strange IPv6 behaviour on Windows

pent1ckel

Hi everyone,

I have a OpenVPN server running with dual stack.

Both protocols works perfectly. All my v4 and also v6 traffic gets routed to my tunnel and there is no other traffic on my normal interface.

Today I figured out that if there isn't an IPv6 address on my normal interface IPv6 isn't working at all.

OpenVPN setup the IP address on the TUN interface and also the routes are there. But for some reason is just don't work correctly.
When I try to ping the VPN server nothing happens. Also a ping from the OpenVPN server to the Windows hosts doesn't work. I could see with tcpdump on the Server site that the request coming in and the server tries to reply but it didn't reaches the Windows box. I also did a Wireshark on the Windows box and there I can't see any packets from the OpenVPN server at all.

The IPv4 connect through the tunnel is workin. Just IPv6 didn't work. When I move to a network where I have nativ v6 also activated also the tunnel IPv6 starts to work again.

I wasn't able to find anybody with the same problem. I tested on two Windows 7 boxes. I uses openvpn-install-2.3.8-I601-x86_64.exe on the Windows part.

If anything else would be needed please let me know.

Thanks in advance for some ideas.

Regards,
Bernd

Traffic

pent1ckel wroteIf anything else would be needed please let me know

configs and logs please.

pent1ckel

Hi everybody,

as I tried to reproduce all my steps and configured a new OpenVPN serve I also figured out that I missed one option.

But first here is my configuration because it is still strange:

openvpn.conf (server)

mode server
proto tcp-server
port 443
dev tun0
keepalive 10 60
persist-key
persist-tun
tcp-nodelay
verb 3
mute 20
status /var/log/badeio-vpn.log
tls-server
ca /etc/openvpn/ca-chain-sha1.crt
cert /etc/openvpn/badeio-vpn.crt
key /etc/openvpn/badeio-vpn.key
dh /etc/openvpn/dh4096.pem
tls-auth /etc/openvpn/ta.key 0
script-security 3
client-connect "/etc/openvpn/log-connects.sh"
client-disconnect "/etc/openvpn/log-disconnects.sh"
ifconfig 192.168.240.1 192.168.240.2
ifconfig-pool 192.168.240.0 192.168.255.255
route 192.168.240.0 255.255.240.0
auth-user-pass-verify /etc/openvpn/login.sh via-env
username-as-common-name
tmp-dir /tmp
client-cert-not-required
auth SHA512
cipher AES-256-CBC
tls-version-min 1.2
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"
push "redirect-gateway def1"
ifconfig-ipv6 2001:db8:a000:100:: 2001:968:a000:100::1
ifconfig-ipv6-pool 2001:db8:a000:100::2/64
push "route-ipv6 2000::/4"
push "route-ipv6 3000::/4"
management 127.0.0.1 31337 "/etc/openvpn/randompassword"

as everybody could see I missed the tun-ipv6 option on the server. Now the strange thing is: Linux, Android and iOS worked perfectly also with IPv6 and it doesn't matter if there is a nativ IPv6 connection or not. Only on Windows I had this strange behaviour that IPv6 only workend when there was Ipv6 already available and working on this box.

After I added tun-ipv6 to the server configuration it started to work in Windows all the time and it doesn't matter anymore whether there is an native IPv6 connection or not. Could this be a Windows limitation or something in the TUN/TAP driver of windows which communicates with the server?

For the record: my problem at all is solved but I still wondering what is different in Windows as it was working with other OSs

Thanks a lot and Regards,
Bernd