Modifying the IGMP Robustness Variable
The IGMP robustness variable provides fine-tuning to allow for expected packet loss on a subnet. The value of the robustness variable is used in calculating the following IGMP message intervals:
- Group member interval—Amount of time that must pass before a multicast router decides that there are no more members of a group on a network. This interval is calculated as follows: (robustness variable x query-interval) + (1 x query-response-interval).
- Other querier present interval—Amount of time that must pass before a multicast router decides that there is no longer another multicast router that is the querier. This interval is calculated as follows: (robustness variable x query-interval) + (0.5 x query-response-interval).
- Last-member query count—Number of group-specific queries sent before the router assumes there are no local members of a group. The default number is the value of the robustness variable.
By default, the robustness variable is set to 2. You might want to increase this value if you expect a subnet to lose packets. To change the value of the robustness variable, include the robust-count statement:
robust-count number;
You can include this statement at the following hierarchy levels:
- [edit protocols igmp]
- [edit logical-systems logical-system-name protocols igmp]
The number can be from 2 through 10.
