(Optional) Configuring an IGMP Snooping Querier
Context
When IGMP snooping is enabled on a Layer 2 device, the Layer 2 device can listen on IGMP protocol packets exchanged between an IGMP querier and user hosts to dynamically create Layer 2 multicast forwarding entries and provide Layer 2 multicast functions.
A Layer 2 device cannot create Layer 2 multicast forwarding entries by listening on IGMP protocol packets in the following conditions, even when IGMP snooping is enabled on the device:
The interfaces on the upstream Layer 3 multicast device have static multicast groups configured and do not run the IGMP protocol.
The multicast source is located on the same Layer 2 network as user hosts, and therefore no Layer 3 multicast device is required.
In either of the preceding conditions, you can configure the IGMP snooping querier on the Layer 2 multicast device. Then the Layer 2 multicast device substitutes for a Layer 3 multicast device to send IGMP Query messages to user hosts.
Procedure
- Run system-view
The system view is displayed.
- Run vlan vlan-id
The VLAN view is displayed.
- Run igmp-snooping querier enable
The IGMP snooping querier function is enabled.
The IGMP snooping querier function cannot be enabled in a VLAN if the corresponding Layer 3 VLANIF interface has Layer 3 multicast functions (such as IGMP and PIM) enabled.
After an IGMP snooping querier is enabled, the router periodically broadcasts IGMP Query messages to all the interfaces in a VLAN, including the router ports in the VLAN. This may result in IGMP querier reelection if an IGMP querier already exists on the multicast network. If an IGMP querier already exists on the multicast network, configuring IGMP snooping querier is not recommended. If you configure an IGMP snooping querier on a switch, ensure that the source IP address of the General Query messages sent from the switch is larger than the IP address of the upstream IGMP querier.
- (Optional) Set the querier parameters.
When setting the querier parameters, ensure that the interval for sending IGMP General Query messages is larger than the maximum response time for IGMP Query messages.
Querier Parameter
Configuration Command
Description
Default Setting
Version
Interval for sending IGMP General Query messages
igmp-snooping query-interval query-interval
The querier sends IGMP General Query messages at the specified interval to maintain memberships of interfaces in a VLAN.
60 seconds IGMPv1, IGMPv2, and IGMPv3
IGMP robustness variable
igmp-snooping robust-count robust-count
The robustness variable defines the following values:- Number of times the querier sends General Query messages after startup. The packet sending interval is 1/4 of the configured interval for sending General Query messages.
- Number of times the querier sends Group-Specific Query messages after receiving a Leave message. The packet sending interval is the same as the configured interval for sending Group-Specific Query messages.
2
IGMPv1, IGMPv2, and IGMPv3
Maximum response time for IGMP Query messages
igmp-snooping max-response-time max-response-time
When receiving IGMP Report messages from hosts, the router sets the aging time of member ports by using the following formula: Aging time = IGMP robustness variable x Interval for sending IGMP General Query messages + Maximum response time.
After a multicast member receives an IGMP Query message, it must send a Report message within the maximum response time.
10 seconds
IGMPv2 and IGMPv3
Interval for sending IGMP Group-Specific Query messages
igmp-snooping lastmember-queryinterval lastmember-queryinterval
When receiving IGMP Leave messages from a host, the router calculates the aging time of the member port by using the following formula: Aging time = Interval for sending Group-Specific Query messages x IGMP robustness variable. The router sends a Group-Specific Query message certain times (specified by the IGMP robustness variable) to check whether this group has any other members.
1 second
IGMPv2 and IGMPv3
- (Optional) Run quit
Return to the system view.
- (Optional) Run igmp-snooping send-query source-address ip-address
The source IP address of an IGMP General Query message is configured.
By default, the source IP address of an IGMP General Query message sent by the IGMP snooping querier is 192.168.0.1. If this IP address is used by other devices on the network, you can use this command to set another IP address.
