Chapter 42 Configuring IP Multicast Routing

Understanding Cisco’s Implementation of IP Multicast Routing

Understanding Cisco’s Implementation of IP Multicast Routing

The Cisco IOS software supports these protocols to implement 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 42-1shows where these protocols operate within the IP multicast environment.

Figure 42-1 IP Multicast Routing Protocols

Cisco Catalyst switch

(CGMP client)

CGMP

Host

PIM

Host

IGMP

Internet

MBONE

DVMRP

44966

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 42-3

Understanding PIM, page 42-4

Understanding DVMRP, page 42-8

Understanding CGMP, page 42-9

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

42-2

OL-9775-02

 

 

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Cisco Systems 3750E manual 42-2, IP Multicast Routing Protocols