Public IP vs. Private IP: Essential Concepts for Industrial Network Operations

I. Why Does Your Device Have Two IP Addresses?

In industrial network operations, a common observation is this: when an engineer checks the IP configuration on-site, they see an address like 192.168.1.100. However, when they query their public IP online, the displayed address is completely different, and its location may even be in another city.

Both addresses are considered "your IP," but they play entirely different roles. Understanding their distinction is a prerequisite for troubleshooting issues related to remote access, VPN connections, and device cloud connectivity.

II. Private IP: The "Badge" Within the Local Network

A private IP address is assigned by a router to devices within a local network and is only valid internally. It's like an employee ID badge – it identifies you within the company, but holds no meaning outside.

Common Private IP Address Ranges

Key Characteristics: Private IPs are non-routable on the public internet; external devices cannot directly reach yours via this address. Also, different local networks can use the same private IP ranges without conflict.

III. Public IP: The "ID Card" on the Internet

A public IP is assigned by an Internet Service Provider (ISP) and uniquely identifies your network's access point on the global internet. It's like a national ID card – unique worldwide and recognizable from anywhere.

Key Characteristics: A public IP is reachable from any device on the internet, making it a prerequisite for remote access, hosting servers, and connecting devices to the cloud. It can also be used to roughly locate the device's city and ISP.

IV. NAT: The "Translator" for Internal Devices to Access the Internet

If private IPs can't directly access the internet, how do devices connect? The answer lies in NAT (Network Address Translation).

The core function of NAT is to allow multiple devices on a private network to share a single public IP for internet access. When an internal device initiates an outbound connection, the router "translates" its private IP to its public IP for the outgoing data. When the external data returns, the router reverses the process, forwarding it to the correct internal device based on its stored records.

In industrial settings, the industrial router typically acts as both the router and the 4G/5G cellular modem, serving as the primary NAT gateway. Field devices connect to it via wired or Wi-Fi, and the router handles all address translation and data backhaul over the cellular network.

Why do ISPs do this? The supply of IPv4 addresses is limited (approximately 4.3 billion total), while the number of connected devices worldwide far exceeds this. By using NAT, ISPs can serve thousands of households with far fewer public IPs, alleviating the pressure of address exhaustion. This is the origin of CGNAT.

V. How to Determine If You Have a Public or Private IP

Method 1: Check Your Device's IP Range

Open the command prompt (cmd) and type ipconfig. Look for your IPv4 address. If it falls within 10.x.x.x, 172.16.x.x to 172.31.x.x, or 192.168.x.x, it's a private IP.

Method 2: The Comparison Method

1. Open a web browser and go to an IP lookup website to find your public IP address.

2. Compare this public IP with the IP you found in ipconfig.

   • If they are different, your device is behind NAT (most common scenario).

   • If they are identical, your device is directly using a public IP.

Method 3: Check Your Router's WAN IP

Log in to your router's management interface and find the WAN port status. The WAN IP is the address your ISP has assigned to your connection. If this WAN IP also starts with 10., 172.16-31., or 192.168., then even your ISP has placed you in a "Carrier-Grade NAT" environment.

VI. The Value of a Public IP in Industrial Scenarios

For most daily office tasks and general internet use, a private IP is sufficient. However, a public IP is necessary for the following industrial use cases:

• Remote Device Access: Engineers in different locations can directly access on-site industrial routers, PLCs, or HMIs via a public IP for program downloads and diagnostics.

• VPN Connections: Multiple factory sites can establish IPsec/OpenVPN tunnels over public IPs to create secure, interconnected networks across geographic locations.

• Video Surveillance Backhaul: Live surveillance feeds can be pushed directly from the field to a central monitoring platform using a public IP.

• Device Cloud Connectivity: Industrial equipment can maintain stable, persistent connections to cloud management platforms via public IPs.

If your project requires a public IP, you can usually request one directly from your ISP. Some regions offer dynamic public IPs for free with a simple phone call, while others may charge a small fee or require an upgrade to a business plan.

VII. Conclusion

Public and private IPs are fundamental concepts in networking. A public IP is the global identifier on the internet, while a private IP is the local identifier within a LAN. They work together through NAT technology.

For on-site industrial operations staff, understanding IP addressing and being able to quickly identify the network environment helps ensure more efficient troubleshooting and deployment, reducing misconfigurations and delays caused by a misunderstanding of network architecture.