Select a Cisco MDS 9718 Multilayer Director 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 fcNameServerNumRows under the fcNameServerConfiguration branch of CISCO-NS-MIB, then select it and click OK. It reports the number of Fibre Channel Nx_Ports currently registered with this switch's name server, fabric-wide. 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 count drops well below its normal baseline, which would indicate hosts or storage ports have unexpectedly logged out of the fabric. Click Finish to create the monitor; you can adjust any parameter later.