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Deploying IP Multicast in the Enterprise

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Deploying IP Multicast in the Enterprise


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  • Copyright 1998
  • Dimensions: 7" x 9-1/4"
  • Pages: 304
  • Edition: 1st
  • Book
  • ISBN-10: 0-13-897687-2
  • ISBN-13: 978-0-13-897687-3


IP Multicast: Get ready for the future of Enterprise broadcasting!

With multicasting, it's possible to send data, video, and audio to many requesting clients simultaneously, across the Internet or any other IP-based network. Multicasting is an essential building block for a new generation of applications, such as leading-edge "push" applications (including news and sports updates, real-time stock quotes, and others),software distribution, and certain multimedia applications.

In this book, Thomas A. Maufer-co-author of the "Introduction to IP Multicast Routing" Request for Comments (RFC)-closely examines the protocols which make multicasting possible - and the challenging routing issues that arise in enterprise Multicasting. Maufer explains the rationale for multicast, describes important classes of multicast-enabled applications, and the essentials of multicast IP technology, including the "host group" model and the Internet Group Management Protocol (IGMP).

Ensure successful deployment of a multicast infrastructure over your existing networks by understanding how multicast routing protocols work.Protocols such as the Distance Vector Multicast Routing Protocol, Multicast Extensions to OSPF, Protocol-Independent Multicast - Dense Mode are discussed, along with the exciting new Protocol-Independent Multicast - Sparse Mode, and Core Based Trees protocols.

Multicast-based transport protocols are discussed, including the Realtime Transport Protocol (RTP), and so-called "reliable" multicast transport protocols are examined. Finally, watch IP Multicast at work in two leading-edge deployments: Networld+Interop's InteropNet, and NASA's Jet Propulsion Laboratory.

Understand IP Multicast now -- and deploy it tomorrow.

  • Practical deployment considerations for enterprise intranets
  • Current and future intranet multicast routing protocols
  • Current and emerging applications: Conferencing, whiteboards, news updates, live or pre-recorded media streaming events, software distribution, reliable multicast transport protocols, the Service Location Protocol, etc.
  • Multicast routing interoperability frameworks, "reliable" multicast transport protocols, the Realtime Transport Protocol, and more
  • The history and possible future evolution of the Internet's Mbone
  • For all network engineers and managers developing multicast-enabled applications for use on the Internet or intranet

Sample Content

Table of Contents



1. Introduction.

What is an Intranet? How Is an Intranet Different? Understanding the Need for Multicast. Broadcast. Replicated Unicast. Network-Layer Multicast.

2. IP Addressing Overview.

The IP Address Space. Unicast. 'Classes' of Network Numbers. Overview. What Is CIDR? Broadcast. Limited Broadcast. All-Subnets Broadcast. Subnet-Specific Broadcast. Anycast. Multicast. Reserved Multicast Addresses. Multicast Address Space. Multicast IP over IEEE 802 LANs. Multicast Summary.

3. Characteristics of Multicast Applications.

Identifying Multicast Applications. Multicast ­ Multimedia. Multicast Applications Are Not Necessarily Bandwidth-Intensive! Multidestination Applications Don't Always Use Multicast. Motivation for Multicast. Multicast Videoconferencing and Your Travel Budget. The Future of Multicast on Your Intranet. The History of IP on Your Intranet. Multicast Is Not Perfect (Yet) . . .


4. Multicast IP Fundamentals.

The Lineage of Multicast Standardization. “Host Group” Model. Controlling the Scope of Multicast Forwarding. Implicit Scoping. TTL-Based Scoping. Administrative Scoping.

5. Overview of the Internet Group.

Management Protocol. IGMP Version 1. IGMPv1 Protocol Overview. The IGMP Report Supression Technique. Detecting Group Membership Changes. End Stations and “Join Latency”. IGMP Version 2. IGMPv2 Querier Election. IGMPv2 New Messages. “Leave Latency” and IGMPv2. IGMPv2 Summary. IGMPv2 and IGMPv1 Coexistence Rules. Rules for IGMPv2 End Stations. Rules for Routers. IGMP Version 3 (Future).

6. Introduction to Multicast Routing and Forwarding.

Multicast Address Allocation. How Are Class D Addresses Assigned? Brief Overview of Routing Techniques. Broadcast and Prune. Examples of Broadcast-and-Prune Multicast Routing Protocols. Shared Trees. Multicast Forwarding versus Multicast Routing. Unicast versus Multicast Forwarding. Multicast Forwarding Procedure. Multicast Routing Protocols: Scalability and Routing Policy Issues.


7. Evolution of Reverse-Path Multicasting (RPM).

Flooding. Reverse-Path Broadcasting (RPB). Reverse-Path Broadcasting: Operation. RPB: Benefits and Limitations. Truncated RPB (TRPB). Reverse-Path Multicasting. Operation. Grafting. RPM's Limitations.

8. Distance-Vector Multicast Routing Protocol.

Physical and Tunnel Interfaces. Basic Operation. DVMRP Router Functions. DVMRP Routing Table. DVMRP Forwarding Table. DVMRP Tree Building and Forwarding Summary. Weaknesses in DVMRP. Deploying DVMRP. “Native” DVMRP Intranet. Backbone between Domains Running Other Multicast Routing Protocols. Connecting to the Internet's Multicast Backbone.

9. Protocol-Independent Multicast—Dense Mode.

Protocol-Independent Multicast Overview. PIM—Dense Mode (PIM-DM) PIM-DM Tree Building and Forwarding Summary.

10. Multicast Extensions to OSPF (MOSPF).

Intra-Area Routing with MOSPF. Local Group Database. Datagram's Shortest Path Tree. Forwarding Cache. Interarea Routing with MOSPF. Interarea Multicast Forwarders. An Interarea Datagram's Shortest Path Tree. Inter-Autonomous-System Multicasting with MOSPF. MOSPF Tree Building and Forwarding Summary. Weaknesses of MOSPF. Deploying MOSPF. Mixing MOSPF and OSPF Routers within an OSPF Routing Domain.


11. Core-Based Trees (CBT).

Intra-domain Bootstrapping. Joining a Group's Shared Tree. CBT Tree Maintenance. CBT's Designated Router. Data Packet Forwarding. CBT's Forwarding Cache. Non-Member Sending. CBT Tree Building and Forwarding Summary.

12. Protocol-Independent Multicast—Sparse Mode (PIM-SM).

PIM-SM Bootstrap Mechanisms. A Directly Attached Host Joins a Group. Directly Attached Source Sends to a Group. Shared Tree (RP-Tree) or Shortest Path Tree? PIM-SM Tree Building and Forwarding Summary.


13. Today: “MBone”.

MBone Defined. Experimental Overlay. Which Routing Protocol Is Used? MBone Applications. MBone Application Traits. MBone Myth—Not Limited to 512 kbps.

14. Tomorrow: Who Knows?

What's the Goal?. Multicast-Enabled Internet!!. Implication: Eliminate the M-BGP?. Mbone. BGMP/GUM?.


15. Multicast Routing Interoperability Frameworks.

Requirements for Multicast Border Routers. An Interoperability Hack: “Proxy IGMP”.

16. Expanding-Ring Searches and Service Location.

Issues with Expanding-Ring Searches Expanding-Ring Searches over Explicit-Join Protocol Regions. Service Location Protocol. How Are Directory Agents Discovered?. Details of SLP. SLP Scalability.

17. Introduction to “Reliable” Multicast Transport.

Protocols. What Is Reliability? Points of Reference. Reliable Unicast Transport (Transmission Control Protocol). Multicast Option for TFTP. Reliable Multicast—Expectations. Requirements for Multicast Reliable Transport Protocol(s). Example 1: Non-Mission-Critical Multicast Stock Ticker. Example 2: Video with Layered (Hierarchical) Coding. One Other Technique. Why Not Just Run TCP Over Multicast? A Partial Fix: Single Connection Emulation.

18. Some Reliable Multicast Transport Protocols.

Some Current Research Projects in Reliable Multicast. Scalable Reliable Multicast. Reliable Multicast Transport Protocol. Reliable Multicast Protocol (RMP). Reliable Adaptive Multicast Protocol (RAMP). Commercial Reliable Multicast Offerings. GlobalCast's Offerings. TIB from TIBCO. StarBurst's MFTP.

19. The Realtime Transport Protocol and Reliability.

Overview of RTP. Overview of RTCP. RTP-Based Reliable Multicast Transport Protocols. Lightweight Reliable Multicast Protocol. Parnes' RTP Extensions to Support SRM.


20. Networld+Interop's “InteropNet”.

What Is the InteropNet?. How Is the InteropNet Used?. Overview of the InteropNet's Design through the Years. Evolution of Multicast Usage on the InteropNet. Early. Later. Multicast Routing Alternatives for the Future InteropNet. Growth of Multicast Traffic.

21. Multicast IP at NASA's Jet Propulsion Laboratory.

Experimentaton with Multicast Technology. Experimentation and Technology Evaluation. Radio Free vat. Making It Real. Objectives of the Project. Prerequisites for Multicast Deployment. Network Architecture. Future Possibilities.


A. Glossary.
B. IGMP Details.

IGMPv2 Packet Formats. IP Options and the Router Alert Option. The Host Membership Report. The Two Query Messages. The Leave Group Message. IGMPv1 Packet Formats.

C. History of the MBone and Multimedia Conferencing.
D. High-Level Summary of Multicast Routing Protocols.
E. Multicast Standardization.

IETF. IEEE 802.1 Committee.

F. References.

IETF Requests for Comments (RFCs). IETF Internet Drafts. Textbooks. Other.




In the summer of 1995, my company (3Com Corporation) was preparing to ship multicast routing capabilities in one of its router products. At the time, I was part of a team that was responsible for helping our sales force and customers understand this technology and its importance, which often involved writing informational white papers and presentations about the technology with Chuck Semeria. By the end of 1995, we had a paper that introduced people to how multicast routing protocols worked.

After the IETF meeting in Dallas that December, we were encouraged by some fellow Internet Engineering Task Force (IETF) members to publish this document as an IETF informational Request for Comments (RFC). Because multicast routing concepts are unfamiliar to many people, an introductory document was viewed as an important companion to the standards being produced within the IETF.

Over the next 18 months, some of the multicast routing protocols evolved considerably in their predicted operating environments, standardization track, and even some of their internal features and mechanisms. The routing protocols had advanced beyond our original paper, so consequently we wished to delay publishing the RFC until the specifications had stabilized—after all, we didn't want the “Introduction to IP Multicast Routing” to be based on outdated information. Once the majority of these protocols had been finalized, or nearly finalized (circa early 1997), we rewrote the document to reflect the “final” details of the protocols. Just as the protocols had changed during their initial development and standardization phase, it is inevitable that they will continue to evolve over time; in addition, new protocols will be invented. While the document is really only accurate once, it is unlikely that the fundamental concepts will change, and we hope that the RFC will still be useful in the years to come.

Based on an earlier internet-draft version of this developing RFC, Prentice Hall approached us regarding building a book around the foundation laid by the RFC. Given the increasing interest in multicast technology, it seemed like the time was right for such a book. The book introduces the reader to the core ideas of this subject matter, so that they may understand the mechanisms employed, enabling educated decisions on which protocols to deploy in their own unique networks, and allowing them to envision how multicast routing may affect their individual enterprise intranetworks.

Beyond the details provided on the multicast routing protocols, multicast applications are discussed, and also topics which are the subject of active research and intense interest, such as reliable multicast transport protocols. The book concludes with two case studies of existing networks that are already using multicast routing, exploring deployment issues and lessons learned. No two networks are alike, but hopefully the examples chosen will provide interesting reading for those planning to deploy multicast in their own intranets.

A solid multicast routing infrastructure is the key foundation upon which next- generation multicast applications are layered. Applications such as multimedia conferencing, “push-” oriented applications, multipoint data distribution, distance learning, etc., all depend on an efficient multipoint delivery service. Multicast is the key network infrastructure component enabling these and other next-generation applications.

This book is written for anyone that wants to learn about technologies related to multicast IP. It can serve as a quick reference book, giving the broad outlines of the various protocols. Enough details are provided that a reader should be able to understand the internal mechanisms employed by each protocol. Not all protocols are equally applicable to every networking scenario, so understanding how each different multicast routing protocol works is critical to the successful deployment of multicast routing. Knowing the benefits and limitations of each protocol enables network managers to make better-informed decisions about which protocol(s) are appropriate for use in their own networks.

Readers ought to have a basic operational understanding of unicast IP routing. While a basic introduction to unicast routing and addressing is included, it is not intended to be comprehensive, rather a refresher for concepts that are important to the explanation of multicast IP. Also helpful would be a good understanding of the basics of unicast IP applications, especially knowing how they employ the services of the unicast transport layer protocols.

At a minimum, this book will give readers a solid understanding of multicast routing protocols, and the sorts of existing applications that can make use of multicast. In addition, the book can serve as an introduction to more advanced applications enabled by multicast routing technology, including reliable multicast applications. Issues surrounding the use of multicast IP over the Internet are also explored. The case studies serve as proof points that multicast can be used in production networks, and shows what sorts of applications are of interest in these environments.


This book is not necessarily designed to be read from cover to cover, though a determined reader is welcome to try. Each chapter is designed to be fairly independent of the others, so that it may be used as a concise reference.

The book begins with a overview of the concepts of IP-based “intranets” and moves on to discuss multicast applications, along with a description of the motivation for multicast. Successive chapters place multicast IP in the context of unicast IP, and introduce concepts such as Classless Inter-Domain Routing (CIDR) and subnetting (including Variable-Length Subnet Masking (VLSM)). Before diving in to detailed descriptions of the various different multicast routing protocols, there is a discussion of how to identify and classify multicast applications, leading into a history of the standardization of multicast IP. Multicast “scoping” is discussed, then versions one and two of the Internet Group Management Protocol (IGMP) are explained. IGMP is the protocol that end stations must use to participate in multicast IP sessions.

The routers use information derived from IGMP to help build “trees” so that sources can send traffic to a group without knowing the exact group membership in advance. How the routers determine the shape of these trees is the essence of multicast routing, and all the major algorithms are covered in at least one chapter each. Each protocol takes a different approach to solving this problem, and each chapter includes a short summary of the protocol's tree building techniques and the methods employed to decide how to forward a multicast packet. Once all the existing multicast routing protocols have been covered, there is a discussion of a possible interoperability framework for these protocols, and two fundamental multicast techniques are discussed: expanding-ring searches and the Service Location Protocol.

From this foundation, we move on to introduce the concepts behind reliable multicast transport protocols. A full discussion of this very interesting topic could easily fill a book of its own. I have tried to distill the issues related to reliable multicast transport protocols so that the concepts involved in various techniques can be understood. As I said, a full discussion of the interactions of reliable multicast transport protocols and their associated applications, along with issues surrounding interactions with unicast transport protocols, is beyond the scope of this book. Many of these issues are not yet well understood, and still the subject of active research and debate. The main body of the book concludes with two case studies: InteropNet and NASA's Jet Propulsion Laboratory's campus network.

Finally, the book closes with five Appendices: a Glossary; a detailed discussion of IGMP, including details of all its packet formats; and a history of the development of multicast technology, including the Internet's multicast backbone (MBone). There is a high-level overview of the various multicast routing protocols, and an overview of the two main standards bodies doing work relevant to multicast IP. The book concludes with a list of references, including Requests for Comments (RFCs), some current IETF internet-draft documents, textbooks, and other documents (e.g., Ph.D. theses).


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