Network Address Translation

Network Address Translation(NAT) is a type of tool that is used forhiding internal network addresses and it enables with several endpoints within a LAN where same(external) IP address can be shared.NAT can actually be referred as network and port translation(NAPT).

In NAT outgoing IP headers are getting changed from private LAN address to routers global IP whereas in NAPT,TCP/UDP headers are getting converted which allows several users to share router global IP address at a time.Machines that doesn’t use internet are assigned with local address on intranet instead of taking IP address.NATs is also useful for security of LAN,that helps in making internal IP address less accessable from public internet,thus all the attacks against network are focussed at NAT router itself.This provides easy security because we need to protect only one point i.e router.

This also simplifies network management because in order to change ISP,only external router configuration need to be changed.The internal network and addressing scheme shouldn’t be touched.Different types of NAT are available such as Full Cone NAT where the request for same internal IP address and port are mapped to same external IP address and port.

Any packet to internal host can be send by external host through mapped external address.Another type of NAT is Restricted Cone NAT where likewise in Full Cone NAT all request from internal IP address and port are mapped to same external IP address and port but here the difference is that an external host(with IP address X) can send pocket to internal host only if internal host had sent packet to IP address X.Next type is Port Restricted Cone which is like Restricted Cone NAT,but in this case port numbers are also included.here external host(IP address X and source port P) can send packet to internal host only if internal host has sent pocke to IP address X and port P.thus,enables sharing of external IP address..

The last type is symmetric NAT where all requests from same internal IP address and port, to a specific destination IP address and port are mapped to same external IP address and port.If same host tries to send packet to different destination with same address and port,different mapping should be used.Only external host that recieves a pocket can send UDP packet back to internal host.along with all above mentioned advantages it has certain disadvantages also such as it violates the fundamental semantic of IP address,that is globally reachable point for communication.

If a NAT is introduced,it becomes very difficult to call in a network such as in a house with multiple phones.this design is used for VOIP.Even if today IPV6 and its expanded address space are being used and there are enough IP address.Still,there would be need for NAT as it is cheap,easy and most efficient solution.