DNS FAQs

What exactly is DNS and what does it do?
What is an A record?
What is an MX record?
What is an SPF record?
What is Reverse DNS?

What is DNS?
DNS (Domain Name System or Domain Name Server) translates domain names meaningful to humans into the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices world-wide. An often used analogy to explain the Domain Name System is that it serves as the "phone book" for the Internet by translating human-friendly computer domain names into IP addresses.
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What is an A record?
An A record will directly translate a domain name into an IP address.

Example: isoc.net has an A record of 67.96.0.250. When you type isoc.net into a browser, the browser knows to go to the IP address of 67.96.0.250. because of the DNS.
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What is an MX record?
An MX record defines where to send any email sent to the domain. MX records don't use IP addresses, but rather a domain name.

Example: The MX record for isoc.net is mailin.isoc.net. So when someone sends an email to an email address at isoc.net, the MX records tells it to send it to the server mailin.isoc.net. However, as computers use numbers rather than words, just like any other domain, mailin.isoc.net also needs an A record so computers and servers know what IP address mailin.isoc.net is located at. So an additional A record is created for mailin.isoc.net that points to the IP address of 65.90.81.50.
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What is an SPF record?
SPF (Sender Policy Framework) is an authentication protocol designed to help fight spam. It works by checking to see whether email really comes from who it says it comes from in the email header. SPF works by adding additional information in a domain's DNS (Domain Names Server) record specifying which machines may legitimately send email for that domain. When mail servers receive email, they can check which computers are authorized to send mail for the domain of the email address in the From: field, and see if this message actually came from one of those authorized computers. If it did, the message is assumed to be legitimate and allowed through. If it did not, or if it is questionable, the receiving mail server can accept the message, mark it and accept it, or refuse to receive it.
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What is Reverse DNS?
A normal A record takes a host name (domain name or url) and translates it into an IP address. Reverse DNS does the opposite. It takes an IP address and translates it into a host name. A Reverse DNS entry is placed as a PTR record in the DNS of whoever owns the IP address.
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