How DNS Works?
DNS = Domain Name System or Service or Server
DNS resolves/maps a Name to an IP address
The diagram below describes the functionality of DNS. It also elaborates on what goes on behind the scenes once you type in a certain URL (Uniform Resource Locator) or a web address in your browser. The whole DNS process is based on the following 2 components:
- DNS Query (Question)
- DNS Reply (Answer)
DNS Flow Diagram
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How DNS Works?
A DNS is a server that translates domain names into IP addresses. Every website has its IP or set of IP address-numbers. The world wide web and the computers at all work more easily with numbers, on the other hand we as humans find it hard to remember any web address as a group of numbers. For example the website Google.com has its own address in numbers(IP address): http://64.233.167.104/
So if you type the address above, your browser won't connect to any DNS server just because the mentioned web address is in fact a set of numbers and the computers don't need "translation". That was de facto the case in the early days of the world wide web and Internet and Fidonet(already forgotten competitor of Internet in its early days(the internet), Fidonet actually used only numbers to refer to addresses, it used already the term "zone", which is essential to the DNS server operation, but we will discuss that later).
The first DNS appeared 1993, but years prior to the 90's, a group of Berkeley students invent BIND(Berkeley Internet Name Domain), which is at present the most popular DNS server.
DNS Records Explained: A, CNAME, NS, MX, and PTR.
A Records
Address (A) records direct a hostname to a numerical IP address. For example, if you want mycomputer.yourdomain.com to point to your home computer (which is, for example, 192.168.0.1), you would enter a record that looks like:
mycomputer.yourdomain.com A 192.168.0.1
PTR Record
The PTR Record (Pointer or Reverse Record) can be thought of as the opposite of an A Record. This is what allows a reverse DNS lookup, (where an IP Address is used to map, or determine what your host/domain name is).
Not every IP address has a corresponding PTR record, however they are sometimes required for diagnostic or security purposes. PTR records are added to reverse zone.
CNAME RECORDS
A CNAME (Canonical Name or Domain Alias)
CNAME allows a machine to be known by one or more hostnames. There must always be an A record first, and this is known as the canonical or official name. For example:
netcore.co.in. A 192.168.0.1
Using CNAME, you can point other hostnames to the canonical (A record) address. For example:
webmail.netcore.co.in. CNAME netcore.co.in.
pop2.netcore.co.in. CNAME netcore.co.in.
smtp3.netcore.co.in. CNAME netcore.co.in.
CNAME records make it possible to access your domain through webmail.netcore.co.in, pop2.netcore.co.in etc. Without a proper CNAME record, you will not be able to connect to your server using such addresses.
MX Record
An MX record (Mail Exchange Record), tells senders how to send email for your domain. When your domin is registered, it is assigned several DNS records. This enables it to be located on the Internet in several different ways. Every MX record points to an email server that is configured to process mail for that domain. Typically, one record points to a primary server, and additional records point to one or more backup servers. For users to send and receive email, the MX record for their domain must point to a server that can process their mail. This allows your mail to travel freely back and forth, arriving at the correct inbox.
Mx records are typically set up first with a priority. This priority can range from 0 to 99, with the lower the priority number, the more priority is given to that mail server.
Mail servers are normally named after the domain they serve with and follow general server naming conventions such as:
mail.YOURdomain.COM
pop3.YOURdomain.COM
smtp.YOURdomain.COM
imap.YOURdomain.COM
or anything set forth by your host, so check with them you you are not sure.
You can even have multiple MX records to handle incoming and outgoing mail, or as backup on another server etc.
Example
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netcore.co.in. 4299 IN MX 20 cluster8.netcore.co.in.
netcore.co.in. 4299 IN MX 5 cluster2.netcore.co.in.
netcore.co.in. 4299 IN MX 5 cluster6.netcore.co.in.
netcore.co.in. 4299 IN MX 10 cluster3.netcore.co.in.
How to check DNS records for domain.
Below are the free website on which DNS record can be check.
What if my domain name expires?
If domain has expired , website and email service will stop functioning.
To know whether the domain has expired or when domain is going to expire , check http://www.iptools.com/ "Whois Lookup(Domain)" option.
Enter the domain name here and see the "Expiration Date"
If domain has expired then get renew from your domain hosting server provider ( domain name registration )