Quick answer: Compare the same site with IPv6 enabled and disabled, test a second device, and check router WAN IPv6 status before changing DNS or firewall rules.
Partial IPv6 failures usually involve router advertisements, prefix delegation, DNS, MTU, firewall rules, or an ISP path while IPv4 continues to work. Work through one test at a time so the result identifies the layer that is failing.
Why this happens
The best clue is the boundary of the problem: one file or every file, one device or several, one network or every network. Note when it began and any update, hardware change, permission prompt, or account alert that happened just before it.
- The router advertises IPv6 locally but has no working upstream route.
- The delegated prefix expired or changed after a reconnect.
- Path MTU discovery is blocked, so larger encrypted packets stall.
- Only one device has stale DNS, privacy address, VPN, or firewall state.
Fix it in the safest order
- Record affected domains and test them on a second device on the same network.
- Check whether the router has a global IPv6 WAN address and delegated LAN prefix.
- Restart the modem or ONT and router in provider-first order.
- Disable VPN and custom DNS for one controlled test; do not leave security off.
- Ask the ISP for supported IPv6 mode and MTU if the problem affects every device.
Repeat the same small test after each change. Keep a note of the original setting so you can restore it if the change does not help.
How to confirm the fix
IPv6 test sites and previously failing domains should load on two devices after router and client reconnection.
Common mistakes to avoid
- Do not copy an IPv6 mode from another ISP.
- Do not disable the firewall permanently.
- Do not assume changing DNS repairs a missing IPv6 route.
FAQ
Is it safe to disable IPv6 temporarily?
It can be a useful comparison and IPv4 may keep service working, but the lasting fix is correct router and ISP configuration.
Should I reset or reinstall everything?
No. A factory reset destroys useful evidence and is rarely the first step. Back up important data, test a second file, account, network, or device, and use the narrowest reset that matches the confirmed cause.
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