knock

Port knocking client to open specific ports on firewall. More information: https://manned.org/knock.

• 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}}