Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 233
SOA Record

The Start of Authority record is the first entry in the database file. This record indicates that the name server is the best-available source of information for this domain. For example:

The numeric entries above are indicated in seconds.

Notice that anything following a semicolon is ignored. The first entry on the first line indicates the domain this server is authoritative for: Naugle.com. The next field indicates the class of data in Internet (other types are defined, but not used today). The first name after the SOA indicates the primary name server for this domain, and the field after this indicates the person to contact. Replace the first “.” with the @ symbol and send an email there for more information. The information contained in the parentheses is for the secondary name server. For example, the serial number on the primary name server should be incremented when new information is placed in the database. In this way, the secondary servers will know they have old information and should be updated by this primary.

SOA Record

Notice that some domain names are written with or without a dot at the end. The ones with a dot on the end are known as absolute names and they specify a domain name exactly as it lies in the hierarchy name space starting from the root. Those names that do not end with a dot are domain names that may trail from some other domain. This is again, best exemplified through the directory system. To change directories in DOS or Unix, you use the CD (CHDIR) command. With this you can specify directly from the root which directory you would like to change to, or you can change directories relative to another directory. You do not have to type in the full directory pathname each time you want to change directories.

This is the same for DNS using the dot to signify the full pathname (with the dot) and relative to another pathname (without the dot).