Why can’t I control a Windows PC using Remote Desktop when connecting to it over VPN?

Anonymous August 21, 2014
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We need help with Remote Desktop over VPN. It fails when the target machine connects to an external network.

We have a Windows 7 machine on our LAN configured to accept remote desktop connections. That machine can also connect to a remote server via a VPN (VPN1).

When the client machine is on the physical LAN, it connects to the target machine, regardless of whether the target machine has a connection to VPN1. However, when the client machine is off the physical LAN and connected to it via VPN2, it can only connect to the target machine if the connection to VPN1 is not active.

I checked the port usage and VPN1 is not trying to take control of the RDC listening port. The IP addresses of these networks are all distinct, on separate domains:

LAN: 192.168.0.x
VPN1: 10.19.125.x (target RDC machine -> remote server)
VPN2: 192.168.2.x (client RDC machine -> LAN)

Does anyone have any ideas what might be going wrong? VPN1 is pptp and VPN2 is ipsec.

Thanks for any suggestions!

  1. David L
    September 1, 2014 at 3:28 am

    Thanks, Jan. That worked!

    It seems that the Windows 7 target machine was trying to send all traffic via VPN1. BTW, VPN2 connects to a Cisco router, rather than to a given machine (we have several computers on that network, and two of them are accessible via the VPN).

    Thanks again for your help.

  2. Jan F
    August 21, 2014 at 10:55 am

    Does the VPN2 connect directly to the target machine or to the network the target machine is on e.g. the Firewall? Personally I would try the latter if possible.

    Check if the Windows 7 target machine is trying to send all traffic via the VPN1:
    go into the properties of the VPN1 connection
    on the network tab open the properties of IPv4
    click advanced
    disable "Use default gateway on remote network"

    * I'm not sure which implication this might have on connections between the target machine and the remote server on VPN1.