Updating zone file serial number convention alexandra hedison dating 2016
Increasing this value allows remote nameservers to cache the zone information for a longer period of time, reducing the number of queries for the zone and lengthening the amount of time required to proliferate resource record changes. Next, two nameservers are listed as authoritative for the domain.
It is not important whether these nameservers are slaves or if one is a master; they are both still considered authoritative.
The SOA defines the global parameters for the zone (domain). A Slave DNS does not use this TTL value but various parameters defined within the SOA RR - see below. Any name server that will respond authoritatively for the domain.
Only one SOA resource record (RR) is allowed in a zone file and it must be the first RR in the zone. ( 2003080800 ; sn = serial number 172800 ; ref = refresh = 2d 900 ; ret = update retry = 15m 1209600 ; ex = expiry = 2w 3600 ; nx = nxdomain ttl = 1h ) ; the following are also valid using @ and blank @ IN SOA ns. Called the Primary Master in the context of Dynamic DNS (DDNS).
Using this date format convention the value 2005021002 indicates the last update was on the 10th February 2005 and it was the third update that day.
The date format is just a convention, not a requirement, so BIND (or any other DNS software) will not validate the contents of this field.
By convention (in RFC 2142) it is suggested that the reserved mailbox hostmaster be used for this purpose but any sensible and stable email address will work.
In the jargon this field is called MNAME field which is why we called it name-server. Email address of the person responsible for this zone and to which email may be sent to report errors or problems.
In the jargon this is called the RNAME field which is why we called it email-addr.
A slave (Secondary) DNS server will read the master DNS SOA record periodically, either on expiry of refresh (defined below) or when it receives a NOTIFY and compares, arithmetically, its current value of sn with that received from the master.
If the sn value from the master is arithmetically HIGHER than that currently stored by the slave then a zone transfer (AXFR/IXFR) is initiated by the slave.