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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
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Chapter 44 Configuring IP Multicast Routing
Understanding Cisco’s Implementation of IP Multicast Routing
• Internet Group Management Protocol (IGMP) is used among hosts on a LAN and the routers (and
multilayer switches) on that LAN to track the multicast groups of which hosts are members.
• Protocol-Independent Multicast (PIM) protocol is used among routers and multilayer switches to
track which multicast packets to forward to each other and to their directly connected LANs.
• Distance Vector Multicast Routing Protocol (DVMRP) is used on the multicast backbone of the
Internet (MBONE). The software supports PIM-to-DVMRP interaction.
• Cisco Group Management Protocol (CGMP) is used on Cisco routers and multilayer switches
connected to Layer 2 Catalyst switches to perform tasks similar to those performed by IGMP.
Figure 44-1 shows where these protocols operate within the IP multicast environment.
Figure 44-1 IP Multicast Routing Protocols
According to IPv4 multicast standards, the MAC destination multicast address begins with 0100:5e and
is appended by the last 23 bits of the IP address. For example, if the IP destination address is 239.1.1.39,
the MAC destination address is 0100:5e01:0127.
A multicast packet is unmatched when the destination IPv4 address does not match the destination MAC
address. The switch forwards the unmatched packet in hardware based the MAC address table. If the
destination MAC address is not in the MAC address table, the switch floods the packet to the all port in
the same VLAN as the receiving port.
This section includes information about these topics:
• Understanding IGMP, page 44-2
• Understanding PIM, page 44-3
• Understanding DVMRP, page 44-8
• Understanding CGMP, page 44-9
Understanding IGMP
To participate in IP multicasting, multicast hosts, routers, and multilayer switches must have the IGMP
operating. This protocol defines the querier and host roles:
Host
Host
PIM
IGMP
CGMP
DVMRP
Internet
MBONE
Cisco Catalyst switch
(CGMP client)
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