Networking :: Trying To Make Sense Of Linksys Router User Guide

After I installed a gigabit router, I could not access my nfs server anymore; I tried with the previous physical set-up and all was OK so clearly it is the new router that is the disturbing factor. After some (and then some) experimenting, it would appear that the following specific feature needs to be enabled: Filter Internet NAT Redirection This feature uses port forwarding to block access to local servers from local networked computers. Select this feature to filter Internet NAT redirection. It is not selected by default.

The reason I had simply looked over it is that I did not see how internet nat redirection could be related to the local network. As I read the details, it became clear that it really is but it also raised new questions. Have I now allowed just anyone on the internet to access to my nfs server? Because the description is not very clear either as it mentions both internet and local network. And what is that odd terminology? Filtering allows access, not filtering does not - that seems like the world upside down ...