What is an SOA record?
An SOA (Start of Authority) record is a mandatory DNS entry that appears at the beginning of every DNS zone file. It contains administrative information about the zone — including which server is the primary authority for it, who is responsible for managing it, and how secondary name servers should synchronise with the primary. Every domain that is served by DNS must have exactly one SOA record.
The SOA record does not directly affect how users reach your website, but it plays a critical role in how the DNS infrastructure behind your domain operates. It governs zone transfers, controls how long secondary servers cache zone data, and provides a serial number that signals when the zone has been updated.
What is a DNS zone?
A DNS zone is a distinct portion of the domain namespace that is managed by a specific organisation or administrator. Rather than storing all DNS records for the entire internet in one place, the global DNS system divides the namespace into zones, each handled by its own authoritative name server. A single zone can contain records for a domain and its subdomains, and a single name server can host multiple zones.
The SOA record is always the first record in a zone file. It defines the zone's administrative properties and is required for the zone to be valid.
Understanding the components of an SOA record
An SOA record contains several fields that work together to manage zone replication and caching. The primary name server (MNAME) identifies the main authoritative server that holds the master copy of the zone. The responsible contact field encodes an administrator's email address in dot notation — the first dot separates the local part from the domain, so admin.example.com means admin@example.com.
The serial number is a version counter that increments every time the zone is updated. Secondary servers compare this number to decide whether they need to fetch a fresh copy of the zone. The refresh rate is how often secondary servers check the primary for updates. The retry rate is how long a secondary waits before re-attempting a failed refresh. The expiry rate is how long a secondary considers its cached zone data valid before treating it as stale and stopping responses. The minimum TTL sets the default caching time for negative responses (NXDOMAIN) from resolvers.
How zone transfers use the SOA record
When a secondary name server wants to check for zone updates, it fetches the SOA record from the primary and compares the serial number to its own cached version. If the primary's serial is higher, the secondary initiates a zone transfer to fetch the updated records. This process keeps all name servers for a domain in sync without requiring manual intervention every time a DNS record changes.
How to use the SOA lookup tool
Enter any domain name and click Lookup. The tool queries DNS in real time and returns the full SOA record in a structured format — showing the host name, primary name server, responsible contact, serial number, TTL, and all timing values (refresh, retry, expiry, and minimum TTL). This is useful for auditing zone configuration, verifying that zone transfers are set up correctly, or diagnosing DNS propagation behaviour.
Frequently Asked Questions
Can I edit my SOA record?
Yes, SOA records can be modified through your DNS provider's control panel or by editing the zone file directly if you manage your own name servers. Changes should be made carefully — an incorrect expiry value, for example, could cause secondary servers to stop serving your zone prematurely. Always keep a backup of your zone file before making any changes, and increment the serial number whenever you update the zone so that secondary servers know to fetch a fresh copy.
What is the difference between an SOA record and an NS record?
An NS record identifies the authoritative name servers for a domain — the servers that hold and serve its DNS records. An SOA record, by contrast, contains administrative metadata about the DNS zone itself: who manages it, how often it should be replicated, and how long cached copies remain valid. NS records tell the world where to find your DNS data; the SOA record tells the DNS infrastructure how to manage that data internally.
What does the serial number in an SOA record do?
The serial number is a version identifier for the DNS zone. Every time a record in the zone is added, changed, or deleted, the serial number should be incremented. Secondary name servers compare their cached serial number against the primary's current serial to determine whether a zone transfer is needed. If the primary's serial is higher, the secondary knows the zone has been updated and requests a fresh copy.
What happens when the expiry rate is reached?
If a secondary name server has not successfully completed a zone transfer before the expiry time elapses, it will stop answering DNS queries for that zone entirely. This prevents stale or potentially incorrect data from being served to users. Once contact with the primary is re-established and a successful zone transfer completes, the secondary resumes normal operation.
How is the minimum TTL in an SOA record used?
The minimum TTL field in an SOA record was originally used as the default TTL for all records in the zone. In modern DNS, its primary function is to set the negative caching TTL — the length of time that resolvers cache a "this domain does not exist" (NXDOMAIN) response. A lower value means failed lookups are retried sooner; a higher value reduces query load but slows recovery after an incorrect NXDOMAIN response is cached.