# Next time when someone asks you, What happens when you enter google.com in your browser?

### 🧩 Step 0: The Goal

Your browser needs to find the **IP address** of [`google.com`](http://google.com) so it can connect to the web server.  
DNS is the system that helps it find that IP.

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### ⚙️ Step 1: Browser & OS Local Cache

When you type [`google.com`](http://google.com):

1. Your **browser** first checks its **own cache** (recently visited sites).
    
2. If not found, your **operating system** checks its **local DNS cache** (for example, your `/etc/hosts` file on Linux or Windows DNS resolver cache).
    

If found → done (no network query needed).  
If **not found** → move to the next level.

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### ⚙️ Step 2: The Resolver (Usually Your ISP or a Custom One)

Your computer sends the DNS query (like “What is the IP of [google.com](http://google.com)?”) to a **recursive resolver**.  
This is typically:

* your **ISP’s DNS resolver**, or
    
* a **public resolver** like `8.8.8.8` (Google DNS) or `1.1.1.1` (Cloudflare DNS).
    

This resolver’s job is to **find the answer** for you — it does all the hard work by asking other DNS servers in the hierarchy.

If it already has the answer cached → returns it immediately.

If **not cached** → it starts the **DNS resolution process** below.

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### ⚙️ Step 3: Root DNS Servers

The resolver sends a query to a **Root DNS Server**:

> “Hey, where can I find info about `.com` domains?”

Root servers don’t know about individual domains like [`google.com`](http://google.com),  
but they **do know where the Top-Level Domain (TLD) servers** are.

So the root server replies:

> “I don’t know [google.com](http://google.com), but here’s a list of `.com` TLD name servers.”

It returns a **referral** to the `.com` TLD servers.

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### ⚙️ Step 4: TLD (Top-Level Domain) Name Servers

Now, the resolver contacts one of the `.com` TLD servers:

> “Hey, I need info about [`google.com`](http://google.com) — who’s the authoritative server for it?”

The TLD server replies:

> “The authoritative name servers for [google.com](http://google.com) are [`ns1.google.com`](http://ns1.google.com), [`ns2.google.com`](http://ns2.google.com), etc.”

This is another **referral** — now we know where the **actual zone** for [google.com](http://google.com) is managed.

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### ⚙️ Step 5: Authoritative DNS Server

Finally, the resolver asks **Google’s authoritative name server**:

> “What is the IP address (A record) for [google.com](http://google.com)?”

This server owns the actual DNS records for [google.com](http://google.com).  
It replies with something like:

> “[`google.com`](http://google.com) → 142.250.190.14”

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### ⚙️ Step 6: Returning the Result

The recursive resolver now:

* Stores this result in its **cache** for some time (defined by the TTL).
    
* Sends the IP address back to your **computer**.
    

Your OS also caches it for a while.  
Then your browser uses that IP to make an **HTTP(S)** request to [`https://142.250.190.14`](https://142.250.190.14).

### Short Hierarchy:

| Step | Who | What it does |
| --- | --- | --- |
| 1 | Browser/OS | Check local cache |
| 2 | Recursive resolver (ISP/8.8.8.8) | Does the lookup chain |
| 3 | Root DNS | Points to TLD (.com) servers |
| 4 | TLD DNS | Points to authoritative server (for domain) |
| 5 | Authoritative server | Returns real IP |
| 6 | Response & Cache | Resolver → OS → Browser → You see the website |

Question :  
Why Caching Matters and what happens when cached?

Because of all following steps below, caching is critical for performance:

* Browser and OS caches: avoid repeated lookups.
    
* Resolver caches: millions of users share results.
    
* Each record has a TTL (time-to-live) after which it expires and must be re-fetched.