On a home private network, the router would have a private IP address something like this 192.168.0.1. On the home network there are 5 computers. Each has a local IP address 192.168.0.xx e.g. 192.168.0.2 – 192.168.0.6. But the computers themselves do not have a public IP, only the router does. So would it be possible for someone from an outside network to send a file to one specific computer in my home network? Like if they know the MAC address of the device.
And how is it that emails can reach e.g. outlook application installed on one computer with one IP address, but still be accessed from another computer with a completely different IP address.
In: 5
Your router is using something called Network Address Translation (NAT). NAT allows the router to hide your personal network (private) IP addresses and dynamically creates tables of what device IPs requested certain services like a google request (port 443) or an FTP request (port 21). When they exit the router to the internet your router appends its public IP address instead of the internal network IP address. When information inbound to the router comes from the internet it strips the public address, looks up the port number it assigned and combines it with the corresponding internal IP address.
*edit: And no, unless your router has some severe and malicious security flaw, it is not possible for an external host to communicate directly with the private IP in your network.
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