Doug Barton

DNS Terms

Copyright © 2002-2009 by Douglas Barton,, All Rights Reserved.
What is a hostname?
The problem with many common DNS terms is that they have more than one meaning depending on their context. In the context of adding resource records to a name server zone file, 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, you might want to have a host on your network called really-good. In this case, really-good would be the hostname, would be the domain name, and would be the full, or fully qualified hostname. See below for more information on the definition of a fully qualified hostname.

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 But that is only one example of a hostname, there are many other possibilities. One commonly accepted definition of a host is a machine on the Internet that can be reached from other machines on the Internet. However, in today's Internet world of virtual hosting for web and other services, load balancing technology and other tricks of the trade, the definition becomes more complicated.

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 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 MX record Frequently Asked Questions list.

What is an IP address?
In order to know where to send the packets that make up all kinds of communications on the Internet each machine needs 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 their 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 Protocol version 4 (IPv4) addresses have four 8-bit "octets", separated by dots. A typical example would be, which is the IPv4 address for

An IPv6 address has 8 fields of 16 bits each separated by colons. The IPv6 address for is 2001:4f8:fff6:0:0:0:0:28 which is more commonly written as 2001:4f8:fff6::28.

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