A port has the following characteristics −

• External devices are connected to a computer using cables and ports.
• Ports are slots on the motherboard into which a cable of external device is plugged in.
• Examples of external devices attached via ports are the mouse, keyboard, monitor, microphone, speakers, etc.

• A port number is the logical address of each application or process that uses a network or the Internet to communicate.
• A port number uniquely identifies a network-based application on a computer.
• Each application/program is allocated a 16-bit integer port number.
• This number is assigned automatically by the OS, manually by the user or is set as a default for some popular applications.

• The Domain Name System (DNS) is the phonebook of the Internet. Humans access information online through domain names, like wikitechy.com. Web browsers interact through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.
• Each device connected to the Internet has a unique IP address which other machines use to find the device. DNS servers eliminate the need for humans to memorize IP addresses such as 192.168.1.1 (in IPv4), or more complex newer alphanumeric IP addresses such as 2400:cb00:2048:1::c629:d7a2 (in IPv6).
• The DNS uses TCP Port 53 for zone transfers, for maintaining coherence between the DNS database and the server.