DOKK / manpages / debian 12 / knockd / knock.1.en
knockd(1) knockd(1)

knock - port-knock client

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

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).

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.
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.
Output verbose status messages.
Display the version.
Syntax help.

knock 123:tcp 456:udp 789:tcp
knock -u 8284 4721 18592 42912

knockd is the accompanying port-knock server.

Judd Vinet <>
April 22, 2021 knockd 0.8