What are NAT and PAT?  Describe these technologies.

What will be an ideal response?

NAT is a method of converting multiple real, routable external IP addresses to special ranges of internal IP addresses, usually on a one-to-one basis; that is, one external valid address directly maps to one assigned internal address.  A related approach, called port-address translation (PAT), converts a single real, valid, external IP address to special ranges of internal IP addresses-that is, a one-to-many approach in which one address is mapped dynamically to a range of internal addresses by adding a unique port number when traffic leaves the private network and is placed on the public network.