This section describes the syntax for creating filters, how to create and delete filters, how to manage filters in your firewall configuration, and the differences between traditional IP filters and firewall filters. Each filter has a name assigned to it.
File names are case-insensitive.
When a new filter is created with the same name as an existing filter, the new filter replaces the old one, in memory and on the disk. A filter must have at least one rule defined within it. A filter begins with the left parenthesis, and terminates with the right parenthesis. In between the parenthesis, any number of rules are allowed. Empty rules are ignored.