Start of Authority (SOA) is an important file of the Domain NameSystem( DNS) and stands for the start of a zone and thus for the management of zone files. The Start of Authority (SOA) is described in RFC 1035. The SOA record is located at the beginning of the Resource Record( RR) and identifies one of many Resource Record types.
The SOA record contains information about how the zone is managed and by whom. This includes information about the Origin, which is the name given to the machine where the data is deployed, and about the person in charge, the administrator or webmaster. Other information in the SOA record is the serial number associated with the date. This information is given in year-month-day and two- digit serial number. For example: 2009071203, where 03 represents the third change.
Furthermore, the SOA record contains the time for the Secondary Name Server (SNS) to synchronize with the Primary Name Server( PNS) and the time for the Secondary Name Server to retry if it does not reach the Primary Name Server. Both times are specified in seconds. So, for example, if a synchronization for the zone transfer is to take place every three hours, then the entry is 10800; if the server is not reached and a new attempt is to be made every hour, then the entry is 3600.
Another time specification is when the server cannot be reached. This time specification, also in seconds, can be for example 30 days, so the entry in the SOA record is 2592000. If the master cannot be reached in this time, then the zone is inactive and is no longer used. The Time to Live( TTL) to make the zone inactive is entered as default with 1800.
The complete SOA resource record looks like this: 2009071203 10800 3600 259200 1800.