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DNS
(Domain Name System) A system for converting host names and domain names into IP addresses on the Internet or on local networks that use the TCP/IP protocol. For example, when a Web site address is given to the DNS either by typing a URL in a browser or behind the scenes from one application to another, DNS servers return the IP address of the server associated with that name.
In this hypothetical example, WWW.CMSHOSTING.NET.AU would be converted into the IP address 216.118.117.16. Without DNS, you would have to type the four numbers and dots into your browser to retrieve the Web site, which of course, you can do. Try finding the IP of a favorite Web site and type in the dotted number instead of the domain name! BACK A Hierarchy
The DNS system is a hierarchy of database servers that start with the root servers for all the top level domains (.com, .net, etc.). The root servers point to authoritative servers residing within ISPs and companies that resolve the host names to complete the name resolution. Using the example WWW.CMSHOSTING.NET.AU, CMSHOSTING.NET.AU is the domain name, and WWW is the host name. The domain name is the organization's identity on the Web, and the host name is the name of the actual Web server within that domain. BACK Reverse DNS
(Reverse Domain Name System) Name resolution that is the opposite of the standard DNS query. Most of the time, the DNS is queried with a domain name to return the host's IP address. With reverse DNS, also called "inverse DNS," the DNS system is sent an IP address, and the domain name is returned.
Reverse DNS is used to log incoming traffic by domain name for statistical purposes. It is also used to prevent spam by determining if the e-mail message is coming from the domain name indicated in the message header. Reverse DNS is only an option and not mandatory in a DNS server. BACK DNS records
A DNS server is configured with a "zone file" for each domain that contains "resource records." There are several types of records, many of which can be managed here. BACK A Record
The Address (A) record associates a domain name with an IP address, which is the primary purpose of the DNS system. BACK
PTR Record
The Pointer (PTR) record provides data for reverse DNS, which is used for logging the domain name and verification purposes. Also called "inverse DNS," the PTR record is an option. Aliasing Names (CNAME)
The Canonical Name (CNAME) record is used to create aliases that point to other names. It is commonly used to map WWW, FTP and MAIL sub domains to a domain name; for example, a CNAME record can associate the sub domain FTP.CMSHOSTING.NET.AU with CMSHOSTING.NET.AU. BACK DNS Name Servers (NS)
The Name Server (NS) record identifies the authoritative DNS servers for a domain. A second name server is required for redundancy, and two NS records must be in the zone file (one for the primary; one for the secondary). The secondary server queries the primary server for changes. BACK Mail Servers (MX)
The Mail Exchange (MX) record identifies the server to which e-mail is directed. It also contains a priority field so that mail can be directed to multiple servers in a prescribed order. BACK
Text Record (TXT)
A TXT record can be used for any kind of documentation. It is also used to provide information to the SPF e-mail authentication system. BACK
First Record in File (SOA)
Start of Authority (SOA) is the first record in the zone file. It contains the name of the primary DNS server, which must correspond to an NS record in the file, the administrator's e-mail address and the length of time records can be cached before going back to the authoritative DNS server.
The SOA also includes data for the secondary DNS server such as the date of last update (the "Serial Number") and time intervals for checking the domain. BACK Common Zone File Resource Records
Associates With Type Name This
SOA Start of Authority (1st record)
A IPv4 Address subdomain 32-bit IP A6 IPv6 Address subdomain 128-bit IP AAAA** IPv6 Address subdomain 128-bit IP addressxxxxx
PTR Pointer IP address subdomain
CNAME Canonical alias name actual name
NS Name Server domain DNS server
MX Mail Exchange mail mail server
TXT Text (up to 255 characters of text)
** = First IPv6 A record, switched to A6 BACK
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Glossary 
