Example: Modifying the MLD Robustness Variable

This example shows how to configure and verify the MLD robustness variable in a multicast domain.

Requirements

Before you begin:

Configure the router interfaces. See the Network Interfaces Configuration Guide.
Configure an interior gateway protocol or static routing. See the Routing Protocols Configuration Guide.
Enable IPv6 unicast routing. See the Routing Protocols Configuration Guide.
Enable PIM. See PIM Background.

Overview

The MLD robustness variable provides fine-tuning to allow for expected packet loss on a subnet. Increasing the robust count allows for more packet loss but increases the leave latency of the subnetwork.

The value of the robustness variable is used in calculating the following MLD 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. The number can be from 2 through 10. You might want to increase this value if you expect a subnet to lose packets.

Configuration

CLI Quick Configuration

To quickly configure the MLD robustness variable, copy the following command and paste it into the CLI.

[edit]set protocols mld robust-count 5

Step-by-Step Procedure

To change the value of the robustness variable:

Configure the robust count.
[edit]user@host# edit protocols mld[edit protocols mld]user@host# set robust-count 5
If you are done configuring the device, commit the configuration.
[edit protocols mld]user@host# commit

Verification

To verify the configuration is working properly, check the MLD Robustness Count field in the output of the show mld interfaces command.