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.
This article provides instructions on how to configure the IGMP settings on your switch, through the Command Line Interface (CLI). If you prefer to configure IGMP or MLD Snooping Settings using a graphical user interface (GUI), click here.
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.
Step 2. From the Privileged EXEC mode of the switch, enter the Global Configuration mode by entering configure.
Step 3. To globally enable IGMP snooping on the switch, entering 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.
Configure IGMP Snooping Settings on a VLAN
Step 1. To enable IGMP snooping on a specific VLAN, enter the following:
- vlan-id — Specifies the VLAN ID value. The range is from one up to 4094.
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:
- count — The number of times that group or group-source-specific queries are sent upon receipt of a message indicating a leave. The range is from one to seven.
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:
Note: In this example, version 3 is used.
Step 10. To define the source IP address that the IGMP snooping querier uses, enter the following:
Note: If an IP address is configured for the VLAN, it is used as the source address of the IGMP snooping querier. If there are multiple IP addresses, the minimum IP address defined on the VLAN is used.
Note: In this example, 192.168.100.112 is used. If an IP address is not configured by this command, and no IP address is configured for the VLAN of the querier, the querier is disabled.
Step 11. Enter the exit command to go back to the Privileged EXEC mode:
You should now have successfully configured the IGMP snooping settings on your switch through the CLI.
Display IGMP Snooping Settings on a VLAN
Step 1. To display the IGMP snooping configuration for a specific VLAN, enter the following:
Note: In this example, the IGMP snooping settings for VLAN 30 are displayed.
Step 2. (Optional) In the Privileged EXEC mode of the switch, save the configured settings to the startup configuration file by entering the following:
Step 3. (Optional) Press Y for Yes or N for No on your keyboard once the Overwrite file [startup-config]... prompt appears.
You should now have displayed the IGMP settings on a VLAN on your switch through the CLI.