In a firewall sometimes we need to allow an IP through on a specific port, without whitelisting it. To do so:
Create your desired rule. For example, if we want to create a rule to allow inbound MySQL connections from IP 3.4.5.6 it would look like this:

In many situations, we might need to allow or deny an IP for a particular time period for doing maintenance or allow access to a specific port while it’s globally blocked. In such situations, it is the best way to temporarily allow/deny IP addresses in CSF.