PR: Linksys is 192.168.1.1, and you leave user name blank and use admin for the password. Different brands are different, what you said applies to a D-Link.
NAT = network address translation. It's enabled if the router works.
Look around for "discard WAN ping" or something similar. That makes you essentially invisible from the outside and should be enabled.
For a test, go to
https://www.grc.com/x/ne.dll?bh0bkyd2