Chapter 8: Understanding and Configuring Multicast Operation

The CCNP Exam Topics Covered in This Chapter Include the Following:

• Describe the functionality of CGMP

• Describe how switches facilitate Multicast Traffic

• Translate Multicast Addresses into MAC addresses

• Enable CGMP on the distribution layer devices

• Describe how IP multicast operates on a multilayer switched network, including IGMP versions 1, 2, and 3 and CGMP

• Understand how IP multicast operates on a routed network, including PIM in both sparse and dense modes

Today's web and enterprise applications are directed to larger audiences on the network than ever before, causing increased bandwidth requirements. This increased demand on bandwidth can be accommodated with as little cost increase as possible by using multicast. For example, voice and video are being sourced for larger and larger audiences and one-on-one communications can overwhelm both servers and network resources. Unlike unicast and broadcast, however, multicast services can eliminate these problems.

This chapter will help you understand the differences in unicast, broadcast, and multicast communication methods and when each should be used. Unicast is an excellent method of point-to-point communication, whereas broadcast traffic is imperative for many systems and protocols to work on a network. Multicast comes in as a bridge between these two communication extremes by efficiently allowing point-to-multipoint data forwarding. It is essential that you understand how multicast addressing spans both layer 3 and layer 2 of the OSI model. You will also learn about the protocols and tools used to implement and control multicast traffic on your network. As with any service that runs on your network, you must understand the resources needed and the potential implications of enabling multicast forwarding.

You will also cover the steps and syntax for configuring IP multicast on Cisco routers and switches. You will see several new commands in this chapter. By the time you finish this chapter, and its review questions and lab, you will be thoroughly familiar with multicast and its implementation. Pay attention to small details that might usually seem unimportant. They are often the key to a successful implementation of an IP multicast network.

You will learn how to deploy an IP multicast network, and after you have a plan in place, you will move on to configuring equipment. Not only do the routers have to be IP multicast enabled, but you must enable a multicast protocol on every interface through which you want to be able to forward multicast traffic.

An IP multicast network can result in traffic flows that are very hard to predict. One way of preventing this problem is to try and force traffic along specific paths, and using specified routers as Rendezvous Points (RPs) to assist in this process is quite common, so you have to configure them as well. Then, to keep your multicast local to the enterprise network, you need to configure the Time to Live (TTL) thresholds on your external interfaces.

After the routers have been configured, you can concentrate on the hosts. Of course, we won't discuss host configuration in this chapter, but we will enable Cisco Group Management Protocol (CGMP) on the routers and switches, so that after the hosts are configured, the network will be available.