Nameserver check: test delegation and nameservers
Check whether every nameserver of your domain responds, whether they all serve the same version of the zone and whether the delegation at the registry is correct.
Check nameservers
Enter the domain, for example your-domain.co.uk. For a subdomain we check the zone it belongs to.
Lookups run through the Quad9 DNS resolver (Switzerland). We keep the checked domain and an anonymised IP address for no longer than 30 days.
How nameservers work
What are nameservers?
Nameservers are the servers that give binding (authoritative) answers about your domain. Which ones they are is recorded in two places: at the registry of your extension, such as Nominet for .uk, and as NS records in your own zone. Both should match.
Why at least two?
If your only nameserver fails, resolvers can no longer resolve your domain once their cache expires – website and email included. That is why most registries require at least two nameservers, ideally in different networks and data centres.
What the nameserver check tests
We compare the delegation at the parent zone with the NS records of your zone, ask every nameserver directly for the SOA record and compare the serial numbers. Different serials show that a nameserver is serving an older version of your zone. Nameservers that do not answer authoritatively (lame delegation) are marked as errors.
Common nameserver mistakes
Delegation not updated after a move
After a change of provider, the registry still lists the old nameservers. The old DNS records then keep applying, whatever you enter at the new provider.
Nameserver does not answer for the zone
A listed nameserver does not know your domain at all (lame delegation). Resolvers asking it get errors or wait for timeouts.
Different SOA serials
A nameserver has not picked up changes. Depending on which server a resolver asks, it gets old or new records.
All nameservers in one network
If all nameservers sit in the same data centre, a fault there takes your domain completely offline. Spread them across different networks.
Frequently asked questions
Enter your domain above. The nameserver check shows every nameserver with its IP addresses, the delegation at the registry and, if we recognise it, your DNS provider.
That is when a nameserver is listed as responsible but gives no authoritative answers for your domain, for example because the zone was deleted there. Remove it from the delegation or set the zone up there again.
You change the delegation with the provider you registered the domain through. They pass the change on to the registry. Set up the zone completely at the new DNS provider beforehand so there is no gap.
At the registry the change is usually live within minutes. Resolvers, however, remember the old delegation until its TTL expires – for many extensions up to a day. During that time the old and new provider should have the same records.
It rises with every change to the zone, often in the format YearMonthDayNumber. Secondary nameservers use it to see that they need to reload the zone. If every nameserver has the same serial, they are in sync.
It is not mandatory, but recommended, as some resolvers can only be reached via IPv6. Most large DNS providers have offered IPv6 for a long time.
