Bản ghi SOA
Start of Authority — metadata about the zone, including serial, refresh, retry and minimum TTL.
Bản ghi SOA là gì?
There is exactly one SOA per zone. It declares the primary name server, the responsible person's email (in DNS notation), and the timers that govern how secondaries refresh and how negative answers are cached.
Ví dụ mục zone file
example.com. 86400 IN SOA ns1.example.com. hostmaster.example.com. ( 2026010101 ; serial 3600 ; refresh 600 ; retry 604800 ; expire 300 ; minimum TTL )
Trường hợp sử dụng phổ biến
- ▸Diagnose stale secondaries by comparing their SOA serial to the master.
- ▸Set the minimum TTL for negative caching (RFC 2308) — prevents NXDOMAIN storms.
- ▸Audit zone changes: monotonic serial increments on every edit.
- ▸Validate ownership when transferring a zone between providers.
Lỗi phổ biến
The SOA serial must increase on every change, even after a reset. Many issues stem from forgetting to bump it. Format YYYYMMDDnn is conventional but not mandated.