The Internet: DNS, URLs and the Web Browser

The Internet and the World Wide Web

The internet is the global infrastructure of connected networks. The World Wide Web (web) is a service that runs on top of the internet — a collection of web pages stored on servers and accessed via browsers using HTTP or HTTPS. The internet also carries email, file transfers, video calls and many other services. The web is just one part of the internet, not the whole thing.

IP Addresses and the Problem They Create

Every device connected to the internet has an IP address — a unique numerical label such as 142.250.187.78. IP addresses allow routers to deliver data to the correct destination. However, humans cannot easily memorise long strings of numbers, which is why the Domain Name System exists.

The Domain Name System (DNS)

The Domain Name System (DNS) works like a phone book for the internet. When you type a web address, your device does not know the IP address of that server — it asks a DNS server to look it up. DNS is distributed across millions of servers worldwide so that no single server needs to know every domain name.

The DNS resolution process works in this sequence:

1. Browser cache check — the browser first checks its own cache. If you visited the site recently, the IP address is already stored locally.
2. Resolver (ISP’s DNS server) — if not cached, the request goes to a DNS resolver, typically provided by your ISP. The resolver also has its own cache.
3. Root name server — if the resolver does not know the address, it contacts a root name server. The root server does not know the final IP address, but it knows which server handles the top-level domain (e.g. .co.uk or .com).
4. TLD (top-level domain) server — the root server directs the resolver to the relevant TLD server, which handles all domains ending in .co.uk, .com and so on.
5. Authoritative name server — the TLD server directs the resolver to the authoritative name server for the specific domain. This server holds the actual IP address record and returns it to the resolver.
6. Response — the resolver returns the IP address to your browser, which then makes a direct request to the web server at that IP address. The result is cached for future use.

URL Structure

A URL (Uniform Resource Locator) is the full address used to locate a resource on the web. Each part of a URL has a specific meaning:

Consider the example URL: https://www.studyvault.co.uk/lesson/computer-science/networks

• Protocol: https:// — tells the browser which communication protocol to use. HTTPS indicates an encrypted, secure connection (HTTP without the S is unencrypted).
• Subdomain: www — the host within the domain, conventionally www for web servers.
• Domain name: studyvault.co.uk — identifies the organisation. The TLD (.co.uk) indicates a commercial UK site.
• Path: /lesson/computer-science/networks — the location of the specific resource on the server, like a folder path on a hard drive.

What a Web Browser Does

A web browser is the software that fetches and displays web pages. When you enter a URL:

1. The browser resolves the domain name to an IP address using DNS.
2. The browser sends an HTTP GET request to the web server at that IP address, asking for the web page.
3. The server responds with the HTML, CSS and JavaScript files that make up the page.
4. The browser’s rendering engine interprets the HTML structure, applies the CSS styling and executes the JavaScript to produce the page you see on screen.

Browsers also manage cookies (small files that store session data and preferences), maintain a browsing history and cache previously visited pages to speed up future loads.