
Multicasting and Multimedia Overview
117355-A Rev. A
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Multicast Addresses
Each host group is assigned a unique multicast address. To reach all members of
the group, a sender uses the multicast address as the destination address of the
datagram.
An IP Version 4 multicast address is a Class D address (the high-order bits are set
to 1110) from 224.0.0.0 to 239.255.255.255.
The block of addresses from 224.0.0.1 to 224.0.0.255 is reserved for routing
protocols and other low-level protocols. Multicast routers will not forward
datagrams with addresses in this range.
Internet Group Management Protocol
The Internet Group Management Protocol (IGMP) has the following
characteristics:
• Allows a host to register group memberships with the local queries router to
receive any datagrams sent to this router and targeted to a group with a
specific IP multicast address.
• Allows a router to learn the existence of group members on its directly
attached networks. The router periodically sends a general group query
message to each of its local networks. Any host that is a member of a
multicasting group identifies itself by sending a response.
IGMP is described in Cha
pter 3.
Distance Vector Multicast Routing Protocol
DVMRP is a distance vector type of multicast routing protocol. It advertises
shortest-path routes to multicasting
source networks
-- that is, any network
containing hosts that have the capability to issue multicast datagrams. (In this
respect, DVMRP is the opposite of RIP, which advertises routes to destination
networks.)
DVMRP is described in Cha
pter 4.
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