How to Change the SOA Serial Number

Every DNS database file begins with a Start of Authority (SOA) resource record. Whenever you alter any data in a DNS database file, you must increment the SOA serial number by one integer.

For example, if the current SOA Serial Number in a data file is 101, and you make a change to the file's data, you must change 101 to 102. If you fail to change the SOA serial number, the domain's slave servers will not update their copy of the database files with the new information and the master and slave servers will become out of sync.

A typical SOA record of a sample hosts file looks like the following.

; sample  hosts  file
@	IN       SOA 	nismaster.doc.com. root.nismaster.doc.com. (
			109 ; Serial
			10800 ; Refresh
 	                1800 ; Retry
			3600000 ; Expire
			86400 ) ; Minimum

Thus, if you made a change to this hosts file, you would change 109 to 110. The next time you change the file, you would change 110 to 111.