Portknocking with ferm example

ferm.conf

domain (ip) {
    table filter {

        #
        # Subchains: Portknocking
        # ################################################################################
        chain PORT_KNOCKING_1 {
            protocol tcp {
              mod recent name "port_knock_seq_01" set NOP;
            }
            DROP;
        }

        chain PORT_KNOCKING_2 {
            protocol tcp {
              mod recent name "port_knock_seq_01" remove NOP;
              mod recent name "port_knock_seq_02" set NOP;
            }
            DROP;
        }

        chain PORT_KNOCKING_3 {
            protocol tcp {
              mod recent name "port_knock_seq_02" remove NOP;
              mod recent name "port_knock_seq_03" set NOP;
            }
            DROP;
        }
        ################################################################################

        chain INPUT {
            policy DROP;

            proto tcp {
                
                #
                # Port knocking stuff
                ################################################################################
                dport 10000 {  mod recent    set name "port_knock_seq_01"             jump PORT_KNOCKING_1; }
                dport 20000 {  mod recent rcheck name "port_knock_seq_01" seconds 10  jump PORT_KNOCKING_2; }
                dport 30000 {  mod recent rcheck name "port_knock_seq_02" seconds 10  jump PORT_KNOCKING_3; }
                ################################################################################

                # allow SSH connections
                dport ssh {
                    mod recent rcheck name "port_knock_seq_03" seconds 120 ACCEPT; # open for ip with right port knocking sequence
                    DROP;
                }
                
                DROP;
            }
        }

        chain OUTPUT {
          ...
        }

        chain FORWARD {
          ...
        }
    }
} # domain