Web Server Rescue
Read-onlyCompare A and AAAA Records
A site works for some users but fails for IPv6-capable clients, so you need to compare IPv4 and IPv6 DNS.
Command
printf 'A '; dig +short example.com A; printf 'AAAA '; dig +short example.com AAAABefore you run this
System impact: Read-only. Low when scoped to the shown target.
When not to use it: Do not remove IPv6 records without confirming the intended edge and provider behavior.
Expected output
The IPv4 and IPv6 DNS answers for the same hostname.
System impact
Read-only. Nothing changes. The command reads DNS and compares address families.
Recovery / rollback: no state is changed.
When to use it
Use when mobile networks, certain ISPs, or IPv6 clients report a different failure.
When not to use it
Do not remove IPv6 records without confirming the intended edge and provider behavior.
next steps
Related commands
Compare DNS Answers Across Resolvers
One resolver can still have the old edge IP while another has the new one.
for r in 1.1.1.1 8.8.8.8 9.9.9.9; do printf '%s ' "$r"; dig @"$r" +short example.com A; done
Compare Authoritative Nameserver Answers
The recursive resolver was not the problem. One nameserver disagreed.
for ns in $(dig +short NS example.com); do printf '%s ' "$ns"; dig @"$ns" +short example.com A; done
Check CAA Certificate Issuers
The certificate request failed because DNS allowed the wrong issuer.
dig +short example.com CAA
Check the WWW CNAME Target
The apex was right. The www name pointed through a different path.
dig +short www.example.com CNAME
Show the DNS Answer TTL
The fix was correct. The TTL explained why users still saw the old edge.
dig +noall +answer example.com A
Study mapping
Use this as independent command practice: read the notes, predict the output, then compare it with the example before using a real shell.
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.