multicast in MPLS domain. Section Related Work below will list some of these. In these ideas, there is a appropriate approach for PIM-SM, that is Piggy-backing methodology. In piggy-backing, instead of sending 2 separate messages to construct L3 multicast trees and L2 LSPs, the label advertisement can be piggy-backed on the existing multicast routing messages. With PIM-SM, multicast routing message is the explicit Join/Prune messages [Farinacci]. In thesis, we will focus in great detail the rules of label distribution, Join/Prune packet modifications, and the pros and cons of piggy-backing. In the simulation section, we will have some modifications in MPLS Network Simulator source code to support PIM-SM source trees in MPLS. These modifications are originally proposed by [Boudani] based on Piggy-backing methodology. The idea is that in the branching routers, instead of mapping the <incoming Label, incoming Interface> to one <outgoing Label, outgoing Interface>, the mapping is done to several outgoing interfaces according to the distribution of the group members. When a data packet arrives, instead of doing only one label switching, the data packet is replicated, and for each copy a label switching is done. These copies are transmitted then to the convenient outgoing interfaces. In addition, before the transmission of data, label distribution is done from the downstream member up toward the source at the same time this member joins group. In other words, labeling is piggy-backed by multicast join-group message. The pruning is done also from the pruned member up toward the source. At each node a label deallocation is done until reaching either the source or a branching node. If it reaches a branching node, only the corresponding <outgoing interface, outgoing label> is removed and the branching node will probably become a tree node. This simulator can ef ciently help researchers to simulate and evaluate their MPLS multicast and multicasting related techniques. 3. Related Work A framework for MPLS multicast traf c engineering proposed by Ooms et al [RFC3353] gives an overview about the application of MPLS techniques to IP multicast. Another study about MPLS and multicast proposed by Farinacci et al [Farinacci] explains how to use PIM to distribute MPLS labels for multicast routes. A piggy-backing method is suggested to assign and distribute labels for multicast traf c 6

11 Thesis Structure for sparse-mode trees. Based on this methodology, Boudani et al [Boudani] build a multicast routing simulator over MPLS network. All the these are the main references of the thesis. Another study of [Acharya] suggests a solution for the co-existence of source and shared tree problem. This proposal can be also applied to PIM-DM. In this approach, one assigns source specific labels on the nodes of the shared tree. Multiple labels will be associated with one shared tree state, corresponding to one label per active source. Since the nodes only know which sources are active when traffic from these sources arrives, the LSPs cannot be pre-established and a fast LSP setup method is favorable. Another proposal is aggregated multicast [Fei]. The key idea of aggregated multicast is that, instead of constructing a tree for each individual multicast session in the core network, one can have multiple multicast sessions sharing a single aggregated tree to reduce multicast state and, correspondingly, tree maintenance overhead at network core. A new approach to construct multicast trees in MPLS networks [Boudani-MMT] was proposed recently. In that approach, MPLS LSPs are used between multicast tree branching node routers in order to reduce forwarding states and enhance scalability. Only routers that are acting as multicast tree branching nodes for a group need to keep forwarding states for that group. All other non-branching node routers simply forward data packets over traf c engineered unicast routes using MPLS LSPs. 4. Thesis Structure Chapter 1: Introduction Chapter 2: IP Multicast Theory Chapter 3: MPLS Theory Chapter 4: PIM-SM in MPLS Chapter 5: IP Multicast Simulation Chapter 6: MPLS Simulation Chapter 7: PIM-SM in MPLS Simulation 7

12 References References [Acharya] Arup Acharya et al, IP Multicast Support in MPLS Networks, Internet Draft, February 1999, pp 6-7. [Adams] Brian Adams, Ed Cheng, Tina Fox, Andy Kessler, Mark Manzanares, Bryan Mclaughlin, Jim Rushton, Beverly Tai, Kevin Tran, Interdomain Multicast Solutions Guide, (ebook version), Cisco Press, July 2002, chapter 1. [Ahn-Chun] G. Ahn and W. Chun, Architecture of MPLS network simulator (MNS) for the setup of CR-LDP, ower.ce.cnu.ac.kr/fog1/mns, [Almaroth] K. Almaroth, The Evolution of Multicast: From the MBone to Interdomain Multicast to Internet2 Deployment, In IEEE Network, January [Altman] Eitan Altman and Tania Jiménez, NS Simulator for beginners, Lecture notes [Boudani] Ali Boudani et al, Multicast Routing Simulator over MPLS Networks, Technical report 1493, IRISA, October [Camilo] Tiago Camilo, Jorge Sá Silva, and Fernando Boavida, Enabling NS-2 With SSM Environments, Coimbra University. [Cisco Intro] Introduction to IP Multicast, Powerpoint Presentation, Cisco Systems. [Cisco29220] Multicast Support for MPLS VPNs Configuration Example, Document ID: 29220, Cisco Systems. [CiscoMPVN] Multicast VPN Data Sheet, Cisco Systems. [Davie-Rekhter] Bruce S. Davie, Yakov Rekhter, MPLS: Technology and Applications, Morgan Kaufmann, 1st edition (May 19, 2000), chapter 5, pp [Farinacci] Dino Farinacci et al, Using PIM to Distribute MPLS Labels for Multicast Routes, Internet Draft, November [Gallagher] Rick Gallaher, Rick Gallagher's MPLS Training Guide: Building Multi- Protocol Label Switching Networks, Syngress Publishing. [Guichard-Pepelnjak] Jim Guichart and Ivan Pepelnjak, MPLS and VPN architectures, volume I, part I (ebook version), Cisco Press. [Hakimi] S.L. Hakimi, Steiner's problem in graphs and its implications, Networks, vol. 1, pp , [Hardwick] Jon Hardwick, IP Multicast Explained, white paper, Data Connection Ltd., June [Kurose-Ross] J. Kurose and K. Ross, Computer Networking: A Top Down Approach Featuring the Internet, Addison Wesley, 2nd ed, chapter 4. [Microsoft PIM] PIM-SM Multicast Routing Protocol, White Paper, Microsoft. [ns Manual] Kevin Fall, Kannan Varadhan, The ns Manual, The VINT Project, April 8

13 References 11, [NS] The Network Simulator - ns-2, June [Osborne] Eric Osborne and Ajay Simha, Traffic Engineering with MPLS, Cisco Press, Chapter 1-7. [PIM] Deering, S., Estrin, D., Farinacci, D., Jacobson, V., Liu, C., Wei, L., Sharma, P., and A. Helmy, Protocol Independent Multicast (pim): Motivation and Architecture, Work in Progress. [RFC1075] D. Waitzman, S. Deering, C. Partridge, Distance Vector Multicast Routing Protocol, RFC 1075, Nov [RFC2003] C. Perkins, IP Encapsulation within IP RFC 2003, Oct [RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering, S., Handley, M., Jacobson, V., Liu, C., Sharma,. and L. Wei, Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification, RFC 2362, June [RFC3031] E. Rosen, A. Viswanathan, R. Callon, Multiprotocol Label Switching Architecture, RFC 3031, January 2001, pp [RFC3032] E. Rosen, D. Tappan, G. Fedorkow et al, MPLS Label Stack Encoding, RFC 3032, January [RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and R. Thomas, LDP Specification, RFC 3036, January 2001, pp [RFC3170] B. Quinn, K. Almeroth, IP Multicast Applications: Challenges and Solutions, RFC 3170, September [RFC3212] Jamoussi, B., Andersson, L., Callon, R., Dantu, R., Wu, L., Doolan, P., Worster, T., Feldman, N., Fredette, A., Girish, M., Gray, E., Heinanen, J., Kilty, T. and A. Malis, Constraint-based LSP Setup Using LDP, RFC 3212, January 2002, pp [RFC3353] D. Ooms, B. Sales, W. Livens, A. Acharya, F. Griffoul, F. Ansari, Overview of IP Multicast in a Multi-Protocol Label Switching (MPLS) Environment, RFC 3353, August [RFC3973] A. Adams, J. Nicholas, W. Siadak, Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol Specification (Revised), RFC 3973, January [Rosen] E. Rosen, Multicast in MPLS/BGP IP VPNs, Internet Draft, December [Trilium] Multiprotocol Label Switching (MPLS), Trilium, [Wei] L. Wei and D. Estrin, A comparison of multicast trees and algorithms, TR USC- CD , Dept. Computer Science, University of California, Sept [Yang] Baijian Yang, Prasant Mohapatra, Edge Router Multicasting with MPLS Traffic Engineering,