Private IP address


There are two types of IP address, called Private IP address and Public IP address. So, what’s the differences of these two? I’ll explain about it!

Private IP address and Public IP address

Public IP address is allocated to the NIC which is connected into Internet, and ICNN manages Public IP address.


Now, you are reading this “Tech Power Blog” by connecting your PC to the Internet, so your device has Public IP address.


On the other hand, Private IP address is uniquely assigned within an organization, like home, office, etc. When we use the Private IP address, we don’t have to apply to the organization like IPNIC. Nonetheless, if the IP address isn’t unique within an group, connection can’t work well, so Private IP address have to be assigned uniquely within an organization.


If the device which only have Private IP address, packet have to be relayed by the device that have Global IP address.


Exchanging Private IP address into Global IP address is called NAT. When packet is sent from LAN to Internet, NAT exchange sender IP address.


On the other hand, when LAN receive the packet from Internet, NAT exchange destination IP address. Thanks for this technology, the client in LAN can secure Internet communication.


NAPT is the abbreviation of “Network Address Port Translation”, and as this words express, NAPT can exchange Port Number in addition to IP address.


For example, if you want two devices, which have Private IP address, to communicate through Internet, router can distinguish each other by checking the Port Number. So you can save the Global IP address.


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