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122 Chapter 6 Using Multicast Manager
208963-B
Multicast protocols
Passport 1000 Series switches and Passport 8600 switches support the following
multicast protocols:
• Distance Vector Multicast Routing Protocol (DVMRP)
• Internet Group Management Protocol (IGMP)
• IGMP Snooping
At its most basic, IP multicast is the communication of data and services to
multiple destinations with a single transmission. Refer to Networking Concepts
for the Passport 1000 Series Routing Switch Release 2.0 and Networking
Concepts for the Passport 8000 Series Routing Switch for more information on
multicast and multicast protocols.
DVMRP
DVMRP advertises shortest-path routes to multicasting source networks (any
network containing hosts with the capability to issue multicast datagrams). When
DVMRP is coupled with IGMP membership, a multicast stream is learned from
both the routers and directly attached hosts.
IGMP
IGMP allows a host to register group memberships with the local querier router to
receive any datagrams sent to this router and targeted to a group with a specific IP
Multicast address. The protocol also allows a router to learn the existence of
group members on its directly attached networks. The router periodically sends a
general query message to each of its local networks. Any host that is a member of
any multicasting group identifies itself by a sending a response.
IGMP Snooping
IGMP Snooping uses IGMP messages to prune group membership per port within
a VLAN. The switch listens to group reports for each port and builds a database of
multicast group members per port. Only those ports that are specified in the
database receive multicast traffic, instead of all the ports in the VLAN.