SOA Record (Start of Authority)

The SOA (Start of Authority) record is the mandatory first record of every DNS zone. It names the primary nameserver, the administrator's contact, a serial number, and timers that govern zone transfers and negative caching.

Why it matters

Secondary nameservers compare the serial number to decide whether to fetch a new copy of the zone, so a serial that does not increase means changes may never reach them. The last field also sets how long resolvers cache "this name does not exist" answers (RFC 2308), which affects how soon a newly added record becomes visible.

Example

example.com. 3600 IN SOA ns1.dnshost.example. hostmaster.dnshost.example. (
    2026100501 ; serial
    7200       ; refresh
    3600       ; retry
    1209600    ; expire
    300 )      ; minimum (negative cache TTL)

The contact hostmaster.dnshost.example. means hostmaster@dnshost.example, with the first dot standing in for the @. A common serial format is YYYYMMDDnn.

Common mistakes

• Editing a zone file by hand and forgetting to bump the serial, or lowering it.
• Setting the minimum field very high, so a typo-driven NXDOMAIN is cached for hours.
• Treating the SOA as optional. A zone without one is invalid.
• Assuming managed DNS lets you edit it; most providers control these values for you.

Related

• NS record
• TTL
• Nameserver
• गाइड: DNS explained for website owners
• टूल: DNS checker

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