What Is an SOA Record?
Understanding SOA (Start of Authority) records in DNS
Table of Contents
What Is an SOA Record?
An SOA (Start of Authority) record is a DNS record that provides authoritative information about a DNS zone. SOA records contain: primary name server (authoritative name server for the zone), responsible person email (contact email for the zone administrator), serial number (version number for the zone), refresh interval (how often secondary servers should check for updates), retry interval (how often to retry failed refresh attempts), expire interval (how long secondary servers should use cached data), and minimum TTL (default TTL for DNS records).
SOA records are essential for DNS zone management and authoritative DNS information. Every DNS zone must have exactly one SOA record at the zone apex.
Learn more about DNS and DNS zone management.
SOA Record Components
SOA records contain several components:
Primary Name Server
The authoritative name server for the DNS zone. This is the primary source of DNS records for the zone.
Responsible Person Email
Contact email for the zone administrator (format: admin.example.com, not admin@example.com).
Serial Number
Version number for the DNS zone. Incremented when zone data changes to trigger secondary server updates.
Refresh Interval
How often secondary name servers should check for zone updates (typically 3600 seconds).
Retry Interval
How often secondary servers should retry failed refresh attempts (typically 600 seconds).
Expire Interval
How long secondary servers should use cached zone data if primary server is unreachable (typically 604800 seconds).
Minimum TTL
Default TTL (Time To Live) for DNS records in the zone if not specified (typically 3600 seconds).
SOA Record Format
Record Format
SOA records follow this format: primary-nameserver responsible-person serial refresh retry expire minimum-ttl
Example SOA Record
ns1.example.com. admin.example.com. 2024010100 3600 600 604800 3600
Field Breakdown
- ns1.example.com.: Primary name server
- admin.example.com.: Responsible person email
- 2024010100: Serial number
- 3600: Refresh interval (seconds)
- 600: Retry interval (seconds)
- 604800: Expire interval (seconds)
- 3600: Minimum TTL (seconds)
Zone Apex
SOA records are always published at the zone apex (e.g., example.com) and must be present for every DNS zone.
SOA Record Uses
1. Zone Authority
SOA records establish authoritative information for DNS zones, identifying the primary name server and zone administrator.
2. Zone Synchronization
SOA records enable zone synchronization between primary and secondary name servers using serial numbers and refresh intervals.
3. Zone Management
SOA records provide zone management information, including contact information and zone versioning.
4. DNS Zone Requirements
SOA records are required for every DNS zone and must be present at the zone apex.
5. DNS Caching
SOA records specify TTL values that affect DNS caching behavior.
Checking SOA Records
1. DNS Lookup Tools
Use DNS lookup tools to query SOA records and retrieve zone information for domains.
2. Command Line Tools
Use command-line tools (dig, nslookup) to query SOA records: dig SOA example.com
3. Online Tools
Use online DNS lookup tools to check SOA records and verify zone configuration.
4. Domain Health Check
Use our domain health check to verify DNS configuration including SOA records.
5. Zone Verification
Verify SOA records are published correctly and zone information is accurate.
