Summary

Multicast forwarding is relatively new. Until the growth of applications that required multicast delivery, it was used by service protocols such as 'all OSPF routers'. Now, many multimedia applications-such as video-and wide distribution applications-such as market data feeds- all require multicast delivery.

We have therefore given a lot of time to understanding the many facets of IP multicast. We started with an overview of multicast and compared it to unicast and broadcast communication, and then discussed how IP addresses were designated as multicast addresses. These layer 3 addresses must be converted to layer 2 MAC addresses using a standard mapping process.

Of course, theoretical knowledge needs to be backed up with an understanding of how to configure multicast on both Cisco routers and switches, because the routers carry the multicast traffic over the internetwork and the switches deliver it to the multicast hosts. The syntax of the commands is straightforward, but you need to ensure that the network is properly planned before starting the implementation. Care needs to be taken when considering the IGMP version to be used, for example.

When considering the multicast distribution, you need to select between PIM-DM, PIM-SM, and CBT. All three are independent protocols that use tree distribution to manage multicast data delivery in a network, but all affect the network operation in different ways, and require different configurations.