Understanding DNS

In this article I want to discuss the various principles surrounding the Domain Name Structure, or DNS. Since computers only understand numbers and not words, they use DNS to translate domain names to IP addresses. Every device connected to the internet has an IP address. DNS is essentially the phone book for the internet. In a typical home network, when you type in http://www.google.com in your browser your local DNS server (usually your router) contacts your ISP’s DNS server in order to find out where google.com lives on the internet. If your ISP’s server doesn’t know where to find http://www.google.com it contacts the .com root server. The root server will have a record of google.com and will then ask google’s Name Server for the record of http://www.google.com. That information get’s relayed back to your PC allowing you to access http://www.google.com.

Root Server Chain of Command
There is a group of servers known as the “Root Servers” who’s purpose is to keep records of all of the Top Level Domains, or TLDs. There are 13 companies at the time of this writing that are responsible for managing all the root servers. Some current examples of TLDs include

.com
.gov
.us
.net
.co

And many more.  The root servers keep lists of Name Servers associated with each TLD.

DNS Records
A Record An A Record maps a domain name to the IPv4 address of the server where it resides

AAAA Record: The “Quad A” record is the same as an A record, but for mapping to IPv6 addresses.

CNAME Record CNAME record also known as an Alias record. It is used to map an alias to an A record. For example http://www.amazon.com is an alias of amazon.com since they both point to the same name servers. The C stands for canonical.

MX Records MX stands for Mail Exchanger records. If you want to send an email to your friend Bob and bob’s email is bob@gmail.com, your mail servers will retrieve the MX records from gmail’s DNS servers in order to locate the correct mail server to send to.

PTR Records PTR is the opposite of an A record. It maps an IP address to a domain. This can be useful with authenticating servers and prevent unauthorized access of a network.

To summarize, DNS allows computers to read URLs by translating them into IP addresses. These IP addresses are then used to direct internet traffic to the right destination, or web page.

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