anchor.diff:        default = false;
         description =
           ''
  -          Whether to enable the firewall.
  +          Whether to enable the firewall.  This is a simple stateful
  +          firewall that blocks connection attempts to unauthorised TCP
  +          or UDP ports on this machine.  It does not affect packet
  +          forwarding.
           '';
       };
     
  
positive.code:                 ''
                    ip46tables -A INPUT -p tcp --dport ${toString port} -j ACCEPT
                  ''
                ) config.networking.firewall.allowedTCPPorts
              }
  
              # Accept packets on the allowed UDP ports.
  
negative.code: 
          preStart =
            ''
              # Helper command to manipulate both the IPv4 and IPv6 tables.
              ip46tables() {
                iptables "$@"
                ip6tables "$@"
  