Soa updating zone files
The zone file may also contain various directives that are marked with a keyword starting with the dollar sign character. The parameters of the SOA record also specify a list of timing and expiration parameters (serial number, slave refresh period, slave retry time, slave expiration time, and the maximum time to cache the record).
The most notable is the $ORIGIN keyword, which specifies the starting point for the zone in the DNS hierarchy. Some DNS server software, such as BIND, also requires at least one additional name server record.
If the zone already exists, the imported record sets are merged with existing record sets. After you have verified that the zone has been imported correctly, you need to update the DNS delegation to point to the Azure DNS name servers.
For more information, see the article Update the DNS delegation.
A zone file is a sequence of entries for resource records.
A DNS zone file is a text file that contains details of every Domain Name System (DNS) record in the zone.
The field ttl (time-to-live) specifies the time after which a domain name client must discard the record and perform a new resolution operation to obtain fresh information.
If ttl is not specified, the global TTL specified at the top of the zone file is used.
This format was originally used by the Berkeley Internet Name Domain (BIND) software package, but has been widely adopted by other DNS server software – though some of them (e.g.
NSD, Power DNS) are using the zone files only as a starting point to compile them into database format, see also Microsoft DNS with Active Directory-database integration.