Why Private IP address can not travel over public infrastructure ?

Hello Ankit,

Though Private IP address spaces were originally defined in an effort to delay IPv4 address exhaustion. Private IP addressing is most commonly used for end users since it is not possible to assign Public IP's to each and every internet user in the world which may lead to IP address exhaustion. So instead of assigning Public IP's we could assign Private IP addresses to end users. Refer to the design:

Lets Consider R1, R2 and R3 are home internet routers which provides the same private address space for the end users which could save alot of Private IP's. Since the private IPv4 address space is relatively small, many private IPv4 networks use the same address space. This can create a problem when merging such networks, namely the duplication of addresses on multiple devices. In this case, networks or hosts must be renumbered, often a time-consuming task, or a network address translator must be placed between the networks to masquerade the duplicated addresses. Thus, IP packets addressed from them cannot be transmitted through the public Internet, and so if such a private network needs to connect to the Internet, it must do so via a network address translator (NAT) gateway, or a proxy server.

I hope it helped. Please feel free to ask.

Thanks