Select a device implementing IPMROUTE-STD-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 ipMRouteNextHopClosestMemberHops under the ipMRouteNextHopEntry branch of IPMROUTE-STD-MIB, selecting the specific row/instance you want to monitor since this is a table column, then select it and click OK. It reports the minimum number of hops between this router and the nearest member of a given IP multicast group, reached via a specific next-hop. 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 an Integer32-type OID, Value bounds is the most useful condition here — trigger an alert if the hop count grows well beyond its normal baseline for that group, which can indicate a multicast routing topology problem. Click Finish to create the monitor; you can adjust any parameter later.