Bulk nameserver diversity checker: is each domain's DNS a single point of failure?
In short: Paste domains and see each one's name servers, the provider domains they sit under, how many separate IPv4 networks they cover and whether any has IPv6. Limit: It reads DNS records only; it doesn't test whether any server answers.
A bulk nameserver diversity checker shows how spread out a domain's DNS is. Paste up to 100 domains, or 500 after a free Google sign-in, and each row lists the name servers, the provider domains they sit under, the number of separate IPv4 /24 networks and whether any server has IPv6, with a note on single points of failure. DNS only. Download the CSV.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. Check your list free nowSee pricing
Sample result
initech.example lists one name server; acme.example's sit under two provider domains.
- Domain
- initech.example
- Name servers
- 1
- IPv4 networks
- 1
What this means for you
One name server is a single point of failure for the domain's website and email.
- Name server count
- Provider domains behind them
- Distinct IPv4 /24 networks
- IPv6 noted; CSV out
- NS
- Redundancy
- DNS
By SimpleVerifier Team · Last updated
Auditing the email DNS of a domain list?
- Paste the domains here: up to 100 a run, or 500 after a free Google sign-in. Filter to the rows that need a fix and download the CSV.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I check the name server redundancy of many domains?
- Paste domains, email addresses or URLs, one per line, up to 100 a run or 500 after a free Google sign-in.
- Press Check name server diversity. Each domain's NS records are read, then the A and AAAA records of every name server, 10 domains a request. Nothing is sent to the name servers.
- Read each row: Several providers, One provider, Single point of failure, No NS records or Lookup failed, with each server's address counts.
- Filter to the single points of failure and download the CSV.
Example
- You enter
- Three domains:
acme.example(name servers at two providers),globex.example(two servers at one provider) andinitech.example(one name server). - You get
- acme.example: Several providers, with the provider domains and network count. globex.example: One provider, noted as common and not an error. initech.example: Single point of failure, with the reason. Download the CSV.
- Limits
- Up to 100 a run without an account and 500 when signed in with Google, counted over a minute. 10 domains a request; DNS only, nothing is sent to the name servers.
Why does name server diversity matter?
If a domain's DNS stops answering, its website, its email and everything else that depends on its records stop with it. Spreading the name servers over separate networks and, ideally, separate providers means one outage doesn't reach all of them. RFC 2182 advises placing secondary servers on different networks and in different places for exactly this reason.
For email the stakes are specific: if senders can't look up your MX, SPF or DKIM records, mail bounces or fails authentication.
How does this tool judge diversity?
It reads the NS records, resolves each name server, and counts three things: how many name servers there are, how many distinct provider domains their names sit under, and how many distinct IPv4 /24 networks their addresses cover. Fewer than two servers, fewer than two that resolve, or every IPv4 address in one /24 with no IPv6 is flagged as a single point of failure.
Two or more servers under one provider's domain is reported as One provider, which is common, works while the provider is up, and isn't an error. Several provider domains is reported as Several providers. To see who hosts each domain's DNS in the first place, use the bulk nameserver lookup.
What are the limits of the reading?
The provider is inferred from the name server's own domain, so a provider that uses several domains looks more varied than it is, and one that uses a single domain behind a global anycast network looks less varied than it is. Large managed DNS providers run many sites per name; that resilience isn't visible from addresses.
Treat the result as a prompt to look, not a score. To check that the servers actually agree with each other, use the bulk NS consistency checker.
Who uses this tool, and for what?
- DNS and infrastructure teams
- Find domains still served by a single name server or one network.
- MSPs
- Audit client portfolios for fragile DNS before an outage finds it.
- Email administrators
- Check that the zone holding your MX, SPF and DKIM records is resilient.
- Domain portfolio owners
- See which of many domains share one provider.
What can’t this tool tell you?
- It reads DNS records only; it doesn't test whether any server answers.
- The provider is inferred from the name server's domain.
- Anycast resilience behind one address isn't visible.
- Up to 100 domains a run without an account, 500 signed in.
Common questions
- How do I check name server redundancy for many domains?
- Paste the domains into a bulk nameserver diversity checker like this one. It reads each domain's NS records and their addresses and flags single points of failure, with a CSV of the results.
- Is this bulk nameserver diversity checker free?
- Yes. It is a free tool: up to 100 domains a run with no account, and up to 500 a run when you sign in with Google, with no card.
- How many name servers should a domain have?
- At least two, on separate networks. Many providers hand out two to four.
- Is one DNS provider a problem?
- Not an error. It is a dependency: if that provider has an outage, every domain on it is affected. Some teams add a second provider for that reason.
- Does it test whether the name servers answer?
- No. It reads their records, not their responses. The bulk NS consistency checker queries each server directly.
- Does it work on subdomains?
- A subdomain inside its parent's zone has no NS records of its own and shows No NS records.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.