What does ConnectTimeout in ssh_config mean?

Solution 1:

man ssh_config

/ConnectTimeout

ConnectTimeout Specifies the timeout (in seconds) used when connecting to the SSH server, instead of using the default system TCP timeout. This timeout is applied both to establishing the connection and to performing the initial SSH protocol handshake and key exchange.

Solution 2:

How I remember, Connection timeout is a time when server writing for connection if host unreachable. If you fill it by 0 and client will has connection problems server will close connection immidietly when clients connection losts