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DNS is the short form
for Domain Name System. It is basically an internet service to translate
domain names to IP addresses. Since the internet is mainly conisted
of numbers, it is difficult for the human brain to remember them.
Instead DNS service translates these numbers to a format which is
easier to remember.
is hosted on a server with IP address 220.127.116.11. If it were
not for DNS, users would have to type in these numbers in their
browser to access the site. This makes remember addresses difficult.
Thereby because of DNS, one can remember to goto DNSgoodies.com
instead of the IP address since the service translates this domain
name into its corresponding IP address.
If the internet were
based only on IP's then each IP address would be associated with
one website. For example, 18.104.22.168 would be locked to one
website. However, with the help of DNS, muliple websites can "share"
the same IP address. This allows multiple websites to be hosted
on the same server using the same IP address.
DNS is not only used
for viewing websites but is also integral in the relay of Email.
The DNS entries (namely MX record) indicates the address where email
is delivered much like how the address on a regular postal mail
indicates the destination. Without these DNS entries, our systems
would not know where to send the emails to.
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Different Types Of DNS Records
A Records (Address records)
MX Records (Mail eXchange Records)
CNAME Records (Canonical Name Records)
PTR (Pointer Records)
NS (Name Server Records)
SOA (Start of Authority Records)
In this tutorial, we shall only explain the first three.
Address Records (A Records)
A records resolves the hostname to its matching IP address. As
we talked earlier, its easier for humans to remember alphabets than
pure numbers, the A record is the DNS entry which accomplishes this
task. A few examples of A records are:
As you can see above it is possible to have multiple host names
assigned to the same IP address.
MX Records Top
MX records allow the email to be routed for a particular domain.
When a email is sent through a mail server, then it looks up for
this record of its destination address. An example of MX record
MX 10 mail.dnsgoodies.com
MX 20 mailhost.dnsgoodies.com
As you can see above, a domain can have mulitple MX records. This
ensures reliable mail delivery and allows for redundancy should
one of the mail servers fail. The numbers that you see (10, 20)
specify the priority of the mail servers to deliver the email to.
The email will first be attempted to send to the primary mail server
(in this case mail.dnsgoodies.com). If its unavailable, then the
email is then tried to be delivered to the secondary mail server
(mailhost.dnsgoodies.com). Notice that the higher the value of the
number, the lower the priority.
This record creates a canonical record of the real name of a host.
In other words, it assigns an alias to the canonical name. The alias
will inherit the properties of the original record. An example would
www CNAME dnsgoodies.com