Registro SOA

Structure of an SOA Record

Every DNS zone has exactly one SOA record at its apex. It contains the primary nameserver, the responsible party's email address (with the first . replaced by @), and five timing values: serial number, refresh interval, retry interval, expire time, and negative caching TTL.

The serial number is critical — secondary nameservers compare their copy against the primary's. If the primary's serial is higher, the secondary initiates a zone transfer to pull updated records. Most administrators use a date-based format like 2024032501 (YYYYMMDDNN).

Timing Parameters Explained

The refresh value tells secondaries how often to check for updates. Retry sets how long to wait before re-checking after a failed refresh. Expire tells secondaries to stop serving the zone if they cannot reach the primary within that window. The negative TTL controls how long resolvers cache NXDOMAIN responses for non-existent names.

When troubleshooting DNS propagation issues, the SOA serial is the first thing to verify. If your changes are not appearing on secondary servers, a stale serial is often the culprit. Use DNS Lookup to query a zone's SOA record directly and confirm the serial matches your authoritative source.

SOA records work closely with NS RecordName Server record. A DNS record that delegates a domain or subdomain to a set of authoritative DNS servers. Every domain must have at least two NS records for redundancy. to define zone authority and delegation. Understanding SOA timing is foundational before diving into zone transfer mechanics or TTL (Time to Live)A field in an IP packet header that limits the packet's lifespan by specifying the maximum number of hops it can traverse. Each router decrements the TTL by one; when it reaches zero, the packet is discarded to prevent routing loops. tuning strategies.