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Title: How DNS works


The Domain Name System (or Service, depending on who you listen to—DNS) is one of the most important components of modern networks, including the global Internet. Without it, you couldn‘t type into your Web browser; you‘d have to type a difficult to remember IP address instead.

DNS saves the day by translating human-friendly names into computer-friendly IP addresses. It actually does much more than that—providing computers with critical information about network services such as the locations of mail servers, domain controllers, and more.

The Process
In any DNS transaction, at least two computers are involved: the DNS server and a DNS client.
In most networks, there is often also a second DNS server known as the forwarder as well as additional authoritative DNS servers.

Consider an example: You‘re on your company‘s internal network, which is equipped with a DNS server. That server is set up to forward to your ISP‘s DNS server, and you‘re trying to surf to

Here‘s what happens:

1. Your client sends a DNS request packet, usually via User Datagram Protocol (UDP), to the local DNS server.

2. That DNS server has no clue what the IP address for is, so it sends the entire request to your ISP‘s DNS server—a process known as forwarding.

3. The ISP‘s DNS server also has no clue. However, it is configured with root hints, meaning it knows the IP address of a DNS server that is authoritative for the ―.com‖ toplevel domain (TLD).

4. The ISP‘s DNS server contacts the .com TLD server and asks for a reference for the domain. This action is called a recursive query. Your own DNS server could have performed this type of query, but it‘s more common for businesses to forward requests to their ISP‘s DNS server.

5. The TLD server, being authoritative, has records for every .com domain in existence (actually, there are a bunch of load-balanced DNS servers handling that TLD, but let‘s pretend it is one big server for now). So the TLD server sends back the IP address of a DNS server that‘s authoritative for the domain. Now the DNS server knows how to contact, so it just needs to figure out the www part.

6. The ISP‘s DNS server then contacts the DNS server. In all likelihood, that server is owned by Microsoft and contained in one of Microsoft‘s data centers (it‘s also probably part of another load balanced set of DNS servers because gets so much traffic). The ISP‘s DNS server asks for the address of

7. As an authoritative server for the domain, the DNS server has a record for the host named www. So it sends that host‘s IP address back to the ISP‘s DNS server.

8. The ISP‘s DNS server sends the IP address for to your local DNS server.

9. The local DNS server sends the IP address to your client.

10. You client now has the IP address, and can contact directly.

: basic dns concept, how dns function

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