Network ports are logical connections, provided by the TCP or UDP protocols at the Transport layer, for use by protocols in the upper layers of the OSI model. The TCP/IP protocol stack uses port numbers to determine what protocol incoming traffic should be directed to. Some characteristics of ports are listed below:
• Ports allow a single host with a single IP address to run network services. Each port number identifies a distinct service.
• Each host can have over 65,000 ports per IP address.
• Port use is regulated by the Internet Corporation for Assigning Names and Numbers (ICANN).
ICANN specifies three categories for ports.
• Well known ports range from 0 to 1023 and are assigned to common protocols and services.
• Registered ports ...view middle of the document...
For example, if the server is only being used for e-mail, then shut down ports that correspond to FTP, DNS, and HTTP (among others).