knock - Man Page

• Knock on ports using different protocols: knock hostname portnumber:protocol
• Knock on port using UDP: knock -u hostname portnumber
• Force usage of IPv4/IPv6: knock -4|-6 hostname portnumber
• Display errors and details of connection: knock -v hostname portnumber

tldr.sh

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

knockd is the accompanying port-knock server.

Judd Vinet <jvinet@zeroflux.org>