Different Types of Home-Based Routers Exist, and those routers provide NAT Feature as well e.g; and most of them are Port Restricted.

Q-1 : What kind of Base Softwares Manufactures use to develop NAT Functionality ?

Q-2 : Is that Technology Proprietary ? Or some Open-Source used to develop that e.g; Firehol ?

Q-3 : I am looking for a software which works exactly like a NAT,and by doing very basic configuration it should work either Symmetric NAT, Port Restricted NAT or Address Restricted NAT ? So that I can test some of my Network Application which are dependent on NAT via this way on same PC ? e.g; I can test my developed ICE Algorithms