SOA means start OF Authority (authority origin) and is an entry in the zone file of a name server, which makes the DNS service available. The DNS service (Domain Name System) is one of the most important services in the Internet and is mainly used to accomplish a conversion of names in addresses. DNS is based on a distributed data base, in order to administer the name area. Usually of different reasons DNS Nameserver in Clustern are composed. The SOA entry in the zone file (thus in the file for the complete configuration and description of the domain), indicates now, which is autoritativ the server, i.e. which contains the newest information, so that all Slaves can synchronize accordingly.

Structure

A SOA resource record (SOA-RR) as well as contains parameter, those for the zone transfer of importance is main the names of the zone and the responsible Primary name server (short: Primary). Exactly a SOA-RR must be present in each DNS Zonendatei. Normally it stands completely at the beginning.

Example

example.com. 800 IN SOA master.example.com. hostmaster.example.com. 39 3600 1800 604800 1800 

In this example it is specified that a Slave synchronizes every 3600 seconds with its master for the zone example.com by zone transfer. If its master is not attainable, then every 1800 seconds a new attempt is started. If master cannot be within 604800 seconds (one week) to be contacted, then the Slave explains the zone example.com as inactive and answers no relevant DNS Requests more. DNS cached also missed Request. The TTL amounts to for this 1800 seconds.

Further it is defined that the Primary of this zone is master.example.com and that the administrator is attainable over the Mail address hostmaster@example.com ("“@"” must by one"”. "“to be replaced. (comes"”. "“before "“@"” forwards, e.g. vorname.nachname@example.com), then this becomes with one"” \ "“escaped - thus e.g. first name \ .nachname.example.com)). As standard (default) Time to Live for resource record of this zone is 800 given.

The serial number amounts to at present 39. During the next change it will be increased to 40.

Note

With the series number handling two procedures were established: Either one begins with 1 and increments with each change, or one carries in each case the current date with a two digit counter, more rarely also for the time (e.g. 2004052101 = 21. May 2004, first change on this day). Latter method is recommended in RFC 1912 2,2.

Related links

On-line Tools for querying the SOA data of arbitrary Domains (e.g. wikipedia.org):

• http://www.ip-plus.ch/tools/dig.cgi
• http://zonecheck.denic.de/

Articles in category "SOA resource record"

We found here 6 articles.

Related Websites

We found here 5 related websites.

• Chapter 8 - SOA Record
  The data contained in the SOA record applies TTL values to the slave DNS ... This value MUST change when any resource record in the zone file is updated. ...


• Cisco CNS Network Registrar User's Guide, 3.5 - Resource Records ...
  If you do not include a TTL, Network Registrar uses the zone default TTL, defined in the SOA resource record. Type


• FGA: The semantics of the fields of an "SOA" resource record
  The fields in (the data portions of) SOA resource records fall into four groups: ... They perform a series of SOA resource record lookups, starting with the ...


• Net::DNS::ToolKit::RR::SOA - Resource Record Handler - search.cpan.org
  Net::DNS::ToolKit::RR:SOA appends an SOA resource record to a DNS packet under construction, recovers an SOA resource record from a packet being decoded, ...


• Resource Records
  SOA Resource Record. The Start of Authority (SOA) record designates the start of a zone and ends at the NS records, but the SOA record must be at the root. ...