buildroot

config BR2_PACKAGE_KNOCK

    bool "knock"

    select BR2_PACKAGE_LIBPCAP

    depends on BR2_USE_MMU # fork()

    help

      A port knocking implementation.

      Provides a daemon and a user application. Port knocking can be

      used to run an arbitrary application, once the daemon detects

      a predefined sequence of incoming TCP/UDP packets on a network

      interface. This can be used, e.g. to open up ports in a

      firewall.

​

      http://www.zeroflux.org/projects/knock