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[Windows] Why are IPv6 DNS not pushed by our server in some cases?

This topic explains why, only with Microsoft Windows and only if Eddie is a version older than 2.16.3, Eddie sometimes shows this message:
Detected an OpenVPN bug (On-Link route on VPN range), autofix.


This issue occurs ONLY under Windows.

Sometimes (the problem is not systematically reproducible) after the VPN connection, inside IPv6 routing table entries you can see routes in identical ranges with different gateways:

>route -6 print
 38    259 fde6:7a:7d20:16::/64     On-link
 38    259 fde6:7a:7d20:16::/64     fe80::8

When this occurs, DNS6 can't be reached with subsequent delays and issues.

>ping fde6:7a:7d20:16::1
Pinging fde6:7a:7d20:16::1 with 32 bytes of data:
Destination host unreachable.

We think the problem is caused by an OpenVPN bug (at least in 2.4.4), currently under investigation.

Current workaround

Eddie automatically detects the issue and resolves it.

For those who don't use Eddie (and generate .ovpn files with Config Generator), our servers don't push DNS6 directive if Windows (or older versions of Eddie) is detected, until the issue is resolved in OpenVPN code.

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