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DNS tutorials

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.

Example: DNSgoodies.com is hosted on a server with IP address 206.113.12.227. 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, 206.113.12.227 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) Top

    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:

    dnsgoodies.com 206.113.12.227

    test.dnsgoodies.com 209.159.62.152

    domains.thisisatest.net 206.113.12.227

    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 is:

    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.

    CNAME Records Top

    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 be:

    www CNAME dnsgoodies.com