Chapter 8. Multicasts

Terms you'll need to understand:

• Unicast, broadcast, and multicast

• Internet Group Management Protocol (IGMP)

• Source-based and shared distribution trees

• Protocol Independent Multicast (PIM) routing protocol

• IGMP snooping

• Cisco Group Management Protocol (CGMP)

Techniques you'll need to master:

• Using multicast addresses

• Knowing the similarities and differences between IGMPv1, v2, and v3

• Knowing the differences between PIM sparse and dense modes

• Configuring and verifying PIM

The bulk of communications in campus networks today involve unicast traffic. Because of the deployment of video applications in a campus network, as well as broader use of multicast applications on the Internet, bandwidth on campus networks is becoming saturated. Those campus network video applications might include desktop video conferencing, LAN TV and radio, and collaborative computing. A multicast, like a unicast, is both a Layer 2 and Layer 3 process. However, with a multicast, a group of machines can be the destination of the traffic, whereas a unicast has only one destination.

As an example, consider a LAN-based TV multicast application that generates 1Mbps of traffic from the server. By default, this traffic must be dispersed to every segment that has a participating multicast client. Because of the increased use of these applications, it is critical to understand traffic and bandwidth characteristics when designing a scalable network that won't affect every end station.