knock - port-knock client

       Judd Vinet <jvinet@zeroflux.org>

knockd 0.8                                       April 22, 2021                                        knockd(1)

knock  is  a  port-knock  client.   It  sends  TCP/UDP packets to each specified port on host, creating a
       special knock sequence on the listening server (see the knockd manpage for more info on this).

       knock myserver.example.com 123:tcp 456:udp 789:tcp
       knock -u myserver.example.com 8284 4721 18592 42912

       knock - port-knock client

-u,--udp
              Make all port hits use UDP (default is TCP).  If you want each port to use  a  different  protocol
              (TCP or UDP), then you can specify the protocol on a per-port basis.  See the example below.

       -d<t>,--delay<t>
              Wait  <t>  milliseconds  between  each  port  hit.   This can be used in situations where a router
              mistakes your stream of SYN packets as a port scan and blocks them.  If the packet rate is  slowed
              with --delay, then the router should let the packets through.

       -4,--ipv4<version>
              Force usage of IPv4.

       -6,--ipv6<version>
              Force usage of IPv6.

       -v,--verbose
              Output verbose status messages.

       -V,--version
              Display the version.

       -h,--help
              Syntax help.

knockd is the accompanying port-knock server.

knock[options]<host><port[:proto]>[port[:proto]]...