17.8. Troubleshooting IPsec Site to Site VPN

Check the SAD. Check the Security Association Database (SAD) under Diagnostics. You need to have an entry here for the connection. If you do not, you don't have something configured properly.

Verify Suitable IP Subnets

First make sure the two subnets you are trying to connect don't lie within the same address space. i.e. if both sides are, the connection will not work. Same goes if one side is and the other is, or similar, the latter lies in the subnet of the former.

If they are within the same address space, you'll need to change one side or the other. There is no way to set up a site to site IPsec VPN with any product when this is the case.