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device to device VPN from office to office of a different network, but the same subnet

Posted on 2006-11-27
Last Modified: 2010-04-12
I am trying to implement a VPN (device to device) from one office ( subnet to the other office ( subnet The devices have been configured, and the policies have been created, but the tunnel never gets initiated.
I ran this by someone that's told me that I'd at least have to change the subnet of one office, in order to get it to work. Is this true?
If both networks are going to route requests for the other network through the vpn device (router), because they are addresses outside of their range, how could this be true?

Thank you in advance.
Question by:effincomputers
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LVL 77

Expert Comment

by:Rob Williams
ID: 18022877
VPN's require that the local LAN at either end of the tunnel use different subnets. Commonly someone might use something like: with subnet mask of and with  Your configuration also segregates the 2 network segments by putting them on different subnets which is fine and should work well, assuming you are aware the "normal" usable IP's are and The other IP's in those subnets are the network ID and Broadcast IP. The routers will take care of the routing between subnets. That is what they do. Perhaps there is another issue.

What are you using to create the VPN tunnel?

Author Comment

ID: 18023231
Hi Rob. Thank you for your response.
I can troubleshoot the details. I just want to make sure that I'm not missing something here.
So you agree that the scenario I described is possible (factoring in the net ID and broadcast)?

Thank you.

Author Comment

ID: 18023269
The internal network is /26. The public IP's are /29. The VPN should only be concerned with the internal network addresses, in regards to tunnel initiation.
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Author Comment

ID: 18023278
sorry....wrong board
LVL 77

Accepted Solution

Rob Williams earned 500 total points
ID: 18023294
>>"So you agree that the scenario I described is possible "
If you were to adjust so that they were on the same subnet, you would have a routing conflict. Routers route traffic based on subnets. If they are the same the router will not know to which end of the tunnel the packet is destined, and it will be lost.
You're on the right track :-)
LVL 77

Expert Comment

by:Rob Williams
ID: 18023411
Thanks effincomputers, good luck with it.

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