Issue on 3.11 with TAP-driver and ip V6

[guillaume-lb38]

Hello,

When using openvpn3 (3.11 or 3.11.2) on windows 10 LTSC 2019, TAP driver (dco not available) I'm not able to communicate when server (2.6.3) assign an IPV6.

• before starting openvpn3, net adapater is available and not connected.
• after starting openvpn3 the client connect on server, get configuration, net adapater is marked connected and an ipV6 address is set.
• nc command executed on serveur not work (nc -6 -q 1 -w 1 ) .

If I change the server configuration to use IP V4, communication (nc) is ok (nc -q 1 -w 1 )

If I use openvpn 2.6.12 with ipv6, communication (nc) is ok (nc -6 -q 1 -w 1 ) .

I don't see any relevant error message in log except a route definition issue

Mon Jun 23 16:30:22 2025 TAP ADAPTERS:
guid='{915B103D-925B-41BD-AA78-DF962D2243A1}' index=3 name='OpenVPN TAP-Windows6'

Open TAP device "OpenVPN TAP-Windows6" PATH="\\.\Global\{915B103D-925B-41BD-AA78-DF962D2243A1}.tap" SUCCEEDED
TAP-Windows Driver Version 9.27
ActionDeleteAllRoutesOnInterface iface_index=3
netsh interface ipv6 delete route fc86:56bb:3d06:7189::/64 3 store=active
Ok.

netsh interface ipv6 set address 3 fc86:56bb:3d06:7189:32a9:60e:23d:f005 store=active

netsh interface ipv6 add route fc86:56bb:3d06:7189:32a9:60e:23d:f006/64 3 fe80::8 store=active
The parameter is incorrect.


action exception: nrpt_error: cannot open NRPT base key
DNS::ActionCreate interface name=[OpenVPN TAP-Windows6] search domains=[]
DNS::ActionApply: successful
ipconfig /flushdns

Windows IP Configuration

Is existing specific limitation or is it a bug ?