GlossaryDNS
Name server
Definition
A name server is the machine that holds a domain's DNS zone and answers authoritatively for it. The servers delegated to a domain are recorded at its registry, and those are the only ones that count.
What changing name servers really does
Changing name servers is not moving one line: it moves the whole zone at once. The site, the email, the verification tokens, all of it switches together to the new machine. Anything that was not recreated there beforehand simply vanishes, and the first thing to vanish is usually the MX records, because nobody thinks about email while migrating a website.
A domain declares at least two, and you want them on different networks wherever possible. This is not theoretical caution: if the only server answering becomes unreachable, the domain stops existing for the rest of the internet — no site, no mail, and no error message that explains why.
The delegation, as it is written
This is what the registry publishes for a domain: the servers it hands the answers to.
example.com. 172800 IN NS ns1.example.net.
example.com. 172800 IN NS ns2.example.net.Two servers, and a time to live of 172,800 seconds — two days. That long value, specific to delegation, is why a name server change takes far longer to show up than an ordinary address change inside the zone.
The usual mistake
Switching the delegation to the new host, then rebuilding the zone there. In between, the domain points at an empty or incomplete zone: the site goes down, and mail sent to the client bounces.
How to avoid it: Recreate the full zone at the new host first, compare it line by line with the old one — MX and TXT records included — and only then change the delegation. The order of those two steps is the whole difference between an invisible migration and an outage.
Source: The NS record and the delegation mechanism are defined in RFC 1034 and RFC 1035. The recommendation to spread servers across separate networks comes from RFC 2182.
Related terms
Where to go next
Knowing the words is half the job
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