Internal IP Addresses
For an internal network IP address, a router or another DHCP server controls the IP address and uses a completely different system than the IANA system that assigns IP addresses at the Internet level. This means that IP addresses for individual devices are more complicated than the IP addresses assigned to websites and other Internet services.
Servers outside the network will see the IP address assigned to the network router, not to the devices inside the network. For example, the website WhatIsMyIP shows the external IP address that the ISP assigned to the network, not the internal IP address of an individual computer or network device.
From outside the network, the network’s IP address is public, just like the address on the front of a large office building.
Because an IP address is assigned to a specific router by the ISP, that address can be used to identify the network used to commit computer crimes like fraud or transmission of child pornography, although it cannot be used to identify specific devices within the network.
For this reason, it is very important to make sure that personal wireless routers are secured with a password. If there is no security on the wireless router, anyone can use the router to commit a crime using that network without ever entering the building, making it impossible to trace the machine that was used to commit the crime.
Any data transmission over the Internet will include the IP address of the router, making it relatively easy to identify what network was used. No one wants the police knocking at their door for a crime they did not commit.