Allow Incoming Connection from Specific IP Address or Subnet in UFW

Allow Incoming SSH from Specific IP Address or Subnet

sudo ufw allow from 15.15.15.0/24  to any port 22

sudo ufw allow from 15.15.15.65 to any port 22

Allow Incoming Rsync from Specific IP Address or Subnet

sudo ufw allow from 15.15.15.0/24 to any port 873

Allow All Incoming HTTP and HTTPS

sudo ufw allow proto tcp from any to any port 80,443

Allow MySQL from Specific IP Address or Subnet

sudo ufw allow from 15.15.15.0/24 to any port 3306

Allow MySQL to Specific Network Interface

sudo ufw allow in on eth1 to any port 3306

References
https://www.digitalocean.com/community/tutorials/ufw-essentials-common-firewall-rules-and-commands