Hope this is a suitable place to ask. I have a VPN connection set up on my home Windows 10 PC which lets me join the network at my office. At some point I noticed my internet connection seemed very slow and after a little bit of investigation discovered that Windows was routing all non-local traffic through the VPN.
I learned about the 'Use default gateway on remote network' checkbox in the IPv4 properties on the VPN connection, and have unchecked it. This solves the problem but only temporarily. After 'a while' (don't know exactly when it happens, I usually notice it within a couple of days) my internet connection feels slow again and sure enough all traffic is being routed through the VPN.
route print whilst the traffic is going through the VPN shows:
=========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.0.1 192.168.0.10 4506 0.0.0.0 0.0.0.0 On-link 192.168.12.200 26 220.127.116.11 255.255.255.255 192.168.0.1 192.168.0.10 4251 127.0.0.0 255.0.0.0 On-link 127.0.0.1 4556 127.0.0.1 255.255.255.255 On-link 127.0.0.1 4556 127.255.255.255 255.255.255.255 On-link 127.0.0.1 4556 192.168.0.0 255.255.255.0 On-link 192.168.0.10 4506 192.168.0.10 255.255.255.255 On-link 192.168.0.10 4506 192.168.0.255 255.255.255.255 On-link 192.168.0.10 4506 192.168.12.200 255.255.255.255 On-link 192.168.12.200 281 18.104.22.168 240.0.0.0 On-link 127.0.0.1 4556 22.214.171.124 240.0.0.0 On-link 192.168.0.10 4506 126.96.36.199 240.0.0.0 On-link 192.168.12.200 26 255.255.255.255 255.255.255.255 On-link 127.0.0.1 4556 255.255.255.255 255.255.255.255 On-link 192.168.0.10 4506 255.255.255.255 255.255.255.255 On-link 192.168.12.200 281 =========================================================================== Persistent Routes: Network Address Netmask Gateway Address Metric 0.0.0.0 0.0.0.0 192.168.0.1 Default ===========================================================================
My home PC is (statically assigned) 192.168.0.10, with 192.168.0.1 being my home router. The network I am joining through the VPN is 192.168.12.0, given an IP address by DHCP.
I can see it's added a route to use the VPN and given it the lowest metric. I don't know what 'On-link' means in this context.
The checkbox is still unchecked. If I disconnect and then reconnect the VPN connection, everything is fixed:
IPv4 Route Table =========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.0.1 192.168.0.10 281 188.8.131.52 255.255.255.255 192.168.0.1 192.168.0.10 26 127.0.0.0 255.0.0.0 On-link 127.0.0.1 331 127.0.0.1 255.255.255.255 On-link 127.0.0.1 331 127.255.255.255 255.255.255.255 On-link 127.0.0.1 331 192.168.0.0 255.255.255.0 On-link 192.168.0.10 281 192.168.0.10 255.255.255.255 On-link 192.168.0.10 281 192.168.0.255 255.255.255.255 On-link 192.168.0.10 281 192.168.12.0 255.255.255.0 192.168.12.1 192.168.12.200 26 192.168.12.200 255.255.255.255 On-link 192.168.12.200 281 184.108.40.206 240.0.0.0 On-link 127.0.0.1 331 220.127.116.11 240.0.0.0 On-link 192.168.0.10 281 18.104.22.168 240.0.0.0 On-link 192.168.12.200 281 255.255.255.255 255.255.255.255 On-link 127.0.0.1 331 255.255.255.255 255.255.255.255 On-link 192.168.0.10 281 255.255.255.255 255.255.255.255 On-link 192.168.12.200 281 =========================================================================== Persistent Routes: Network Address Netmask Gateway Address Metric 0.0.0.0 0.0.0.0 192.168.0.1 Default ===========================================================================
Only traffic for 192.168.12.0 is sent via the VPN, which is what I want.
Does anyone know what could cause Windows to keep suddenly deciding to ignore the 'Don't use remote gateway...' option and adding a route anyway?
Is there some kind of 'negative route' I can add permanently which effectively blocks any unwanted traffic going to the VPN?
Edit to add: I also tried manually setting the metric very high in the same page of the VPN IPv4 properties, but this seems to have no effect and is not reflected in the output of
Edit to add: I've also noticed another strange behaviour regarding connecting to the VPN. This is all using the built-in Windows 10 client:
If initiating the connection by clicking the network icon in the tray, selecting the VPN and clicking the inline 'Connect' button there, it will often get stuck at the 'Connecting...' stage for a while then fail.
If I go into the 'Netowrk & Internet Settings -> VPN' part of the control panel and initiate the connection from there, it succeeds 100% of the time and very quickly.
I have also been using a third-party utility called AutoVPNConnect, which periodically checks whether the VPN is active and 're-dials' it if not. I couldn't find any way to get this behaviour reliably within Windows itself. I now suspect that the unwanted route is being added when the utility re-establishes the connection. I don't believe it's doing this intentionally.
Possibly there are multiple APIs in Windows for 'dialling' a VPN, and they function slightly differently?
Edit to add: Manually assigning a metric of 1 to the local network interface, as suggested by harrymc, appears to have made the problem go away for at least a few days, even though
route print shows that Windows isn't actually using that value at all. Awarded the bounty to that answer as the suggest does seem to have stopped the problem, but I don't feel I can mark anything as the actual 'answer' to my question it still isn't explained why this happened, or why it has stopped, or whether it might come back in future.