Understanding and Configuring Multicast Operation

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 helps you understand the differences in unicast, broadcast, and multicast communication
methods and when each should be used. Unicast is an excellent method of point-topoint
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 learn 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 (found on the accompanying CD), 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.