Nameservers respond over TCP
ns.tcp
RFC 7766 makes TCP mandatory. Any answer too big for a UDP packet — DNSSEC, long TXT records, large MX sets — is retried over TCP, and a server that only speaks UDP silently fails those.
A longer write-up of this check has not been published yet. The report itself shows the raw evidence behind every result, which is usually the fastest way to see what was measured.
Run this check on a domain
Nameservers respond over TCP is one of 49 checks in every report, alongside delegation, mail authentication, TLS and registration.
Also in Nameservers
- Every nameserver is authoritative
- At least two nameservers
- Nameservers are independent of each other
- Nameserver hostnames are valid
- IPv6 reachability
- Nameservers are not open resolvers
- Nameservers agree on the SOA serial
- Nameservers agree on the NS set
- Nameservers respond over UDP
- Zone transfers are not open to the world