Chapter 35 Configuring Ip Multicast - Cisco Catalyst 4500 Series Configuration Manual

About IP Multicast
to the destination host by routers. At each point on the path between source and destination, a router uses
a unicast routing table to make unicast forwarding decisions, based on the IP destination address in the
packet.
At the other end of the IP communication spectrum is an IP broadcast, where a source host sends packets
to all hosts on a network segment. The destination address of an IP broadcast packet has the host portion
of the destination IP address set to all ones and the network portion set to the address of the subnet. IP
hosts, including routers, understand that packets, which contain an IP broadcast address as the
destination address, are addressed to all IP hosts on the subnet. Unless specifically configured otherwise,
routers do not forward IP broadcast packets, so IP broadcast communication is normally limited to a
local subnet.
IP multicasting falls between IP unicast and IP broadcast communication. IP multicast communication
enables a host to send IP packets to a group of hosts anywhere within the IP network. To send
information to a specific group, IP multicast communication uses a special form of IP destination
address called an IP multicast group address. The IP multicast group address is specified in the IP
destination address field of the packet.
To multicast IP information, Layer 3 switches and routers must forward an incoming IP packet to all
output interfaces that lead to members of the IP multicast group. In the multicasting process on the
Catalyst 4500 series switch, a packet is replicated in the Integrated Switching Engine, forwarded to the
appropriate output interfaces, and sent to each member of the multicast group.
We tend to think of IP multicasting and video conferencing as the same thing. Although the first
application in a network to use IP multicast is often video conferencing, video is only one of many IP
multicast applications that can add value to a company's business model. Other IP multicast applications
that have potential for improving productivity include multimedia conferencing, data replication,
real-time data multicasts, and simulation applications.
This section contains the following subsections:
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IP Multicast Protocols
The Catalyst 4500 series switch primarily uses these protocols to implement IP multicast routing:
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Figure 35-1
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
35-2
IP Multicast Protocols, page 35-2
IP Multicast Implementation on the Catalyst 4500 Series Switch, page 35-4
Restrictions on Using Bidirectional PIM, page 35-12
Internet Group Management Protocol (IGMP)
Protocol Independent Multicast (PIM)
IGMP snooping and Cisco Group Management Protocol
shows where these protocols operate within the IP multicast environment.
Chapter 35 Configuring IP Multicast
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