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why do we have private network addresses

Why wouldn't you just skip the private address altogether and assign a public one if the host needs to connect to a network? Because there are not enough public addresses in IP version 4 to give every possible Internet connected device a unique address. This is why IP version 6 uses more bits for the address range and has more addresses. Private address blocks are not supposed to be routable over the public Internet (this is what makes them "private"). Since there are only 3 private blocks with a relatively small number of addresses within them, they are guaranteed to be reused by anyone and everyone who has a private network (private addresses ONLY need to be unquie within a private network, but another private network might reuse the same addresses). So you cannot just put the private address blocks "out there" - they will conflict with someone else who is using the same block elsewhere.

So this is why NAT is needed. To directly answer your last statement, if you have enough public addresses available to you, then you don't need NAT to send and receive traffic. NAT isn't necessary for this reason if you aren't trying to "save" IP addresses. For completeness, I'll say this: some people rely on the following side effects of NAT for security reasons and that could be a reason to elect to use it even if you do have enough public IP addresses:
since outgoing traffic from NAT looks like to external systems that it comes from the router's IP, this hides details of the machines behind the NAT from external systems, i. e. how many machines, their private IPs, etc. A private IP address is a non-Internet facing on an internal network. Private IP addresses are provided by network devices, such as routers, using network address translation ( ).

Originally it was thought that 's IP addressing system -- yielding 4,294,967,296 theoretical IP addresses -- would be adequate for all purposes. However, as the Internet grew it became apparent that something had to fill the gap between IPv4 and a future system (which would turn out to be ) that would take time to develop and implement. Private IP addressing and NAT fill that gap with the private IP range. Private IP addressing uses addresses from the class C range reserved for NAT (192. 168. 0. 0 в 192. 168. 255. 255). Private addresses can be assigned by the router using or be manually set, after which those addresses can communicate with one another through the router. Private IP addresses can only be guaranteed unique to an internal network, excepting conflicts.

If a directly connected computer does not have a static IP address assigned, even assigning a private IP address manually will not enable communication. Private IP addresses cannot be directly contacted over the Internet as a computer with a public IP address can. This situation affords an extra layer of security: A network NAT device communicates with the Internet using its public IP address from an and checks to see if any incoming data was requested by one of the private IP-assigned computers. If so, it is directed to that computer; if not it is typically discarded. Another benefit of using NAT, for those who do tend to have incoming requests -- like websites, file and game servers в is the ability to quickly switch servers in the event of a crash, as the incoming traffic can all be forwarded to a back-up server very easily.

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