SOA Record Lookup
Look up any domain's SOA record and read the primary nameserver, hostmaster address, serial number, refresh, retry, expire and minimum TTL values, each with the record TTL.
About SOA Record Lookup
The SOA Record Lookup reads the Start of Authority record at the top of a zone and lays out its seven fields separately: the primary nameserver (MNAME), the hostmaster address (RNAME), the serial number, and the refresh, retry, expire and minimum timers, alongside the TTL of the record itself. Those numbers govern how secondaries track the zone and how long negative answers stay cached, so they are the first thing to check when a zone edit has not reached every authoritative server.
SOA is defined in RFC 1035 and its fields have precise operational meanings. Refresh sets how often a secondary polls the primary's serial, retry how long it waits after a failed poll, and expire how long it may keep answering for the zone without a successful transfer - once expire passes the secondary stops serving and answers SERVFAIL. Minimum was redefined by RFC 2308 as the negative-caching TTL, so it controls how long NXDOMAIN answers persist. In practice most primaries also send NOTIFY (RFC 1996), so transfers start sooner than refresh alone suggests.
The lookup runs server-side through our own European resolver, with a second resolver as fallback, and returns the SOA exactly as the zone publishes it: MNAME, RNAME, serial, refresh, retry, expire and minimum in RFC 1035 order, plus the record's TTL. It reports one answer, which is what a resolver would use, so it will not tell you whether every authoritative server agrees. For that comparison use Domain DNS Validation or the DNS Delegation Trace, both of which query each nameserver directly and line up their serials.
How to use it
- 1Enter the zone apex, for example example.eu rather than www.example.eu, because the SOA lives at the top of the zone.
- 2Select Lookup to query the record through our European resolver.
- 3Read the Value column: the fields appear in RFC 1035 order as primary nameserver, hostmaster, serial, refresh, retry, expire and minimum.
- 4Compare the serial with the value your DNS provider shows after an edit; if it has not moved, the change was never published.
- 5Check the TTL column to see how long this SOA can stay cached, and the minimum value for how long negative answers will.
Common use cases
- -Confirming a zone edit was actually published by checking that the serial has incremented.
- -Troubleshooting a secondary nameserver that keeps serving stale records after a failed zone transfer.
- -Auditing refresh, retry and expire timers against the operational guidance in RFC 1912 before handing a zone over to a client.
- -Planning a DNS provider migration by reading the current expire value to know how long secondaries can survive without the primary.
- -Checking the negative-caching TTL when an NXDOMAIN answer for a newly added hostname refuses to clear.
Frequently asked questions
- What is an SOA record used for?
- SOA marks the start of a DNS zone and carries the parameters secondaries and resolvers rely on: the primary nameserver, the hostmaster mailbox, a serial that versions the zone, and the refresh, retry, expire and minimum timers. Every zone has exactly one SOA at its apex, and resolvers also return it with negative answers to state how long an NXDOMAIN may be cached.
- What does the SOA expire value do?
- Expire is the ceiling on how long a secondary may keep answering for a zone when it cannot reach the primary. Each failed refresh leaves the secondary serving its existing copy; once the expire interval passes with no successful transfer it discards the zone and returns SERVFAIL instead. One to four weeks is common, because too short an expire turns a long primary outage into a full domain outage.
- Why do my nameservers show different SOA serials?
- Different serials mean at least one secondary has not completed a zone transfer. The primary increments the serial on every change and notifies its secondaries (RFC 1996); if the NOTIFY is dropped, an AXFR or IXFR is blocked by a firewall or ACL, or the transfer simply fails, that server keeps serving the previous version of the zone. Resolvers may reach either server, so the symptom is a change that appears to work intermittently.
- Is the SOA minimum field the same as the default TTL?
- Not since RFC 2308. It originally supplied a default TTL for records that lacked one, but it now specifies the negative-caching TTL: how long a resolver may cache an NXDOMAIN or NODATA answer for names in the zone. A zone file's default TTL is set separately with $TTL. A large minimum means a hostname you have just created can stay unresolvable for some time after you add it.