Need for NAT & Its Pros and Cons

NAT is Network Address Translation, For basic details about it refer the link NAT Overview
NEED for NAT

The major need for introducing NAT was exhausting IP Address, though it also got the Identity of Securing the Internal Private Network. The Private IP Address was hidden inside Th outside Public Address.

It Also Served the purpose of Private IP Address not routable into Internet, so they are translated to Public IP through NATing 

Advantages of NAT

•  Securing the Internal Private IP from outside world. So that Attacker wont be able to track Internal IP.

• Reusing Private IPs again and again at different local networks can be possible because of NAT. Hence Preserving depletion of IPv4 Addresses

• NAT helps in preventing internal Address Change if you change the Service Provider.

Disadvantages Of  NAT

• NAT  is a processor and memory resource consuming technology, since NAT need to translate IPv4 addresses for all incoming and outgoing IPv4 datagrams and to keep the translation details in memory.

• NAT  may cause delay in IPv4 communication.

• NAT cause loss of end-device to end-device IP traceability.

• Also Some Applications and Technologies will not function as expected in NAT.

Host A-----Inside IP Address----NAT----Outside IP Address-----Internet

Host A----Private (Local IP)-----NAT-----Public (Global IP)--------Internet