Intel, Microsoft, Cisco Systems, and children's favorite Toys-R-Us are all companies that have deployed cost-saving and business-enabling multicast solutions. These are just companies with large enterprise networks and even ISPs are activating multicast on their production networks. Multicast is a unique aspect of routing in networks that has been steadily growing in use across the Internet. However, many engineers have yet to acknowledge its growing role. Certainly your everyday Internet consumer is completely oblivious to its existence as an overlay on the Internet known as the multicast backbone ( mbone ). In a typical IPv4 unicast routing scenario, delivery, ordering, and delay are not guaranteed . Although multicast employs techniques to use bandwidth more efficiently , there is still no guarantee of delay and ordering. Thus, in addition to multicast techniques, proper application deployment and internal application correction methods need to be implemented to take advantage of multicast fully. Do not misunderstand ”multicast does have some issues associated with it, the largest being that network engineers do not seem to believe in it as a solution, it has no built-in network congestion avoidance mechanism, there are packet duplication issues, and because multicast commonly uses UDP as the transport mechanism, packet delivery can be unreliable at times. As multimedia in all its forms more strongly dominates the realm of networking in general and the Internet in particular, the use of multicast becomes ever more important. Juniper Networks has a strong multicast implementation that enables the issues associated with multicast to be better addressed through the support of many of the newer multicast protocols designed to cope with these issues. Mbone was at its inception like many fundamental stalwarts of the Internet today ”an experiment. The IETF wanted to broadcast its meetings to those unable to be present who were located across the globe. The idea at the time was to create a volunteer-based experiment to explore how to successfully transmit audio and video from one source to many destinations. The technology to provide this type of host and network capabilities evolved into several new technologies known collectively as multicasting. Mbone is an interconnected set of subnetworks of routers that support multicast. These routers are grouped together into multicast islands that are then overlaid onto the Internet as shown in Figure 14-2. An island is connected to another island over the Internet via a tunnel (a virtual point-to-point link). These tunnels allow multicast traffic to pass undisturbed through the portions of the Internet that are not multicast-enabled. Figure 14-2. Multicast Islands in Mbone Architecture
The deployment and continued growth of mbone is important to multicast and its use, as well as its evolution. However, the need, or more specifically , the commercial and business factors involved in driving growth in multicast is even more important. In conclusion mbone is winding down, and the experiment is over. The experiment was extremely successful and demonstrated that multicast and tunneling could be accomplished. Today and in the future, we will see many large ISPs, including Sprint, Level3, and WorldCom, continue to incorporate multicast into their production networks. These networks, in general, are using PIM as their multicast protocol of choice, instead of DVMRP, through either MBGP or MSDP. Later, this chapter will introduce and discuss these protocols. The standards relating to multicast are as follows :
To access Internet RFCs and drafts, go to the IETF Web site at www.ietf.org. These standards are current in their status at the time of this writing. It is always good to look beyond the standards to how they have been interpreted. The following additional resources can assist:
14.1.1 Benefits of MulticastingBefore this chapter delves into the details of how multicasting works, the following list describes some of the benefits of multicasting. We will look at these benefits first from a network engineer's perspective and then from a cost-profit business perspective.
Events in the arenas of both Internet politics and personal Internet use are also contributing to the continued growth of multicast. Consider the following more specific snapshot of factors and business or personal uses for multicast:
As the Internet has evolved and information sharing has increased, many different models to share information via the Internet have been developed. Some have gotten the rest of the world really stirred up, but the point here is that multicasting applications are on the rise and this will continue! Are you ready? 14.1.2 JUNOS Multicast ImplementationsMulticast routing is the key to multicast and is the framework upon which multicast packets are routed to recipients. Some of the concepts that we will introduce here will be explained in other sections, but it is good to get comfortable with the proper multicast terminology at the outset. JUNOS implements the following protocols to support IP multicast routing:
It is commonly understandood that when discussing multicast and BGP, the "m" in MBGP stands for "multicast," even though the RFC defines it as "multiprotocol." |