Understand the two paths
An A record sends IPv4-capable clients to an IPv4 address, while an AAAA record supplies an IPv6 address. A service can therefore work perfectly for IPv4 tests while failing for clients that prefer IPv6. Test both paths separately instead of treating one successful result as proof of global availability.
Check the AAAA record first
Use DNS Lookup to confirm the AAAA record belongs to the intended hostname, is current and points to an address assigned to the service. Check for stale records, an unintended provider or an IPv6 address that belongs to an old server.
Verify IPv6 listening and routing
Confirm the web server listens on IPv6 and that the host, load balancer and upstream network advertise a usable route. An address being present in DNS does not prove that packets can reach the service or that the service accepts the connection.
Review firewalls and security controls
Check host, cloud, CDN and network firewall rules for IPv6 separately from IPv4. Security groups, rate limits and allowlists may support IPv4 but omit IPv6. Also check that monitoring and abuse protection do not block legitimate IPv6 traffic.
Check TLS and virtual hosting
The certificate must cover the hostname regardless of address family, and the web server must select the correct virtual host when the request arrives over IPv6. Test SNI, redirects and HTTP status on the IPv6 path, not only by opening the domain from an IPv4 network.
Inspect CDN and load balancer behavior
Confirm the CDN or load balancer has IPv6 enabled, publishes the intended AAAA record and can reach the origin over its configured path. If the edge supports IPv6 but the origin does not, behavior may differ between direct and proxied requests.
Fix or remove a broken AAAA
If IPv6 is not ready, temporarily removing an unreachable AAAA can restore access for affected users while you prepare the service. Do not leave a broken AAAA in place and rely on every client to fall back to IPv4. Publish it again only after end-to-end tests pass.
A repeatable dual-stack test
Query A and AAAA; test an IPv4 URL path and an IPv6 path; inspect status, time and certificate; compare results from an IPv6-capable network; check logs for the IPv6 client address; then retest after DNS cache and CDN changes update.
Check real data now
Use the live IIPP tool to inspect the domain or IP address you are working with.
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