What is a DNS server? How Domain Name System servers connect you to the internet

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Summary List Placement

A Domain Name System (DNS) server is a fundamental part of the backbone of the internet — without it, it would be impossible to use a web browser to find websites.

You can think of the DNS server as a phone book. When you ask your computer to load a website, the DNS server matches the website’s name with the right IP address. This lets your computer find and load it properly.

How does a DNS server work?

When you enter a URL, what you’re really doing is asking your computer to find and connect to another IP address. To do this, it uses a set of related servers, all of which form the DNS server:

The DNS recursive resolver
The root nameservers
The TLD nameservers
The authoritative nameservers

Here’s how it works.

The DNS process, step-by-step

1. You ask your web browser to load a website. Since computers don’t speak English, your browser can’t read a name like “www.insider.com” and instead needs an IP address. Because of this, it sends your request to a DNS recursive resolver. The DNS recursive resolver’s goal is to find the IP address connected to the website you entered. 

2. The resolver’s first step is to find the website’s “Top Level Domain” or “TLD” — in other words, whether it’s a .com, .net, .org, or another type of site. It does this by asking the root nameserver, which keeps a list of every website in each TLD.

3. Once the resolver knows the TLD, it goes to the corresponding TLD nameserver (for example, the .com nameserver) and asks it to find the right IP address.

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4. The TLD nameserver finds the IP address and hands it off to the authoritative nameserver, which will figure out if that address is correct.

5. The authoritative nameserver sends a message to the address and waits for a response — if it gets the right response, then it has the right IP address for the website you want.

6. If the IP address is correct, the authoritative nameserver sends it back to your web browser.

7. Once your web browser receives the right IP address, your webpage starts to load.

All this happens in a matter of seconds — if your internet is very fast, or you’ve visited the website recently (see below for more information), it can happen in milliseconds.

Caching can avoid calling the DNS server

If you’re visiting a new website, your browser will go through the entire process outlined above. But if it did this for every single website, things could get slow — that’s why websites you’ve visited recently are stored in your web browser’s cache.

When you try to load a website, the DNS server will first check your cache to see if the IP address is already saved there. If it is, it’ll retrieve the IP address directly from the cache, which saves time. 

Each entry in the cache has a time limit associated with it, referred to as the TTL (time-to-live). The TTL for any IP address is generally about 48 …read more

Source:: Businessinsider – Tech


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