The server-side behavior of the sshd daemon is controlled by keyword settings in the /etc/ssh/sshd_config file and potentially the command-line options when sshd is started. For example, sshd_config controls which types of authentication are permitted for accessing the server.
The behavior on the client side is controlled by the Secure Shell parameters in this order of precedence:
User's configuration file ($HOME/.ssh/config)
System-wide configuration file (/etc/ssh/ssh_config)
For example, a user can override a system-wide configuration Cipher that is set to blowfish by specifying -c 3des on the command line.