Hello Ram
IGMPv3 uses two filter modes that provide a lot more flexibility and granularity in managing multicast traffic compared to previous versions. These modes are INCLUDE and EXCLUDE. These are not explicitly configured on a Cisco device but are part of the operation of the IGMPv3 protocol itself. They are used to determine how a host receiver wants to receive multicast traffic from various sources.
According to RFC 3376, the filter mode is further described as follows:
"filter-mode" may be either INCLUDE or EXCLUDE. In INCLUDE mode, reception of packets sent to the specified multicast address is requested *only* from those IP source addresses listed in the source-list parameter. In EXCLUDE mode, reception of packets sent to the given multicast address is requested from all IP source addresses *except* those listed in the source-list parameter.
In the lesson, you see an example of how the INCLUDE mode is used. Again, it’s not explicitly configured, however, it is inferred by the IGMP protocol based on the configuration. Under what circumstances would we see an EXCLUDE mode? Here is an example:
Router(config)# interface gigabitethernet0/0
Router(config-if)# ip igmp join-group 239.1.1.1 source 192.168.1.1
In this situation, the router is acting as a multicast host that is requesting to join the 239.1.1.1 multicast group. By configuring the source of the multicast traffic, it is essentially excluding the addresses stated in the source list. In the above case, that is the 192.168.1.1 address. Based on the above description from the RFC, this should give us an EXCLUDE mode in the IGMPv3 message.
I hope this has been helpful!
Laz