Understanding the Connection Between Private IP Addresses, MAC Addresses, and Public IP Addresses

Have you ever wondered if it is possible to find a public IP address based on a private IP address or a MAC address? In this article, we will explore why such direct correlations do not exist and how IP addresses operate within a networked environment. We will also discuss how public IP addresses are assigned and managed within a local network.

Why You Can't Find a Public IP Address from a Private IP Address

Private IP addresses are defined by the Internet Assigned Numbers Authority (IANA) through RFC 1918 for use within local networks. These addresses are 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to 192.168.255.255. Since these addresses are not routable on the internet, they are not visible outside the local network. Therefore, it is impossible to derive a public IP address from a private IP address.

Why You Can't Find a Public IP Address from a MAC Address

A MAC (Media Access Control) address is a hardware identifier assigned to network interfaces for communication on a local network. Operating at the data link layer, the MAC address is unique to each device on a local network. However, it does not offer any information about the public IP address assigned to that device. The public IP address is managed by the router and is used for routing traffic across the internet.

How Public IP Addresses Are Assigned

Devices connected to a local network will usually access the internet through a router that has a public IP address. This public IP address is used for routing data to the internet. The router implements Network Address Translation (NAT) to manage the mapping between private IP addresses and a single public IP address. This allows several devices to share the same public IP address.

To illustrate, imagine a small office with multiple computers, each with a private IP address. All these devices are connected to a router, which has a single public IP address assigned by the ISP. Through NAT, the router ensures that each private IP address is correctly mapped to the public IP address when data is sent out to the internet.

Conclusion: Finding Public IP Addresses

If you need to determine the public IP address of a device, you can check it directly from the device using online services like Alternatively, if you have administrative access to the network, you can access the router’s configuration page to view the public IP address.

Why MAC Addresses Don't Help Identify Public IP Addresses

While the MAC address is visible on the local network segment, trying to match it to a private IP address by interrogating the 'arp' (Address Resolution Protocol) table is not practical. The 'arp' table is local to a machine, so you would need to do this on every computer on the network segment. Additionally, due to the large number of devices around the world that might share the same private IP address, the chances of finding a unique public IP address based on a MAC or private IP address are virtually non-existent.

Take this laptop as an example. It has an IP address of 192.168.1.201, and there are countless other devices worldwide with the same IP address. Therefore, knowing this IP address would not help in determining the public IP address, especially since the public IP address used by my ADSL modem in the garage is managed by the ISP and changes regularly.

In summary, if you need to know a public IP address, it's best to check it directly from the device or access the router’s configuration page, as obtaining it from a private IP address or MAC address is not feasible.