38-2
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 38 Configuring IP Multicast
About IP Multicast
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:
•
IP Multicast Protocols, page 38-2
•
IP Multicast Implementation on the Catalyst 4500 Series Switch, page 38-4
•
Configuring IP Multicast Routing, page 38-13
IP Multicast Protocols
The Catalyst 4500 series switch primarily uses these protocols to implement IP multicast routing:
•
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.
Figure 38-1
IP Multicast Routing Protocols
Catalyst 4500 series switch
Router
Internet
PIM
IGMP and
IGMP
Snooping
Host A
Host B
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