[GGI] The Backroom: Using the DNS Information Interface

Using the DNS Information Interface
Modifying and maintaining your own DNS data may at first seem like a daunting task. However, some careful study of the examples below should help you understand enough about DNS to allow you to comfortably and confidently use the DNS Information Interface.

DNS database files are composed of many parts including the SOA (start of authority) record, NS (name server) resource records, A (address) records, CNAME (canonical name) resource records, MX (mail exchange) records, and a few others. Traditionally, these resource records are contained in a "zone file" which collectively define the DNS data for a specific domain name. Each line in the zone file is primarily composed of three parts: the name of the record, the type of the record, and the data that define the record. For example, the following lines represent a small section of an overall zone file:

berrett.org.            IN A      192.41.5.172
berrett.org.            IN MX     10 mail.berrett.org.
mail.berrett.org.       IN A      192.41.5.172
www.berrett.org.        IN A      192.41.5.172
ftp.berrett.org.        IN CNAME  www.berrett.org.

The previous lines list several address mappings (A records), a single mail preference definition (the MX record), and a canonical name alias (the CNAME record). More information about the A, CNAME, and MX records are found below.

Address (A) Records
The address record allows you to map a name to an Internet address. Every domain name has a primary address record (or at least should have) which associates the domain name with an IP address. Consider the following example:

berrett.org.            IN A      192.41.5.172

In the example above, the domain name "berrett.org" is mapped to the IP address "192.41.5.172". Additional address records are shown below:

berrett.org.            IN A      192.41.5.172
mail.berrett.org.       IN A      192.41.5.172
www.berrett.org.        IN A      192.41.5.172
GGI.berrett.org.    IN A      192.41.5.29

You will notice that the first three address records simply point to the same address of the origin domain name ("berrett.org"). However, the last address record, "GGI.berrett.org" points to a completely different Internet address, in this case the IP address of the Virtual Server. You can create address records which map names to any IP address that you desire.

Canonical Name (CNAME) Records
The canonical name record allows you to specify aliases for existing address records. Consider the following examples:

www.berrett.org.        IN A      192.41.5.172
ftp.berrett.org.        IN CNAME  www.berrett.org.
imap.berrett.org.       IN CNAME  www.berrett.org.
pop.berrett.org.        IN CNAME  www.berrett.org.
smtp.berrett.org.       IN CNAME  www.berrett.org.
support.berrett.org.    IN CNAME  www.berrett.org.
GGI.berrett.org.    IN A      192.41.5.29
hosting.berrett.org.    IN CNAME  GGI.berrett.org.

Where address records map a name to an address explicitly, canonical name records indirectly link names to IP addresses by referring to existing address records.

Mail Exchange (MX) Records
MX records specify a "mail exchanger" for a domain name. A mail exchanger is a host that will either process or forward mail for the domain name. MX records, like CNAME records, must refer to an existing address record. However, MX records differ from CNAME records in that they include an extra parameter, a preference value. The preference value is an number in the range of 0-65535 that indicates the mail exchanger's priority. For example:

berrett.org.            IN MX     10 mail.berrett.org.
mail.berrett.org.       IN A      192.41.5.172

The MX record specifies "mail.berrett.org" as the mail exchanger for the "berrett.org" domain name at a preference value of 10. The preference value itself isn't important, only its relationship to the values of other mail exchangers, i.e. is it higher or lower in value. Mailers will attempt delivery to the mail exchanger with the lowest preference value first. If delivery to the most preferred mail exchanger fails, mailers then attempt delivery to less preferred mail exchangers (those with higher preference values).

In most cases, the MX record we have set up for you will be all that you need. If you accidentally remove all MX definitions, most mailers will at least attempt to deliver mail to the host IP address.

Resource Record Abbreviations
Every DNS data file has what is called an "origin". The origin is basically the domain name of the DNS data file. For the "berrett.org" DNS data file, the origin is simply "berrett.org". The origin is appended to all names in the DNS data file that do not end in a dot. For example, these resource record definitions:

berrett.org.            IN A      192.41.5.172
berrett.org.            IN MX     10 mail.berrett.org.
mail.berrett.org.       IN A      192.41.5.172
www.berrett.org.        IN A      192.41.5.172
ftp.berrett.org.        IN CNAME  www.berrett.org.
imap.berrett.org.       IN CNAME  www.berrett.org.
pop.berrett.org.        IN CNAME  www.berrett.org.
smtp.berrett.org.       IN CNAME  www.berrett.org

can be shortened to:

berrett.org.            IN A      192.41.5.172
berrett.org.            IN MX     10 mail
mail                    IN A      192.41.5.172
www                     IN A      192.41.5.172
ftp                     IN CNAME  www
imap                    IN CNAME  www
pop                     IN CNAME  www
smtp                    IN CNAME  www

Basically, this shortcut allows you to remove all occurrences of the domain name in the resource record definitions.... except for the special case where the origin is the name, as in the primary address record and mail exchange record definitions above. There is another substitution you can make for this case, read on.

If the name in the resource definition is the same as the origin, the name can be specified as "@". For example:

berrett.org.            IN A      192.41.5.172
berrett.org.            IN MX     10 mail
mail                    IN A      192.41.5.172
www                     IN A      192.41.5.172
ftp                     IN CNAME  www
imap                    IN CNAME  www
pop                     IN CNAME  www
smtp                    IN CNAME  www

can be shortened to:

@                       IN A      192.41.5.172
@                       IN MX     10 mail
mail                    IN A      192.41.5.172
www                     IN A      192.41.5.172
ftp                     IN CNAME  www
imap                    IN CNAME  www
pop                     IN CNAME  www
smtp                    IN CNAME  www

The @ notation can be used on either side of the resource record type. Consider the following example:

@                       IN A      192.41.5.172
@                       IN MX     10 @
mail                    IN CNAME  @
www                     IN CNAME  @
ftp                     IN CNAME  @
imap                    IN CNAME  @
pop                     IN CNAME  @
smtp                    IN CNAME  @

One final note: The DNS Information Interface basically supplants your need to use the "Cname" Order Submission Wizard to request additional CNAME and address (A) records. When you use the order submission wizard, a "Cname" product is added to your account and you will be charged for that product. You can avoid this charge by using the DNS Information Interface and making the CNAME or address (A) record addition yourself. The "Cname" Order Submission Wizard will probably eventually go away.

Another Commonly Asked Question: The DNS Information Interface only allows you to edit zone file information for existing domain names that are associate with a Virtual Server you administrate. You can add additional domain names to your Virtual Server using the Domain Name Order Submission Wizard. Applicable Domain Name charges still apply.

A L S O S E E
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