FTP stands for File Transfer Protocol. It is a standard protocol used for transferring files over a network, particularly over the Internet. FTP allows users to transfer files from one host computer to another.

The basic FTP system consists of a client and a server. The FTP client is the software running on the user's computer that initiates file transfers, while the FTP server is the software running on the host computer that provides or receives the files.

FTP supports various operating modes, including active mode and passive mode. In active mode, the client initiates a connection to the server, while in passive mode, the server establishes a connection to the client. Passive mode is often used when the client is behind a firewall.

Users can authenticate themselves with FTP servers to gain read or write access to specific directories. There are also secure variants like FTPS (FTP Secure) and SFTP (Secure File Transfer Protocol) that use encryption technologies to ensure the security of the transmissions.

FTP is used for various purposes, including uploading files to a web server, downloading software updates, and general file exchange over the Internet.

An IP address (Internet Protocol Address) is a unique numerical identifier assigned to each device connected to a computer network that uses the Internet Protocol for communication. IP addresses are used to identify devices within a network and enable them to communicate with each other.

There are two types of IP addresses: IPv4 (Internet Protocol Version 4) and IPv6 (Internet Protocol Version 6). IPv4 uses a 32-bit number, while IPv6 uses a longer 128-bit number. A typical IPv4 address looks like this: 192.168.0.1, whereas an IPv6 address is more complex, such as: 2001:0db8:85a3:0000:0000:8a2e:0370:7334.

IP addresses are used to identify devices on the Internet and allow them to exchange data. They play a central role in routing data packets across the Internet, enabling information to be forwarded between different computers and networks.

The Domain Name System (DNS) is a hierarchical and distributed system designed to translate human-readable domain names into machine-readable IP addresses. It facilitates communication between computers on the Internet by managing the mapping of easily memorizable domain names to the numerical IP addresses that represent the actual communication targets.

Key functions of DNS include:

1. Name Resolution: The primary purpose of DNS is to resolve domain names to IP addresses. For example, when you access a website like "www.example.com," your computer uses DNS to find the corresponding IP address of that website.

2. Hierarchical Structure: DNS has a hierarchical structure evident in domain names such as "example.com." The hierarchy extends from right to left, with the right side being the Top-Level Domain (TLD), like ".com" or ".org," and the left side indicating specific subdomains (e.g., "example").

3. Distributed Database: DNS is decentralized and operates with a distributed database structure. There are multiple DNS servers distributed worldwide that collaborate to manage the mapping of domain names to IP addresses.

4. DNS Servers: Various types of DNS servers exist, including Authoritative DNS Servers, which provide authorized information for specific domains, and Recursive DNS Servers, which handle queries from clients and, if necessary, access Authoritative DNS Servers to obtain the required information.

DNS plays a crucial role on the Internet by providing a user-friendly way to access resources without users needing to know the underlying numerical IP addresses.