Multicast is a technology created to conserve bandwidth. It is typically used to transmit data packets from one host to multiple hosts. To allow routers to distribute multicasts out one of its ports, they use a protocol called Internet Group Management Protocol (IGMP). Hosts send an IGMP join message to get a multicast stream. When a router receives an IGMP join message at one of its interfaces, it knows there are hosts interested in joining a multicast stream and sends it out. In early switches, multicast traffic was forwarded on all ports, even if only one host needs to receive it. IGMP snooping was developed to limit multicast traffic to only the requesting host or hosts.

When IGMP snooping is enabled, the switch detects the IGMP messages exchanged between the IPv4 router and the multicast hosts attached to the interfaces. It then maintains a table that forwards IPv4 multicast traffic to the ports that need to receive them.

The following configurations are prerequisites for configuring IGMP:

1. Configure VLAN Interface Settings on a Sx350, SG350X, or Sx550X Switch.

2. Configure Multicast Properties on a Switch.

Note: Multicast Listener Discovery (MLD) performs a similar function to IGMP, but for IPv6. If you purchased a switch that supports IPv6 and your infrastructure supports IPv6 multicast, then you can configure MLD. This is independent of IGMP snooping.

Sx350 Series

SG350X Series

Sx550X Series

2.3.0.130

Step 1. Log in to the switch console. The default username and password is cisco/cisco. If you have configured a new username or password, enter the credentials instead.

Note: The commands may vary depending on the exact model of your switch. In this example, the SG350X switch is accessed through Telnet.

Step 2. From the Privileged EXEC mode of the switch, enter the Global Configuration mode by entering the following:

Step 3. To globally enable IGMP snooping on the switch, enter the following:

Step 4. (Optional) To globally enable IGMP snooping querier, enter the following:

You should now have successfully configured the global IGMP snooping settings on your switch.

Step 1. To enable IGMP snooping on a specific VLAN, enter the following:

Note: In this scenario, the IGMP snooping settings for VLAN 30 are being configured.

Step 2. (Optional) To allow the multicast router to automatically learn the connected ports, enter the following:

Step 3. (Optional) To enable the IGMP snooping Immediate Leave processing on a VLAN, enter the following:

Step 4. In the Global Configuration mode, enter the VLAN Interface Configuration context by entering the following:

Step 5. To configure the IGMP last member query counter, enter the following:

Note: In this example, the last member query counter is set to 3.

Step 6. Enter the exit command to go back to the Global Configuration mode:

Step 7. To enable the IGMP Snooping querier on a specific VLAN, enter the following:

Step 8. To enable IGMP querier election mechanism of an IGMP snooping querier on a specific VLAN, enter the following:

Step 9. To configure the IGMP version of an IGMP Snooping querier on a specific VLAN, enter the following:

Step 10. To define the source IP address that the IGMP snooping querier uses, enter the following:

Step 11. Enter the exit command to go back to the Privileged EXEC mode:

Step 1. To display the IGMP snooping configuration for a specific VLAN, enter the following:

Step 2. (Optional) In the Privileged EXEC mode of the switch, save the configured settings to the startup configuration file by entering the following: