Article ID:5814
Introduction
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:
- Configure Virtual Local Area Network (VLAN) on the switch through the CLI. For instructions, click here.
- Enable Bridge Multicast Filtering through the CLI. For instructions, click here.
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. To learn how to configure MLD snooping settings on your switch through the CLI, click here.
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 Snooping Settings on a graphical user interface (GUI), click here.
Applicable Devices
- Sx350 Series
- SG350X Series
- Sx550X Series
Software Version
- 2.3.0.130
Configure IGMP Snooping
Configure Global IGMP Snooping
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: To learn how to access an SMB switch CLI through SSH or Telnet, click here.
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:
SG350X(config)#ip igmp snooping
Step 4. (Optional) To globally enable IGMP snooping querier, enter the following:
SG350X(config)#ip igmp snooping querier
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:
SG350X(config)#ip igmp snooping vlan [vlan-id]- 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:
SG350X(config)#ip igmp snooping vlan [vlan-id] mrouter learn pim-dvmrp
Step 3. (Optional) To enable the IGMP snooping Immediate Leave processing on a VLAN, enter the following:
SG350X(config)#ip igmp snooping vlan [vlan-id] immediate leave
Step 4. In the Global Configuration mode, enter the VLAN Interface Configuration context by entering the following:
SG350X(config)#interface [vlan-id]
Step 5. To configure the IGMP last member query counter, enter the following:
SG350X(config-if)#ip igmp last-member-query-count [count]- 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:
SG350X(config)#exit
Step 7. To enable the IGMP Snooping querier on a specific VLAN, enter the following:
SG350X(config)#ip igmp snooping vlan [vlan-id] querier
Step 8. To enable IGMP querier election mechanism of an IGMP snooping querier on a specific VLAN, enter the following:
SG350X(config)#ip igmp snooping vlan [vlan-id] querier election
Step 9. To configure the IGMP version of an IGMP Snooping querier on a specific VLAN, enter the following:
SG350X(config)#ip igmp snooping vlan [vlan-id] querier version [2 | 3]
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:
SG350X(config)#ip igmp snooping vlan [vlan-id] querier [ip-address]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:
SG350X(config)#exit
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:
SG350X#show ip igmp snooping interface [vlan-id]
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:
SG350X#copy running-config startup-config
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.