If only some networks can reach a hostname, compare IPv4 and IPv6 explicitly. An A record and an AAAA record can point to different destinations, and a server can be correctly configured for one family while the other fails.
Make equivalent requests
curl -4 -I --connect-timeout 10 https://example.com/
curl -6 -I --connect-timeout 10 https://example.com/Replace example.com with your hostname. These commands request response headers over each family. The test machine needs working IPv6 to make the second result meaningful. Some applications handle HEAD differently from GET, so confirm with an ordinary request if needed.
| Stage | Check |
|---|---|
| DNS | The authoritative A and AAAA answers |
| Connection | Assigned address, route, listener and firewall for that family |
| TLS | Hostname coverage on the destination actually reached |
| HTTP | Virtual host and application configuration |
| Larger transfers | Path MTU behavior and relevant ICMPv6 handling |
Check the complete path
- Verify that the advertised IPv6 address belongs to the intended service.
- Confirm the application listens on the intended IPv6 address or socket.
- Review host and provider firewall policy for IPv6 separately.
- Test from a second known-working IPv6 connection.
- Record timestamps and exact errors before changing the public records.
IPv6 path MTU discovery relies on appropriate network feedback. Blocking essential ICMPv6 traffic can cause failures that are not fixed by allowing only the application port. Review the relevant network policy rather than disabling filtering indiscriminately.
Publish only a working destination
If the AAAA record is stale, correct it through the authoritative DNS provider. If IPv6 service is intentionally unavailable, remove an unsupported advertisement after reviewing the change. Do not label the entire hosting service down based on one failed family from one test network.
Check domain pointing and VPS networking for the DNS and host configuration steps.
Sources and references
Hosting documentation. Publication and update dates reflect this edition.
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