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