Allow 2 different subnets to have access to the internet but not each other

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http://serverfault.com – How would I go about getting say and to both have access to the same internet, but not see each other. My Topology can change to make this happen. Currently I have a router/gateway which connects to the internet via LAN cable. This router at the moment is basically stock setup, apart from a static IP (, which is what my 10.0.0.x subnet uses to connect to the net... but this doesn't work for the other subnet. (HowTos)