Understanding Basic DNS

What is a domain name?

A domain name is the unique human readable identifier for someplace on the internet. A domain name is read from right to left. The computer starts with the Top Level Domain, (TLD), which is the extention to the right of the ".". The most common TLDs are .com, .net, .org. The domain name is the full unique name: mysiteisdown.com. Anything to the left of the domain name is called a subdomain. For www.mysiteisdown.com, www is the subdomain. Some people use subdomains to list things like a blog, forum, or shop. If a website has many different subjects or users subdomains can be used in this manner as well such as guest.mydomain.com. The internet uses the domain name to find out where to locate the IP address.

What is DNS?

DNS, or Domain Name System is the set up that converts human readable web site names into something that computers can read. (Or computer readable addressing into something humans can remember depending on your point of view.) The internet reads the TLD, .com and knows to go to the server holding information about all .com domain names. The .com server looks at the full domain name and tells the internet who the registrar is. The registrar is the company that created records for the domain name to exist on the internet. The internet goes to the registrar and asks for the record corresponding to the domain name. Domain names must be associated with name servers. This is the information the internet needs. Name Servers are computers that hold databases of DNS records. Once the internet locates the name server, it can look up the individual IP address. An IP address is a unique set of numbers that computers use to identify the location of another computer. Think of it as a street address on the internet super highway.

What are DNS records?

DNS records allow the different parts of a domain to be located by the internet. A Zone File Record is the collection of individual DNS records for a single domain name.

The different types of DNS records:

There are many different types of DNS records, but most people have to worry about less than 10 types.

A Record: Address records point to IP addresses. Anything to the left of the "." on a domain name, needs to have an A record with an IP address, (this goes for name servers and MX records too). Most websites have an A record called www or ftp pointed to an IP such as 66.96.134.3.

MX Record: MX stands for mail exchanger. These records point email to the mail servers. An MX record should always be the name of the mail exchange, not an IP address. An example would be: mail.domainname.com or mx.domainname.com. MX records also have a priority that can be set. Priorities are most often set as multiples of 10, (10, 20, 30...). The lower the number, the higher the priority. Mail will always go to the highest priority server first.

CNAME : Canonical Name records act as an alias. It redirects a part of a domain name to someplace else. Some people may host a portion of their domain someplace else. For example shop.domain.com may be hosted with yahoo.com/shops and www.domain.com may be hosted with lunarpages.com. A CNAME allows a company to make any number of changes to their own IP address or DNS records without the customer having to make changes to their own DNS records. CNAMES are most often used by companies that do not offer full web or DNS hosting, as they expect to only host a small portion of a domain name.

NS Record: This is the name server information. The name server tells the Internet where to find all the different components related to your domain name. i.e., the web server, the mail server, etc. A name server record usually looks similar to ns1.securedns.com.

PTR Record: A pointer record is considered a reverse DNS record. It maps an IP address to a CNAME. This is often used to trace emails or a domain name. Many providers will block email if it has no reverse DNS to protect their clients from SPAM.

SOA: Start of Authority tells the internet how long to keep information about a domain name before it should look it up again, who is in charge of the DNS, what the Name Servers are, who to contact, when the DNS record was created, when the DNS record was last updated and any other relevant information.

What is an IP?

IP : Internet Protocol. Protocol used with data packet switching. Referred to as TCP/IP when discussing the internet protocol suite.

IP address: Internet Protocol address. An IP address is a unique set of numbers that computers use to identify the location of another computer. Think of it as a street address on the internet super highway. It refers to the computer readable addressing system. The most widely used is IPv4 an IP address using IPv4 will looks like this: 123.45.67.89. The newest system is IPv6 an IP address using IPv6 will looks like this: 2003:1df8:0:8a2e:85a3:9hf8:7433. The IP addressing system is broken up into classes and geographic locations.

IPv4 : Internet Protocol version 4. The computer readable addressing system. It uses a 32 bit addressing system in Dot-Decimal notation consisting of 4 octets. An IPv4 address is expressed as: 123.45.67.89.

IPv6 : Internet Protocol version 6. The computer readable addressing system. It uses a 128 bit addressing system consisting of 8 groups of 4 hexadecimal digits. An IPv6 address may be expressed as: 2003:1df8:0:8a2e:85a3:9hf8:7433.