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I have created a VPN connection in Windows using the New Network Connection wizard that comes with Windows.

It works without problems in most places, but there is one concrete place where, despite the connection to the remote public IP works fine, it is not able to validate the login/password and establish the VPN connection.

In this place, the network is 10.0.0.x (the same I use in other places where I am able to connect). The remote network is 192.168.x.x, so I suspect there is some kind of IP collision, because before connecting, a traceroute to i.e. does not fail.

  1     4 ms     1 ms     1 ms  LINKSYS []
  2     5 ms     1 ms     1 ms
  3     4 ms     5 ms     3 ms
  ... (more)

I can't modify the local network further than the first router (

That is the only different I've found so far. Any idea about how to solve it? Thank you.

share|improve this question
You've got a bunch of private address spaces listed there - how about telling us all of the ipaddresses? What's the source local ip-address, what public (fully routeable, unlike the ranges you list above) addresses (if any) connect these private networks. Sounds like you have multiple sub-networks with duplicate addresses too, do you? – Helvick Feb 15 '10 at 19:54
Reminds of my apartment's free wi-fi. Linksys in each apartment (10.0.0.x), then a Netgear that those are all connected to (172.26.x.x), and then the ISP router those are connected to ( Triple NAT! – Bert Apr 2 '14 at 13:51
What error would appear when it tried to authenticate? The error code might be a clue. – Aaron Mason Jun 5 '14 at 6:34

Not doable. Simple like that. You can not route the same IP-Addresses. Fundamental issue - that should have been coordinated. This is why IPV6 has a new mechanism for determining your private address space to use.

In IPV4 private means private - the moment you couple multiple company networks it is not private anymore. If a colission occurs, you can:

  • Ignore it (the local space is not reachable by remote, but that may not be relevant, depending on what machines are there).
  • Coordinate (one must change) or
  • not use private addresses as they obviously are not in private use.

There is nothing else you CAN do.

share|improve this answer

I don't know what an IP collision is, but I suspect that the router at the network that doesn't work is blocking the VPN connection. Does the router have a VPN passthrough option? If so, is it enabled?

share|improve this answer
By IP collision I mean that the remote network is using the same 192.168.x.x addresses that also exist in the local network. The first router that is what I can control is a Linksys WRT54G with DD-WRT, I'll try to find that VPN passthrough option, thanks. – Guido García Feb 16 '10 at 8:06
That's what I thought you meant, but your post said that one network is 10.0.0x and the other is 192.168.x.x, so there's no "collision". This is a pretty common problem when both networks are using the same subnet, but in your case they aren't. – joeqwerty Feb 16 '10 at 12:38
Yes, but if you see the traceroute, there is an "underlying" 192.168.x.x network before trying to establish the VPN connection... Thank you for your answer. – Guido García Feb 16 '10 at 21:01
Yes, but that is part of your ISP's network and is not visible to the VPN client. If that were causing the problem, then half of the VPN connections in the world wouldn't work. The networks that the VPN connection transits have no bearing on the VPN connection itself. the VPN only knows about the local and remote networks and nothing about those networks in between. – joeqwerty Feb 16 '10 at 21:29
VPN passthrough is enabled, I've installed ddwrt-vpn and enabled that option, with no success. – Guido García Mar 26 '10 at 19:17

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