Public IP addresses
A public IP address is an IP address that is assigned to a network devices, host and servers to allow direct access to the Internet. Different type of servers like a web server, email server and any server device directly accessible from the Internet are using public IP addresses. A public IP address is globally unique, and can only be assigned to a unique device. Each and every device that’s accessing the internet is using a unique IP address. Public IP addresses are required for any publicly accessible network hardware; like for your home router as well as for the servers that host websites.
Public IPv4 addresses are addresses which are globally routed between different ISPs. However, some IPv4 addresses can’t be used on the Internet. These addresses are called private addresses. These addresses are used for internal hosts on most of the organization.
Private IP addresses
In the mid-1990s private IPv4 addresses were introduced because of the reduction of IPv4 address space. Private IPv4 addresses are not unique and can be used by an internal network. These addresses are allocated to organizations for their own private network. The computers at your home, your tablets, smartphones, network printer; and the computers within organizations are generally assigned private IP addresses.
When a computer is assigned a private IP address, the local computer and devices can see can see this computer through its private IP address. But, the devices exist outside of your private network cannot directly communicate via the private IP address, however, uses router’s public IP addresses, devices outside a private network can communicate. To allow direct access to a local device which is assigned a private IP address, a Network Address Translator (NAT) should be used. The range of private IP address is following for all three classes.
10.0.0.0 /8 or 10.0.0.0 to 10.255.255.255
172.16.0.0 /12 or 172.16.0.0 to 172.31.255.255
192.168.0.0 /16 or 192.168.0.0 to 192.168.255.255
It is important that the above mention blocks are not allowed on the Internet and must be discarded by Internet routers.