igmp robust-count
Function
The igmp robust-count command sets an IGMP querier robustness variable on an interface.
The undo igmp robust-count command restores the default IGMP querier robustness variable on an interface.
By default, the IGMP querier robustness variable is 2.
Parameters
| Parameter | Description | Value |
|---|---|---|
| robust-value | Specifies the IGMP querier robustness variable. It is the number of attempts to retransmit messages in case of packet loss on a congested network. | The value is an integer that ranges from 2 to 5. |
Usage Guidelines
Usage Scenario
On a shared network segment, a querier maintains IGMP-attached group memberships. The robustness variable affects the timeout interval of group memberships. The timeout interval of group memberships is calculated using the formula:
Timeout interval of group memberships = Interval for sending IGMP General Query messages x Robustness variable + Maximum response time
The robustness variable determines the following values:
Number of times the querier sends General Query messages when the querier starts
When a querier starts, it sends General Query messages certain times specified by the robustness variable to query the multicast groups that have members on the shared network segment. The message sending interval during this process is 1/4 of the query configured using the igmp timer query or timer query command.
Number of times the querier sends IGMPv2 Group-Specific Query messages or IGMPv3 Source/Group-Specific Query messages when the querier receives a Leave message
When receiving an IGMP Leave message of a multicast group, the querier sends Group-Specific Query messages certain times specified by the robustness variable to check whether the group has members. When the querier receives a Report message indicating that source-group mapping changes, the querier sends Source/Group-Specific Query messages certain times specified by the robustness variable. The interval for sending Group-Specific Query messages and Source/Group-Specific Query messages is set using the igmp lastmember-queryinterval or lastmember-queryinterval command.
Prerequisites
Multicast routing has been enabled using the multicast routing-enable command.
Precautions
The igmp robust-count command has the same function as the robust-count command used in the IGMP view. The configuration in the IGMP view is globally valid in the instance, whereas the configuration in the interface view is valid only for the current interface. The system prefers the configuration in the interface view. The configuration in the IGMP view is used only when the configuration in the interface view is not done.
