Select a device implementing IGMP-MIB as the target host to create a monitor — the SNMP service should be up and running on it. Click New Monitor, then check SNMP Custom on the Favorites tab, click Next, and confirm the host. On the next page, click Select... to open the built-in SNMP MIB Browser and locate igmpCacheUpTime under the igmpCacheEntry branch of IGMP-MIB, selecting the specific row/instance you want to monitor since this is a table column, then select it and click OK. It reports, in TimeTicks, how long the system has been a member of this IGMP multicast group — a value of 0 means it is not currently a member. On the monitor's Main parameters page you can set the target's SNMP port (default 161), credentials, polling interval, and other settings — see the SNMP Monitor help for details. On the State conditions and Alerting tabs, configure when the monitor should change state and trigger an alert; since this is a TimeTicks-type OID, Value bounds is the most useful condition here — trigger an alert if the value unexpectedly drops to 0 for a group your applications rely on, indicating group membership was lost. Click Finish to create the monitor; you can adjust any parameter later.