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PF
A SAMPLE FREEBSD / OPENBSD / NETBSD PF FIREWALL RULE ( /ETC/PF.CONF) Use the following to open port # 3306 on a BSD based systems:
pass in on $ext_if proto tcp from any to any port 3306
OR allow only access from your web server located at 10.5.1.3:
pass in on $ext_if proto tcp from 10.5.1.3 to any port 3306 flags S/SA synproxy state