A Start of Authority (SOA) record is a type of resource record in the Domain Name System (DNS) that contains administrative information about a zone, especially regarding zone transfers. It is the first record in a DNS zone file and serves as a central point of authority for the zone.
Purpose of an SOA Record
The primary purpose of an SOA record is to provide information about who is responsible for managing the zone and how to contact them. It also includes information about when the zone was last updated and how often it should be refreshed.
SOA Record Format
An SOA record has the following format:
name SOA hostname ( serial number refresh retry expire minimum )
name: The name of the domain or zone.
SOA: The record type, which is always
hostname: The name of the primary authoritative name server for the zone.
serial number: A unique identifier for the zone that is incremented each time the zone is updated.
refresh: The time in seconds that should elapse before the zone is refreshed.
retry: The time in seconds that should elapse between retries if a refresh fails.
expire: The time in seconds after which the zone is considered no longer authoritative.
minimum: The minimum time in seconds that other name servers should cache negative responses for the zone.
How SOA Records Are Used
SOA records are used by DNS resolvers to determine the authoritative name servers for a zone and to update their cache of zone information. They are also used by name servers to perform zone transfers, which is the process of copying the zone information from one name server to another.
Example SOA Record
Here is an example SOA record for the domain
example.com SOA ns1.example.com. admin.example.com. ( 2023051701 10800 3600 604800 3600 )
This record indicates that the primary authoritative name server for the domain is
ns1.example.com and that the administrative contact for the domain is
[email protected]. The serial number is
2023051701, which means that the zone was last updated on May 17, 2023. The refresh interval is
10800 seconds, which means that the zone should be refreshed every 3 hours. The retry interval is
3600 seconds, which means that if a refresh fails, the name server should retry after 1 hour. The expire interval is
604800 seconds, which means that the zone is considered no longer authoritative after 7 days. The minimum caching time is
3600 seconds, which means that other name servers should cache negative responses for the zone for 1 hour.
SOA records are an essential part of the DNS system and play a critical role in maintaining the integrity and consistency of zone information.