Windows – How to add persistent route for VPN when interface # varies

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In Windows, I can add a persistent route for an IP using the interface number of my VPN connection. However, when I reconnect to the VPN later, the interface number changes, which means the route I added previously no longer works. So each time I connect to the VPN, I have to re-add the route, using the VPN's current interface number.

For example, the VPN's route number may be 0x300003, then when I disconnect and reconnect, the route number becomes 0x320003, and so on.

Is there a way of adding a persistent route to the table which applies to a range of interface numbers? Or some other way of doing this without, each time I connect to the VPN, having to manually find the right interface # and re-add the route?

Best Answer

When multiple VPNs connect in random order, their interface IDs change. Therefor the normal ROUTE -P ADD 10.0.0.0 MASK 255.255.0.0 10.0.0.1 IF 42 does not work. The next time the VPN connects it might have a different interface number.

Powershell has a cmdlet available that adds routes on VPN connection and removes them again when the VPN is disconnected: Add-VpnConnectionRoute. It works without having to specify the interface ID.

The basic syntax is like this:

Add-VpnConnectionRoute -ConnectionName "VPN Connection Name" -DestinationPrefix 10.0.0.0/16

After entering this command, the routes will be created/removed automatically on connection/disconnection of the VPN.

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VPN – Creating a .bat File to Automatically Connect to VPN and Add a Route in Windows 7

I had tried to find any good working solution too and failed and after that I decided to write it by myself. You can use it if you still need it. http://www.latestbit.com/winvpnhelper

Windows – add a static route to a VPN network if the default gateway IP is dynamic? (Windows 7)

I've found out the answer myself:

You don't actually need to specify the default gateway - you can use the catch-all of 0.0.0.0 and then specify the interface number instead (the docs do not make this obvious!):

Find the interface number of the VPN by running "route print" from the command prompt and use this for the IF argument in the command below.
Add a static route for the IP range concerned using "route add" (with -p to make it permanent):

route add x.x.x.x mask 255.255.255.0 0.0.0.0 IF yy -p

Of course - you need to replace the IP address (x.x.x.x) and interface number (yy) in the command above with those relevant to your system.

Thankfully the VPN interface ID doesn't seem to change when you reconnect but it will be different from computer to computer.

"route print" should then show the desired static route with the gateway address as "On-link":

===========================================================================
Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
         10.0.0.0    255.255.255.0         On-link        1
===========================================================================

Best Answer

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VPN – Creating a .bat File to Automatically Connect to VPN and Add a Route in Windows 7

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