IPv6 priority in Windows and Apple issues

[joanandk]

Hi,

Version: 3.6.0 binary for Windows 11 and Apple (Mac OS, iOS)
Configuration 1:
remote <my_vpn>
remote <my_vpn> 443 tcp

Expected behavior: On a dual stack environment, connection to <my_vpn> via udp6, if the connection times out, then tcp6 should be tried. In a IPv4 only (for example Mobile) or failed IPv6 connection attempt it should use udp4. If those attempts fail, tcp4 should be the last resort.

Seen behavior:
Windows 11 on dual stack environment connects via udp4 to the server. In an IPv6 only, it connects via tcp6, it never tries to use udp6.
Mac Book on dual stack environment connects via udp4 (as Windows platform.). In an IPv4 only, connection fails with
"Endpoint address failmy (IPv6) is incompatible with transport protocol (udp4)"

Configuration 2:
remote <my_vpn> 1194 udp6
remote <my_vpn>
remote <my_vpn> 443 tcp

Expected behavior: As above.

Seen behavior:
Windows 11 on dual stack environment: Connection works as expected.
MacBook on dual stack environment works as expected, but in an IPv4 only environment, connection cannot be established and the error is
"Endpoint address family (IPv4) is incompatible with transport protokol (udp6)"

Did anyone noticed this behavior? As I do not have the infrastructure to compile the newest commit to test if it is already solved, I would appreciate your help.

BR

[joanandk]

Hi,
I now have compiled the 3.11 on MacOSX. The issue is still present. So I assume it doesn't work as expected?

I have tried openvpn 2.6 on Windows. This version behaves as expected. So I suppose that openvpn connect 3.6 has issues.

BR

[joanandk]

Solution to have UDP6->UDP4->TCP6->TCP4 on a dualstack network:
remote <my_vpn> 1194 udp
remote <my_vpn> 443 tcp

I was the impression remote <my_vpn> behaves like remote <my_vpn> 1194 udp, but it doesn't. It behaves like remote <my_vpn> 1194 udp4

[schwabe]

@joanandk no that is wrong. remote my_vpn behaves like remote my_vpn 1194 udp. If you see different behaviour that would be a bug.

Please include a full log and not just small fragments of a log.

[joanandk]

Version: 3.7.2 (4253) on Windows 11 (24H2)

Client configuration 1: Working.txt
This works in all type of environment (IPv4-only, dual stack, IPv6-only).
Log: OpenVPN_working.log

Client configuration 2: Not_Working.txt
This works on IPv4-only and dual stack, using only IPv4 for UDP connection. IPv6 does not work.
Log: OpenVPN_notworking.log

The difference is missing "1194 udp" in the configuration and "Endpoint address family (IPv6) is incompatible with transport protocol (udp4)" entry in the second log.

Hope these are the information you need. Otherwise I will provide more.

BR
PS: The IPs should not pose any privacy issue.

[joanandk]

@schwabe : I had a quick look into the source code. If I read it correctly, the default points to UDPv4.

BR