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).

-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.

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