Domain Name Service (DNS) Terminology

 

1. What is a hostname?
2. What is a fully qualified hostname?
3. What is mailhost priority?
4. What is an IP address?
5. What is an A record?
6. What is a CNAME record?

---

What is a hostname?
The term hostname generally refers specifically to the part of the fully qualified name that does not include the domain name itself. For instance, if you owned example.com, you might want to have a host on your network called really-good. In this case, really-good would be the hostname, example.com would be the domain name, and really-good.example.com would be the full, or fully qualified hostname. See below for more information on the definition of a fully qualified hostname.

If you are entering a record in the Domain Management Tool that is for the domain itself (example.com in the example above), you do not need to enter a hostname, since the tool is smart enough to know that records without hosts belong to the domain. If you are specifying a hostname that will be part of your domain, make sure to enter only the host part of the name, with no trailing dots.

What is a fully qualified hostname?
In the hostname discussion above, a full hostname contained two parts, the specific name for a host called really-good that was part of the domain example.com.

If you are adding an MX record using the Domain Management Tool, you need to know the fully qualified hostname of the machine that will be receiving the mail. In this context a domain name could also be used as a hostname. If all of the services for your domain will be provided by the same machine you might want to make just "example.com." the hostname for your MX record.

More information about MX records can be found in the DNS MX Record FAQ.

What is mailhost priority?
When you have more than one mail server for a domain or hostname it is important to have a way to indicate which server should be tried first. If you have only one mail server there is no need to change the default priority (also known as preference) setting. If you have more than one, use lower numbers for the servers you want to try first. For instance, an MX record with a priority of 10 would be tried before a record with a priority of 20. You can also have more than one server with the same priority. In this case the remote mail server should pick one of them at random, effectively balancing the load between multiple servers.

More information about MX records can be found in the DNS MX Record FAQ.

What is an IP address?
In order to know where to send the packets that make up all kinds of communications on the Internet, the machines need to know the address of the other machines they need to communicate with. Think of the relationship between the hostname and IP address of a machine like the relationship between the name of one of your friends, and his or her telephone number. You know that if you want to reach your friend on the phone that you need to dial your friend's number, then the two phones will make a connection and you can begin your conversation.

Internet IP addresses have four parts, separated by dots. A typical example would be 209.132.13.42, which just happens to be the IP address of the Laguna Beach Internet home page.

What is an A record?
An A record is part of the zone file and is used to point Internet traffic to an IP address. For example, you can use an "A record" to designate abc.yourdomain.com to send traffic to your web site at IP address 209.132.X.XX. You can also designate xyz.yourdomain.com to go to a separate IP address.

What is a CNAME record?
A CNAME record is part of the zone file and is used to point Internet traffic to a hostname. For example, you can use a "CNAME record" to designate abc.yourdomain.com to send traffic to your web site at hostname.yourdomain2.com.