NS · SOA · serial
NS & SOA lookup
See which nameservers are authoritative for a domain and where they live, read the SOA timers in plain language, and check whether every resolver has picked up the latest zone serial.
Reading NS and SOA records
The NS records name the servers that hold the zone. Each one is resolved to its IPv4 and IPv6 addresses, so you can spot a nameserver that no longer exists or has no IPv6. If you enter a subdomain that is not its own zone, the tool explains which zone it belongs to and shows that zone’s nameservers.
The SOA record describes the zone itself:
- Serial: a version number that must increase with every change; many hosts use the date (2026102701).
- Refresh, retry, expire: how often secondary nameservers check for updates, how soon they retry, and when they give up.
- Negative TTL: how long resolvers cache “this name does not exist”.
The serial comparison asks all five resolvers for the SOA. One showing a lower serial still has an older copy of the SOA cached; it refreshes when the TTL next to it reaches zero.
Frequently asked questions
How many nameservers should a domain have?
At least two, and most registries require that. Ideally they sit on different networks so a single outage cannot take the domain offline (RFC 2182).
Why do resolvers show different SOA serials?
Each resolver caches the SOA for its TTL. One that fetched it before your last change still shows the old serial until that TTL runs out. Serials that stay different for long can also mean the nameservers themselves are out of sync.
Where do I change my nameservers?
At your domain registrar, which sends them to the parent zone. Changing the NS records inside your zone alone does not move the delegation.