robust-count (IGMP)

Function

The robust-count command sets a global robustness variable for an IGMP querier.

The undo robust-count command restores the default robustness variable.

By default, the robustness variable of an IGMP querier is 2.

Format

robust-count robust-value

undo robust-count

Parameters

Parameter	Description	Value
robust-value	Specifies the robustness variable of an IGMP querier.	The value is an integer that ranges from 2 to 5.

Views

IGMP view of the public network instance, IGMP view of a VPN instance

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

The IGMP querier robustness variable specifies the retransmission count of IGMP packets to minimize the impact of packet loss on the network.

On a shared network, a querier maintains IGMP-attached group memberships on an interface. The robustness variable determines the timeout interval of group memberships. The timeout interval of group memberships is calculated using the following 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 at startup

When the querier starts, it sends General Query messages a certain number of times specified by the robustness variable to query members of multicast groups. The interval for sending General Query messages during this process is 1/4 of the interval configured using the igmp timer query or timer query command.
In IGMPv2 and IGMPv3, the robustness variable determines the number of times the querier sends Group-Specific Query or Source-and-Group-Specific Query messages.

When receiving an IGMP Leave message of a multicast group, the querier sends Group-Specific Query messages a certain number of 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-and-Group-Specific Query messages a certain number of times specified by the robustness variable. The interval for sending Group-Specific Query messages and Source-and-Group-Specific Query messages can be set using the igmp lastmember-queryinterval or lastmember-queryinterval command.

Prerequisites

IP multicast routing has been enabled using the multicast routing-enable command.

Precautions

A larger robustness variable makes an IGMP querier more robust, but increases the timeout interval of group memberships.
This command has the same function as the igmp robust-count command used in the interface view. The configuration in the IGMP view is globally valid, whereas the configuration in the interface view is valid only for the current interface. The configuration in the interface view takes precedence over the configuration in the IGMP view. The configuration in the IGMP view is used only when no configuration is performed in the interface view.

Example

# In the IGMP view, set the robustness variable of an IGMP querier to 3.

<HUAWEI> system-view
[HUAWEI] multicast routing-enable
[HUAWEI] igmp
[HUAWEI-igmp] robust-count 3