How to select the VPN for an IP when the server has access to several VPN

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http://serverfault.com – I have a server (Windows server), which is in a private network. I need to connect to other VPN from another enterprise and access to a private URL of the other enterprise, but when I try to access that IP (10.-.-.-) the server can't reach it. I've tried to find how it's routed with "tracert" but the request keeps on waiting till the time for it expires. I've thought it can be a problem that the server is routing the request in it's own network rather than in the external VPN network. Is there any way to tell the server that I want to access the external VPN when accessing that IP? Can I use (HowTos)