How does the OS X built-in firewall work?

The Disk Utility Repair Permissions feature repairs only the ownership and permissions for items installed by Apple. However, this may resolve issues with third-party products.

The Ping tab of Network Utility allows you to test basic connectivity to another network host by sending and then waiting for the return of a ping packet.

The OS X built-in firewall inspects each incoming network connection to determine if it's allowed. Connections are allowed or denied on a per-application basis.

Network services are established using a common network protocol. The protocol specifies which TCP or UDP port number is used for communications.