DNS record types

Understanding SOA records

Every DNS zone has exactly one SOA (start of authority) record. It holds the zone's administrative settings and controls how long “not found” answers are cached.

Updated · Published by HostFaddy · 3 min read

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An example SOA record

example.co.za.  3600  IN  SOA  ns1.provider.co.za. hostmaster.example.co.za. (
                2026110201 ; serial
                3600       ; refresh
                1800       ; retry
                1209600    ; expire
                300 )      ; minimum / negative-caching TTL

The fields

FieldWhat it does
MNAMEThe primary nameserver for the zone.
RNAMEThe administrator's email address, with the first @ written as a dot: hostmaster.example.co.za means hostmaster@example.co.za.
SerialA version number for the zone. Secondary nameservers copy the zone when the serial increases. A common format is YYYYMMDDnn.
RefreshHow often secondaries check the primary for a new serial.
RetryHow long secondaries wait before retrying after a failed refresh.
ExpireHow long secondaries keep answering if they can't reach the primary at all.
MinimumToday this is used as the negative-caching TTL: how long resolvers remember that a name or record doesn't exist.

Why the SOA matters to you

  • New records seem “missing”. If somebody looked up a name before you created it, resolvers cache the “does not exist” answer for up to the negative TTL. A large value delays new subdomains.
  • Nameservers disagree. Compare the serial on each nameserver. Different serials mean a secondary isn't receiving updates.
  • Which provider is really in charge. The MNAME usually reveals the DNS provider.

With most hosting control panels and managed DNS services, the SOA is maintained automatically and the serial increases on every change.

Serial number mistakes

  • Editing a zone file by hand and forgetting to increase the serial. Secondary nameservers keep serving the old zone, so different visitors get different answers.
  • Accidentally setting a serial far in the future (for example a typo adding a digit). Every later serial is then “lower” and secondaries stop updating. Fixing it requires a controlled serial roll-over or reloading the secondaries — ask your DNS provider.
  • Assuming the serial must be a date. YYYYMMDDnn is a convention, not a rule. Many managed DNS services use a simple counter or a timestamp.

A worked example of negative caching

You plan to launch shop.example.co.za. Before creating it, you test the address in your browser. The resolver gets “no such name” and caches that answer for the negative TTL from the SOA — say 3,600 seconds. You then create the record. For up to an hour, that resolver (and anyone using it) still says the name doesn't exist, while people on other resolvers see it immediately. A smaller negative TTL, such as 300, shortens that window.

Looking up the SOA

dig example.co.za SOA +short
dig @ns1.provider.co.za example.co.za SOA +short   # compare across nameservers

Frequently asked questions

Do I need to edit my SOA record?

Usually not — your DNS provider manages it. You might lower the negative TTL if new records are often delayed.

Why must the serial number increase?

Secondary nameservers only copy the zone when they see a higher serial. If it doesn't increase, changes won't reach them.

What is a sensible negative TTL?

Values between 300 and 3,600 seconds are common. Shorter values make newly created records visible sooner.