SOA (Start Of Authority) record

“SOA” (Start Of Authority) record is the first record in the zone file. An “SOA” record is only present in a zone file located on authoritative DNS servers.

 Every domain must have a Start of Authority record at the cutover point where the domain is delegated from its parent domain

“SOA” (Start Of Authority) specifies

• The primary authoritative DNS server for the zone (domain).

• The e-mail address of the zone’s (domain’s) administrator.

• Timing related information to the secondary DNS servers like refresh or expire interval, serial number to indicate the version of the zone file etc.

A sample forward lookup zone directive and forward lookup zone file is copied below. You can see the different Resource Records (RRs) like SOA, NS, A, and CNAME in the zone file.

The SOA record includes the following details:

  • The primary name server for the domain, which is ns1.dnsimple.com or the first name server in the vanity name server list for vanity name servers.
  • The responsible party for the domain, which is admin.dnsimple.com.
  • A timestamp that changes whenever you update your domain.
  • The number of seconds before the zone should be refreshed.
  • The number of seconds before a failed refresh should be retried.
  • The upper limit in seconds before a zone is considered no longer authoritative.
  • The negative result TTL (for example, how long a resolver should consider a negative result for a subdomain to be valid before retrying).

SOA Records have the following fields:

  • Name – This is the name that this record will have in the DNS Made Easy system, you will use this name to identify your record.
  • TTL – The number of seconds that this record will be cached in other servers.
  • Computer – The FQDN of the name server that was the original or primary source of data for this zone.
  • Email – A domain-name (FQDN) that specifies the mailbox of the person responsible for this zone.
  • Starting Serial – The starting serial number (the number version of your zone / domain). If you apply this SOA to a domain that is already created, the serial number will be incremented by one.
  • Refresh – The time interval (in seconds) before the zone should be refreshed. Recommended value – 86400 (24 Hours)
  • Retry – The time interval (in seconds) before a failed refresh should be retried. Recommended value – 7200 (2 Hours)
  • Expire – The time internal (in seconds) that specifies the upper limit on the time internal that can elapse before the zone is no longer authoritative. This is when the secondary name servers will expire if they are unable to refresh. Recommended value – up to 2419200 (672 Hours)
  • Negative Cache – The amount of time a record not found is cached. Recommended values can vary, between 180 and 172800 (3 min – 2 days)