Nameserver diversity and redundancy
Your domain should have at least two nameservers, on different networks, so a single outage cannot take your domain offline. RFC 2182 recommends this separation.
What the report checks
- Count: at least two nameservers (one is a single point of failure); a very large number is unusual and flagged for information.
- Subnets / diversity: the nameservers are not all in the same /24 (IPv4) or /48 (IPv6), and ideally not all on the same network or provider.
Why it matters
If all your nameservers sit in one rack, one data centre, or one provider, then that one failure makes your whole domain unresolvable: mail bounces, the site disappears. Spreading them across networks (or using an anycast DNS provider with many locations) removes that single point of failure.
How to fix it
Use your DNS provider's full set of nameservers, or add a secondary DNS provider and list its nameservers too (with zone transfer or an API sync between them). Make sure the parent delegation and your zone's NS records list them all.
How to verify
dig example.com NS +short
Resolve each nameserver's address and check they are not all in the same subnet or provider.