1.2.a [iv] Adding multicast support
Traditional IP communication allows a host to send packets to a single host (unicast transmission) or to all hosts (broadcast transmission). IP multicast provides a third scheme, allowing a host to send packets to a group of hosts. These hosts are known as group members. Packets delivered to group members are identified by a single multicast group address . Multicast packets are delivered to a group using best-effort with UDP transport, just like IP/ UDP unicast packets. The multicast environment consists of senders and receivers. Any host, regardless of whether it is a member of a group or not, can send to a group. However, only the members of a group receive the data.
A multicast address is chosen for the receivers in a multicast group. Senders use that address as the destination address of a datagram to reach all members of the group. Membership in a multicast group is dynamic; hosts can join and leave at any time. There is no restriction on the location or number of members in a multicast group, and a host can be a member of more than one multicast group at a time. The Cisco IOS supports the following protocols to implement IP multicast routing:
● IGMP is used between hosts on a LAN and the routers on that LAN to track the multicast groups of which hosts are other members.
● Protocol Independent Multicast (PIM) is used between routers so that they can track which multicast packets to forward to each other and to their directly connected LANs.
● Distance Vector Multicast Routing Protocol (DVMRP) is used on the MBONE (the multicast backbone of the Internet). The Cisco IOS software supports PIM-to-DVMRP interaction.
● Cisco Group Management Protocol (CGMP) is used on routers connected to Catalyst switches to perform tasks similar to those performed by IGMP.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1268-1275). . Kindle Edition.