A typical SOA record in BIND format looks like this:
example.com IN SOA ns1.example.com. sysadmin.example.com. ( 2010121601 ; Serial (YYYYMMDD##) 3600 ; Refresh 900 ; Retry 1209600 ; Expire 3600 ) ; Minimum
The SOA record is defined in RFC 1035, and contains the following components:
MNAME The <domain-name> of the name server that was the original or primary source of data for this zone. RNAME A <domain-name> which specifies the mailbox of the person responsible for this zone. (By convention the @ sign is replaced with a period) SERIAL The unsigned 32 bit version number of the original copy of the zone. Zone transfers preserve this value. This value wraps and should be compared using sequence space arithmetic. (A common convention is YYYYMMDD## - where ## is a serial number for the change within the given day) REFRESH A 32 bit time interval before the zone should be refreshed. RETRY A 32 bit time interval that should elapse before a failed refresh should be retried. EXPIRE A 32 bit time value that specifies the upper limit on the time interval that can elapse before the zone is no longer authoritative. MINIMUM The unsigned 32 bit minimum TTL field that should be exported with any RR from this zone.