In addition to what M02@rt37
From my notes :
Network Address Translation
===========================
Each computer and device within an IP network is assigned a unique IP address that identifies the host.
Because of a shortage of public IPv4 addresses, most of these IP addresses are private and not routable anywhere outside of the private company network.
RFC 1918 defines the private IP addresses you can use internally that should not be advertised:
10.0.0.0 through 10.255.255.255
172.16.0.0 through 172.31.255.255
192.168.0.0 through 192.168.255.255
One of the main functions of Network Address Translation (NAT) is to enable private IP networks to connect to the Internet.
NAT replaces a private IP address with a public IP address, translating the private addresses in the internal private network into legal,
routable addresses that can be used on the public Internet.
In this way, NAT conserves public addresses because it can be configured to advertise at a minimum only one public address for the entire network to the outside world.
Other functions of NAT include:
Security-Keeping internal IP addresses hidden discourages direct attacks.
IP routing solutions-Overlapping IP addresses are not a problem when you use NAT.
Flexibility-You can change internal IP addressing schemes without affecting the public addresses available externally;
for example, for a server accessible to the Internet, you can maintain a fixed IP address for Internet use, but internally, you can change the server address.
Translating between IPv4 and IPv6 (Routed mode only)-If you want to connect an IPv6 network to an IPv4 network, NAT lets you translate between the two types of addresses.
Static network address translation SNAT.
SNAT maps unregistered IP addresses using 1 to 1 network address translation to match up with registered IP addresses. It is particularly useful when a device needs to be accessible from outside the network.
Dynamic network address translation DNAT.
This form of NAT selects a target from a group of registered IP addresses and maps an unregistered IP address to the registered version.
Reverse network address translation RNAT.
RNAT allows users to connect to themselves using the internet or public network.
Overloading network address translation NAT.
This is also known as NAT overload, port-level multiplexed NAT, single address NAT, or port address translation (PAT).
This form of dynamic NAT uses different ports to map multiple private, local, unregistered IP addresses to a single registered IP address and distinguish which traffic belongs to which NAT IP address. In terms of port address translation vs network address translation, PAT is often most cost-effective when many users are connected to the internet through just one public IP address.
Overlapping network address translation NAT.
Overlapping NAT can happen either when two organizations whose networks both use RFC 1918 IP addresses merge,
or when registered IP addresses are assigned to multiple devices or otherwise in use on more than one internal network.
In both cases, the networks need to communicate, and the organization(s) use overlapping NAT to achieve this without readdressing all devices.
