Web Manager for Administrators > Configuration>Network>Firewall Configuration > Firewall Configuration: Inverted Checkboxes

Firewall Configuration: Inverted Checkboxes
If the “Inverted” checkbox is checked on any line in the “Add Rule” or “Edit Rule” dialog boxes under Configuration>Network>Firewall Configuration in Expert mode, the target action is performed on packets that do not match any of the criteria specified in that line when any other specified criteria are also met.
For example, if you select DROP as the target action, check “Inverted” on the line with a source IP address specified, and do not specify any other criteria in the rule, any packets arriving from any other source IP address than the one specified are dropped.

Web Manager for Administrators > Configuration>Network>Firewall Configuration > Firewall Configuration: Inverted Checkboxes