What is a private IP address?



The private IP addresses are the reserved IP address blocks that cannot be routed through the internet. Since private IP addresses are only intended to be used in private networks, they are not globally unique. The private IP address must be unique within its network (usually LAN) so that there is no conflict between two computers within its network. Due to scarce nature of IPv4 Address (i.e. approximately 4 billion IP addresses), IANA reserved private IP address blocks so that they can be used by any organization without registering them with IANA. The private IP address block can be used in homes, small businesses, or even medium and large enterprises to create their own network. Computing devices with a private IP address cannot be directly accessed from the Internet unless NAT (Network Address Translation) is used. The advanced network planning techniques have also enabled network planners to use same private IP address within different private networks thus allowing them to save valuable IP address space. A private address may also be referred to as a local IP address. It also enables to hide the identity of the users over the Internet.

ClassReserved Address SpaceNumber of IP addresses
Class A 10.0.0.0 up to 10.255.255.255 16,777,216
Class B 172.16.0.0 up to 172.31.255.255 1,048,576
Class C 192.168.0.0 up to 192.168.255.25565,536

The ranges of private IP addresses belong to different IP Class. It helps to determine the total number of possible IP addresses that can be assigned from a reserved address space. It also allows planning for reusing those IP addresses within different private networks without routing these IPs over the Internet.

Significance of Private IP Addresses in Modern Networks

The private IP address space enables to hide your whole private network behind the router and saves public IP address space. The NAT or network address translation technique enables a device residing in private network to provide services to the Internet. It is implemented by the router that allows the exchange of messages between private and public (Internet) networks. We have the very limited pool of public or internet IP addresses within IPv4 address space as IPv4 is limited to 32 bits. We cannot assign a new public IP address to every single device in the world as there are more than 232 or roughly 4 billion addresses. The devices residing in a private address can still access the Internet if the private network is connected to the Internet via a router. A public IP address is assigned to the router, and all computers contained within the private network will share same public IP address of the router when accessing the Internet. As more and more devices are connected to the Internet, private IP address blocks allow enterprises to create the private networks without consuming globally unique public IP addresses. The router implements the NAT (Network Address Translation) functionality to complete the communication procedures between two devices from two different private networks that may have same or different private IP address. The NAT simply takes a private IP address translates it into a public IP address (of a router) for use over the internet.

What Private IP Address can I use on my network?

What range of private IP addresses one must use while setting up a private network?. Should this range be from Class A, Class B or Class C block? It totally depends on the number of networks you need to create and the number of devices you need to connect to the network. The corporate networks usually make use of Class A addressing schemes (10.x.x.x). It allows the network planner to configure maximum possible hosts with virtually limitless network planning schemes. Each Class C network can have up to 254 hosts or devices connected to it. By using class A or B network, it enables for easy growth or expansion of the network without impacting current operational infrastructure to meet future requirements. Small networks or home networks usually opt for the Class C private IP address (192.x.x.x). Class C IP address can be configured quickly with ease and most routers designed for residential use have default IP address of (192.0.x.x or 192.1.x.x). It allows configuring a small network with up to 254 devices. It may include PCs, Laptop, Smartphones, Tablets and other smart home devices.

Automatic Private IP Addressing (APIPA)

The Internet Assigned Number Authority (IANA) has allocated a new private IP address space. The range for APIPA address space is from 169.254.0.1 up to 169.254.255.254. It is commonly known as automatic private IP addressing scheme. It allows the clients with latest operating systems to automatically configure IP address from this address space. It enables the devices to operate smoothly within a private network even if you forget to assign an IP manually or no IP is assigned by dynamic host configuration mechanism.

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