After the masking rule is created and active UP/DOWN alarms are still received.
I observed that even if the masking rule is active this applies only to alarms received from the devices via SNMP. However you you want to stop receiveing UP/DOWN alarms you should first disable the device polling feature and then activate the masking rule.
The means for obtaining UP/DOWN alarms from devices in the monitored network should be analyzied. One is through SNMP and for using this way you should configure SNMP on the devices. The other way a built-in eSIght mechanism called device polling. Device polling uses ICMP messages to poll device status at a set time interval.
This feature is new (available only on V200R003C00SPC300) and has not been included in official documentation so please pay attention to the system setting page of eSight if you encouter this problem.