Cerberus FTP Server licenses are per machine licenses. You will need one license for each machine you wish to install Cerberus FTP Server on.
By default, each license includes one year of support and upgrades. You can also purchase additional years of support with your license, or renew your support on an existing license before or after your support expires.
Purchasing multiple years of support with an initial license provides a discount over purchasing one year at a time.