NAT Playlist: https://www.youtube.com/playlist?list=PLDzveA55I0_gGGIxKOH3XUbV331J8uLU6

http://blog.ine.com/2008/02/15/the-inside-and-outside-of-nat/

http://www.astorinonetworks.com/2011/08/16/the-inside-outside-of-nat-for-overlapping-networks/

https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/13770-1.html

https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/13774-3.html

IP nat inside source (Normal NAT for Internet) 
o Translates the source of the IP packets when traveling from inside to outside
o Translates the destination of the IP packets when traveling from outside to inside


IP nat outside source (Useful for overlapping subnets)
o Translates the source of the IP packets when traveling from outside to inside
o Translates the destination of the IP packets when traveling inside to outside