Login or Register

Networking

Devices receive IPv6 but some websites time out

troublesync_editorial
4w ago
Security
Performance
Environment

Environment

Fiber connection with native IPv6, OpenWrt router and Windows clients.

What happens

What happens

Most sites work, but selected dual-stack services pause and fail until IPv6 is disabled.

What I have tried

What I have tried

Changed DNS resolvers and rebooted the optical network terminal.

I would appreciate advice on how to identify the root cause without risking existing data or configuration.

Post timeline
COMMUNITY RESPONSES

Verified community troubleshooting

1 reply
0
jonasfixar Answer
user
Posted 2w ago • 0 confirmations

The important clue is that the problem only appears under the conditions you described.

Likely cause: Path MTU discovery is blocked, causing larger IPv6 packets to disappear.

What I would try: Allow required ICMPv6 traffic, verify the WAN MTU and configure MSS clamping only if the upstream link requires it.

Avoid applying several fixes at once, otherwise it will be difficult to know which one mattered.

Showing 1 of 1 community responses
AI DIAGNOSTICS

Incident analysis

Updated 4w ago• Trouble ID

Most likely causes

Path MTU discovery is blocked, causing larger IPv6 packets to disappear. 77%
A recent software, firmware or configuration change is exposing an existing compatibility issue. 31%

Summary

The reported behaviour is consistent with path MTU discovery is blocked, causing larger IPv6 packets to disappear. The safest next step is to verify that hypothesis with a reversible test before making permanent configuration changes.

Suggested Fixes

Verify the likely cause
Allow required ICMPv6 traffic, verify the WAN MTU and configure MSS clamping only if the upstream link requires it.
Validate and monitor
Reproduce the issue once after the change, review relevant logs or metrics, and keep a rollback path until the system has remained stable.

Continue troubleshooting

Related troubles

Matched from the title, description and tags

Edit trouble

Changes are recorded and can be restored later.

Tags · choose up to 10

Edit answer

Improve accuracy, clarity, and reproducibility.

Answer contentMarkdown

Report this trouble

Reports are private and help moderators keep the community useful and safe.

What is wrong?
Misuse of reports may restrict this privilege.

Revision history

Every entry contains the version that existed before that change.

No edits have been made yet.
Contact • Help • API Docs • Careers • Terms • Privacy • Cookies • Ads