For those stumbling down a similar path…

tldr; Check that your Windows Firewall is turned off.

My setup

• OS: Windows 8.1 64-bit laptop
• OpenVPN: OpenVPN 2.3.4 x86_64-w64-mingw32

My OpenVPN has been working for at least 4 months without problem.

First thing to remind yourself is: When you get the VPN working – copy the OpenVPN log of a successful connection and the ipconfig /all to file so that you know what to compare when it breaks next time.

Notes

• The VPN connection stopped working yesterday 17/10/2014
• Not exactly sure when
• It had been working at my office
• My Windows 7 desktop has a working VPN setup so I can compare the settings
• The OpenVPN gui suggests a connection has been made but no sites can be pinged (see commands below)
• All attempts at inconfig /renew, ipconfig /flushdns nothing worked
• Only differences between Desktop/Laptop I could find in ipconfig /all and OpenVPN logs was that laptop had IPv6 for the WiFi connection turned off and the following extra fail message UDPv4: No Route to Host in the log
• I tried turning IPv6 back on but that didn’t change anything
• Now the UDPv4 message disappeared – but didn’t reappear when I turned off IPv6 again – so that was a red herring
• Possible suggestion from my history when first setting up my VPN (http://www.rickygao.com/troubleshooting-general-failure-in-ping-or-tracert/) was to turn off IPv6 which is what I’d probably done before – but IPv6 is no problem on my Windows 7 desktop
• Pinging even a specific IP address does not work – this confirms its not a DNS issue
• Pinging localhost 127.0.0.1 does work
• Pinging the IP Address of the connected VPN does work

C:\Users\Ian>tracert google.com
Unable to resolve target system name google.com.

C:\Users\Ian>ping google.com
Ping request could not find host google.com. Please check the name and try again.

Solution

Eventually found a solution that was to turn off the windows firewall, which came from this unbuntu forums post which eventually spotted that it was an iptables firewall issue.

Post mortem

• I thought I’d turned off my firewall and it doesn’t explain why the VPN stopped working
• Best guess is a Windows update changed something in the firewall the caused the problem
• The only Windows updates I received on 17/10/2014 were
• A failed update for Windows Malicious Software Removal Tool for Windows 8, 8.1 and Windows Server 2012, 2012 R2 x64 Edition - October 2014 (KB890830) – this was successfully installed the next day but didn’t help
• A successful Definition Update for Windows Defender - KB2267602 (Definition 1.185.3528.0)