AQA Computer Science A Level

Using Private IP Addressing
By Admin - June 21, 2020, 4:55 p.m.
Last Edit - June 24, 2020, 1:41 p.m.

IPv4 has many obvious limitations, but its 32bit nature is the main one. This severely limits the number of addresses available, but this was thought about many years ago and to combat this Public and Private IP ranges were set

Private IP addresses are used internally only, each device connected to the network will get a private IP address. A network will have a public IP to access the internet and externally. Private IP's will not route to any public address. Every IP address not in the private ranges are therefore public.

The private IP ranges are:

The benefits of this are:

How is this used

The public IP address for my network is, this is the only public IP for my network and it connects to the router. My router also has a private IP of, a private IP is given to every device connected to my network. The Network ID is 192.168.0 and the Host ID is 1.

I'm writing this on my phone from, this blogging platform is hosted on a raspberry pi with the IP I have many other devices connected but they all use the same Network ID and a different Host ID.

The key to this is Network Address Translation, this is the process of swapping the Private IP of the sending device to the Public IP of the router on the outward journey (The router will record all translations). Then on the inward journey the Public IP of the router is swapped to the Private IP of the sending device. It will know this by checking the translations record for the outward journey.

What can you do?