Multimedia Traffic Control with IP Multicast (IGMP)

More on IGMP Operation

multicast traffic it receives for that group through the port on which the join request was received. To reduce unnecessary traffic, the networking device does not forward a given group’s multicast packets to ports from which a join request for that group has not been received. (If the switch or router has not received any join requests for a given multicast group, it drops the traffic it receives for that group.)

Video

Server

Outbound Multicast Traffic from Video Server for Group “A” on VLAN 3

 

 

 

 

 

 

Join Request

 

Series 5300XL Switch

 

 

for group “A”

 

 

 

Forward

 

 

 

 

 

from Host A1

 

 

 

 

 

Drop

 

on VLAN 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

No Join Request from Host A2 on VLAN 3

Host “A1”

Group “A” Multicast

Traffic for Host “A1”

Host “A2”

 

 

 

No Group “A” Multicast

 

 

Traffic for Host “A2”

 

 

 

Figure 12-5. Example of Data-Driven IGMP Operation

Thus, after you enable IGMP on a VLAN configured in the switch, it continually listens for IGMP messages and IP multicast traffic on all ports in the VLAN, and forwards IGMP traffic for a given multicast address only through the port(s) on that VLAN where an IGMP report (join request) for that address was received from an IGMP client device.

N o t e

IP multicast traffic groups are identified by IP addresses in the range of 224.0.0.0 to 239.255.255.255.

Incoming IGMP packets intended for reserved, or “well-known” multicast addresses automatically flood through all ports (except the port on which the packets entered the switch). For more on this topic, see “Excluding Well- Known or Reserved Multicast Addresses from IP Multicast Filtering” on page 12-21.

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