What is a DNS SOA record?

DNS SOA Record (Start of Authority) is an authoritative record on the DNS server that contains important information about the DNS zone.

It provides information about:

  • Primary Server Name: The primary DNS server responsible for the zone.
  • Secondary Server Name: A backup DNS server that can be used if the primary server is unavailable.
  • Serial Number: A number that indicates the current version of the zone.
  • Expiration Time: The time duration during which the zone will be cached by the resolver.
  • Refresh Time: The duration of time during which the secondary server will check the primary server for updates.
  • Retry Time: The time duration in which the secondary server will retry if the primary server does not respond.
  • Maximum Expiration Time: The maximum time duration in which the zone will be kept in cache by the resolver.

Purpose of DNS SOA Record:

  • Provides authoritative information about DNS zones.
  • Helps prevent DNS lookup loops.
  • Ensures that DNS clients get the latest information about zones.
  • Helps manage zone replication between primary and secondary DNS servers.

Format of DNS SOA Record:

<zone name> SOA <primary server name> <secondary server name> <serial number> <expiration time> <refresh time> <retry time> <maximum expiration time>

Example DNS SOA Record:

example.com. SOA ns1.example.com. ns2.example.com. 2023030801 3600 1800 604800 86400

In this example:

  • example.com. is the zone name.
  • ns1.example.com. is the primary server.
  • ns2.example.com. is the secondary server.
  • 2023030801 is the serial number.
  • 3600 is the expiration time (1 hour).
  • 1800 is the refresh time (30 minutes).
  • 604800 is the retry time (7 days).
  • 86400 is the maximum expiration time (1 day).master.example.com. (2023030800; Serial Number 86400; Refresh 7200; Retry 3600000; Expire 86400; Negative TTL)

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