Multimedia Traffic Control with IP Multicast (IGMP)

More on IGMP Operation

IGMP is NOT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 3 is

 

 

 

 

 

 

 

 

 

 

Switch 1

 

 

 

 

 

 

 

running on

 

 

 

 

 

 

 

 

 

 

 

Server

 

 

running IGMP

 

switches 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

and operating

 

and 2.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

as the querier.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Multicast

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Data Stream

 

 

Switch 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PC 2

 

 

 

 

 

 

 

 

 

 

 

 

IGMP IS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

running on

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

switch 4.

 

PC 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PC 5

PC 6

Figure 12-4. Isolating IP Multicast Traffic in a Network

In the above figure, the multicast group traffic does not go to switch 1 and beyond because either the port on switch 3 that connects to switch 1 has been configured as blocked (through IGMP or another means) or there are no hosts connected to switch 1 or switch 2 that belong to the multicast group.

For PC 1 to become a member of the same multicast group without flooding IP multicast traffic on all ports of switches 1 and 2, IGMP must be configured on both switches 1 and 2, and the port on Switch 3 that connects to Switch 1 must be unblocked. (Blocking can be due to the current IGMP configuration or to another reason unrelated to IGMP.)

Data-Driven IGMP

An IP multicast packet includes the multicast group (address) to which the packet belongs. When an IGMP client connected to a switch port needs to receive multicast traffic from a specific group, it joins the group by sending an IGMP report (join request) through the switch to the network. (The multicast group specified in the join request is determined by the requesting application running on the IGMP client.) When a networking device with IGMP enabled receives the join request for a specific group, it forwards any IP

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