Hello Frederic,
You can use the built in client on OS X, it uses a PPTP VPN.
On the RV180 admin page go to VPN >> IPSec >> VPN Users. Check the enable PPTP server option and enter the IP address range you want to use for the remote users and click save. You can use the same range as your local network if you want.
Then you can go to the VPN Client Settings Table on the same page and add a user, making sure to select enabled and pptp for the protocol type.
You don't have to open up anything on the firewall. At this point you should be able to configure a VPN connection with the built-in OS X client using the WAN IP of the RV180 as the server address.
Let me know how that goes,
Christopher Ebert
Network Support Engineer - Cisco Small Business Support Center
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