This is what a normal HTTP request looks like: https://www.google.com/api/search?q=home

Let's break it down:

— URL Structure

DNS Resolution

When we send the request, it is forwarded to a Domain Name Server that translates the URL to the IP Address of the machine where the website/service is running. Domain names are easier for humans to read and remember, so we use them. With every request, they are translated to their respective IP Addresses.

The browser does a DNS lookup to get the associated IP Address. When you enter a domain in the web browser address bar, you submit a DNS Request. The resolution process follows this order:

1. The operating system's DNS cache
2. Local hosts file
3. Browser cache
4. ISP cache

A DNS record is an IP address that matches the fully-qualified domain name.

— DNS Hierarchy

If not found in any cache, a DNS query or a request to a network of 4 DNS Servers is made. These servers include:

Recursive DNS Resolver

Its purpose is to forward a request to other domain name system servers and then send it back. When a request is received, it searches its cache. If not found, it is forwarded to the Root nameserver.

Root Nameserver

It identifies the Top-Level Domain and tells the DNS resolver to go to the correct TLD nameserver. There are exactly 13 Root Nameserver IPs managed by 12 different organizations globally, each with multiple servers to process incoming requests.

TLD Nameserver

It informs the resolver about the location of the IP address at a specific authoritative nameserver.

Authoritative Nameserver

It stores all information related to the domain name you want to visit in the form of zones, including its IP address. This IP is then cached and sent back to the user.

TCP Connection

After the resolution, the browser gets the IP address to connect to. It then:

1. Establishes a TCP connection with the server
2. If HTTPS, performs a TLS handshake for secure communication
3. HTTP/3 uses QUIC protocol instead of TCP

— TCP Connection

Sending the Request

The browser then compiles the request into HTTP specifications. A typical HTTP request packet looks like this:

GET /api/search?q=home HTTP/1.1
Host: www.google.com
User-Agent: Mozilla/5.0
Accept: text/html
Connection: keep-alive

Common HTTP verbs include:

Parsing the Request

The request is then parsed by the server to understand what needs to be done. It can be fetching data from the database, performing some calculations, or loading some files to send back.

A typical HTTP response looks like:

HTTP/1.1 200 OK
Cache-Control: max-age=3600
Content-Type: text/html
Content-Length: 1023
Set-Cookie: session=abc123

<!-- Content Body -->

Common Status Codes

Rendering the Response

The browser then parses the messages, extracts the information, and renders it on the Browser or Terminal. In case the browser can't render the document directly, it downloads it (like PDFs or other documents).

If the HTML contains CSS files, images, or JS code, subsequent requests are made to fetch these and render them on the browser.

Summary

When you enter a URL in your browser, several steps occur:

1. URL Parsing — Protocol, domain, path, query params
2. DNS Resolution — Convert domain to IP address (checking caches, querying DNS servers)
3. TCP Connection — Establishment with TLS handshake for HTTPS
4. HTTP Request — Sending and response handling
5. Content Rendering — HTML, CSS, JS processing