By default, mySQL and MariaDB will communicate over port 3306.
If you have one or more firewalls between the client that wants to connect to mySQL or MariaDB and the system running mySQL or MariaDB, the port being used by mySQL or MariaDB will need to be opened/allowed in each firewall. For example, if firewalld sits between the client and mySQL or MariaDB system, and mySQL or MariaDB are using the default port 3306, here is how you would allow port 3306 in firewalld.
firewall-cmd --add-port=3306/tcp --permanent firewall-cmd --reload
To determine if mySQL or MariaDB are using default port 3306 or some other port, and mySQL or MariaDB is running on a Linux system, issue this command to determine the primary configuration file being used by mySQL or MariaDB. In this example, /etc/my.cnf is the primary configuration file being used by mySQL or MariaDB.
~]# mysql --help | grep /my.cnf | xargs ls ls: cannot access /etc/mysql/my.cnf: No such file or directory ls: cannot access /usr/etc/my.cnf: No such file or directory ls: cannot access ~/.my.cnf: No such file or directory /etc/my.cnf
Check the primary configuration file for the following directive. If the primary configuration file does not have the port directive, then default port 3306 is being used.
port = 3306