Intermittend IPv6 connection failures

Dear Microsoft community,

on a machine running Windows 11 Pro 24H2 were IPv6 connections unavailable intermittendly. The browser connected via IPv4 with every website; pings failed when IPv6 was enforced. Typically this behaviour started about five minutes after plugging in the network cable and remained until plugging in and out the network cable.

Carrier: Vodafone 5G Router: ZTE MU5002 Browser: Mozilla Firefox 146.0 Location: Germany Local user account without admin rights Build: 26100.7462

The solution was resetting the firewall rules to default via Windows Defender Firewall with advanced security. And the network was set as a private network.

I think, there were no changes applied to the firewall rules manually. I don't know whether third party software applied changes to the firewall rules (there is some software installed which may do so, i.e. Wireshark, RustDesk, TeamViewer, WinSCP). The issue is gone for five days and didn't reappear so far (and I hope it won't reappear anymore).

This experience report might help people who face unavailability of IPv6 connections intermittendly.

Best regards

Jung-Fernmelder

Attachment: 4 screenshots