Addresses, the web and DNS

To send data to the right device, every node needs an address.

• MAC address: a permanent address built into the NIC by the manufacturer. It has 12 hexadecimal digits (48 bits). The first 24 bits identify the manufacturer, and the rest identify the card.
• IP address: a logical address given to a device on a network. It can change when the device joins a different network. An IPv4 address has 32 bits, written as four numbers from 0 to 255 separated by dots (such as 192.168.0.1), giving about 4.3 billion addresses. That is not enough for today's devices, so IPv6 uses 128 bits, written as eight groups of hexadecimal digits.

The Internet and the World Wide Web are not the same:

• The Internet is the global network of connected devices: the roads.
• The World Wide Web (invented by Tim Berners-Lee in 1990) is the collection of interlinked pages that travel over it: the traffic. It uses HTML to write pages, URLs (URIs) to name them, and HTTP or HTTPS to transfer them.

People remember names more easily than numbers, so websites have domain names, such as ncert.nic.in. But computers need the IP address. Converting a domain name into its IP address is domain name resolution, done by DNS servers.

DNS servers are arranged in a hierarchy. At the top are 13 root servers (named A to M), coordinated by IANA.