Some Catalyst switches can be configured to intercept IGMP join requests as hosts ask to join IP multicast groups.
IGMP join requests can occur as the following happen:
- Hosts send unsolicited membership reports to join specific multicast groups.
- Multicast routers acting as IGMP queriers send IGMP membership query messages to the all-hosts multicast group 220.127.116.11 every 60 seconds. Interested hosts respond with membership reports to join specific multicast groups.
The switch keeps a record of the IP multicast group, its Layer 2 MAC address, and the switch ports that connect to the requesting host and the multicast router.
Multicast routers cannot keep a detailed list of all hosts belonging to a multicast group. Rather, a router ...