Companies that use Cloudflare Secondary DNS

What this captures, and what it doesn't

This dataset identifies companies using Cloudflare as a secondary authoritative DNS provider alongside their own primary DNS infrastructure. It is a fundamentally different deployment pattern from standard Cloudflare usage, and it targets a specific segment of the market.

Standard Cloudflare customers delegate their DNS entirely to Cloudflare — their nameservers become ns1.cloudflare.com and ns2.cloudflare.com. Secondary DNS customers do the opposite: they keep full control of their own primary DNS infrastructure and add Cloudflare as a redundant authoritative layer that receives live zone transfers via AXFR/IXFR. If the primary DNS goes down, Cloudflare keeps answering queries. It is a resilience feature, not a convenience one, and the companies that configure it are treating DNS as critical infrastructure rather than a commodity service.

This methodology does not capture:

• Companies using Cloudflare as their primary DNS provider — those appear in our main Cloudflare dataset, not here.
• Companies using other Cloudflare products such as the CDN, Zero Trust, or Workers without Secondary DNS configured.
• Companies that have Secondary DNS configured on internal or non-public zones where the nameserver records are not publicly resolvable.

Because Secondary DNS requires an Enterprise contract plus the Foundation DNS add-on, this dataset skews heavily toward large enterprises, government agencies, and financial institutions where DNS availability is a compliance or operational requirement.

How we detect it

The detection is a single DNS lookup. We pull the nameserver records for each domain and scan for the *.secondary.cloudflare.com pattern.

When a company enables Secondary DNS, Cloudflare assigns them one or more dedicated nameservers under the secondary.cloudflare.com subdomain — for example ns0227.secondary.cloudflare.com. These get added to the domain's NS record set alongside the company's own primary nameservers, producing a mixed record that looks something like this:

ns1.company.com
ns2.company.com
ns0227.secondary.cloudflare.com
ns0022.secondary.cloudflare.com

The *.secondary.cloudflare.com pattern is unambiguous — it does not appear in any other Cloudflare product or configuration. A match is a confirmed Secondary DNS deployment, with no further verification needed.

We run this check across the most popular domains belonging to roughly 3 million companies, ranked by headcount as reported on their LinkedIn company profiles.