The Internet and DNS
The internet is a global network of networks — a vast WAN connecting billions of devices worldwide. This lesson covers the structure of the internet, how data finds its way across it, and the critical role of the Domain Name System (DNS).
What is the Internet?
The internet is a worldwide collection of interconnected networks. It is not a single network owned by one organisation — it is a network of networks, linked together by routers, fibre optic cables, satellite links and other infrastructure.
Key facts
- The internet began as ARPANET in the late 1960s, a US Department of Defense research project.
- It uses TCP/IP protocols to enable communication between different networks and devices.
- The internet provides the infrastructure for services such as the World Wide Web, email, file transfer and streaming.
Important distinction: The internet is the physical network infrastructure (cables, routers, servers). The World Wide Web (WWW) is a service that runs on top of the internet — it is a collection of web pages accessed through browsers using HTTP/HTTPS.
How the Internet Works
IP Addresses
Every device on the internet is identified by an IP address (Internet Protocol address). There are two versions:
IPv4 — a 32-bit address written as four decimal numbers separated by dots.
- Example: 192.168.1.1
- Provides approximately 4.3 billion unique addresses.
- Addresses are running out due to the growth of internet-connected devices.
IPv6 — a 128-bit address written as eight groups of hexadecimal digits separated by colons.
- Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
- Provides approximately 340 undecillion (3.4 x 10^38) addresses — effectively unlimited.
- Designed to replace IPv4 as addresses run out.
| Feature | IPv4 | IPv6 |
|---|
| Length | 32 bits | 128 bits |
| Format | Dotted decimal (e.g. 192.168.1.1) | Hexadecimal with colons |
| Total addresses | ~4.3 billion | ~340 undecillion |
| Status | Running out | Gradually replacing IPv4 |
Routing
Data on the internet travels through many routers to reach its destination. Each router:
- Receives a data packet.
- Reads the destination IP address.
- Consults its routing table to determine the best next hop.
- Forwards the packet to the next router.
- This process repeats until the packet reaches its destination.
Data packets may take different routes across the internet and arrive out of order. The receiving device reassembles them into the correct order.
The Domain Name System (DNS)
Humans find it much easier to remember domain names (like www.bbc.co.uk) than IP addresses (like 151.101.0.81). The Domain Name System (DNS) translates human-readable domain names into IP addresses.
How DNS Works — Step by Step
- A user types a URL (e.g. www.bbc.co.uk) into their browser.
- The browser checks its local cache — if the IP address is stored from a previous visit, it uses that.
- If not cached, the request is sent to a DNS server (usually provided by the user's ISP).
- The DNS server checks its own records. If it has the IP address, it returns it to the browser.
- If the DNS server does not have the record, it queries other DNS servers higher up the hierarchy:
- Root DNS server — knows where to find information about top-level domains (.com, .co.uk, .org, etc.)
- Top-Level Domain (TLD) server — knows which server holds records for that specific domain
- Authoritative DNS server — holds the actual IP address for the requested domain
- The IP address is returned to the browser, which then uses it to connect to the web server.
- The DNS server and browser cache the result for faster future lookups.
DNS as a Distributed Database
DNS does not store all domain name records in a single location. It is a distributed database — records are spread across thousands of DNS servers worldwide. This provides:
- Resilience — no single point of failure.
- Speed — local DNS servers cache frequently requested addresses.
- Scalability — the system can handle billions of queries per day.
Hosting and Web Servers
When you visit a website, your browser connects to a web server — a powerful computer that stores the website's files and serves them to visitors.
Key concepts
- Hosting — storing a website's files on a web server so they are accessible via the internet.
- Web server — a computer running software (such as Apache or Nginx) that responds to HTTP/HTTPS requests.
- A single web server can host multiple websites (known as virtual hosting).
- Large websites use many servers, often in data centres, to handle high traffic.
The Cloud
Cloud computing means accessing computing resources (storage, processing power, software) over the internet rather than on your local device.
Examples of cloud services
- Cloud storage — Google Drive, Dropbox, OneDrive
- Cloud applications — Google Docs, Microsoft 365 Online
- Cloud hosting — Amazon Web Services (AWS), Microsoft Azure
Advantages of the cloud
- Access files from any device, anywhere with an internet connection.
- Automatic backups — data is stored remotely and backed up by the provider.
- Scalability — businesses can increase or decrease resources as needed.
- Collaboration — multiple users can work on the same file simultaneously.
Disadvantages of the cloud
- Internet dependency — no access without an internet connection.
- Security concerns — data is stored on third-party servers; there is a risk of data breaches.
- Ongoing costs — subscription fees may be more expensive long-term than owning local hardware.
- Privacy — users have less control over where their data is physically stored.
Summary
- The internet is a global network of networks using TCP/IP.
- Every device has an IP address — IPv4 (32-bit) or IPv6 (128-bit).
- DNS translates domain names into IP addresses using a hierarchical, distributed system.
- Web servers host websites; cloud computing provides remote access to resources.
Exam Tip: Be ready to describe the step-by-step process of a DNS lookup. This is a very common 4-6 mark question. Include: browser cache, DNS server query, root server, TLD server and authoritative server.
Deeper dive: addressing, DNS and the journey of a packet
The internet is a packet-switched network of networks. To make a request travel from your laptop to a server in another country, three layers of addressing co-operate: a MAC address identifies a device on its local link, an IP address identifies it on the global internet, and a domain name provides a human-friendly label that DNS resolves to an IP address.
IPv4 vs IPv6 — the address-exhaustion problem