122 Chapter 6 Using Multicast Manager208963-BMulticast protocolsPassport 1000 Series switches and Passport 8600 switches support the followingmulticast protocols:• Distance Vector Multicast Routing Protocol (DVMRP)• Internet Group Management Protocol (IGMP)• IGMP SnoopingAt its most basic, IP multicast is the communication of data and services tomultiple destinations with a single transmission. Refer to Networking Conceptsfor the Passport 1000 Series Routing Switch Release 2.0 and NetworkingConcepts for the Passport 8000 Series Routing Switch for more information onmulticast and multicast protocols.DVMRPDVMRP advertises shortest-path routes to multicasting source networks (anynetwork containing hosts with the capability to issue multicast datagrams). WhenDVMRP is coupled with IGMP membership, a multicast stream is learned fromboth the routers and directly attached hosts.IGMPIGMP allows a host to register group memberships with the local querier router toreceive any datagrams sent to this router and targeted to a group with a specific IPMulticast address. The protocol also allows a router to learn the existence ofgroup members on its directly attached networks. The router periodically sends ageneral query message to each of its local networks. Any host that is a member ofany multicasting group identifies itself by a sending a response.IGMP SnoopingIGMP Snooping uses IGMP messages to prune group membership per port withina VLAN. The switch listens to group reports for each port and builds a database ofmulticast group members per port. Only those ports that are specified in thedatabase receive multicast traffic, instead of all the ports in the VLAN.
