Addressing and the web

The essentials

Every device on a network needs an address so that data reaches the correct destination. Two kinds of address are used: the physical MAC address and the logical IP address. Humans use easy names such as www.example.com, and the Domain Name System (DNS) turns these names into IP addresses.

Key points

• MAC (Media Access Control) address: a unique 48-bit (6-byte) physical address fixed on the NIC by the manufacturer. Written in hexadecimal, for example 3C-52-82-AF-11-0B. The first three bytes identify the manufacturer; the last three are assigned by the manufacturer to the card. It normally does not change.
• IP address: a logical address given to a device on a network, which can change when the device moves to another network.
• IPv4: 32 bits, written as four numbers from 0 to 255 separated by dots, for example 192.168.1.10.
• IPv6: 128 bits, written in hexadecimal groups separated by colons; created because IPv4 addresses were running out.
• Domain name: a readable name for a website, such as ncert.nic.in. The last part (.in, .com, .org, .gov) is the top-level domain.
• DNS server: looks up a domain name and returns its IP address. This process is called domain name resolution.
• Internet vs Web: the Internet is the worldwide network of networks (the infrastructure). The World Wide Web (WWW) is a collection of linked web pages accessed over the Internet using HTTP and browsers. Email and file transfer also use the Internet but are not the web.
• The web was invented by Tim Berners-Lee at CERN.

Exam tips

• Remember the numbers: MAC 48 bits, IPv4 32 bits, IPv6 128 bits.
• A value above 255 in any part makes an IPv4 address invalid.

Common mistakes

• Saying the Internet and the WWW are the same.
• Thinking the MAC address changes when you connect to a new Wi-Fi network; the IP address changes.