Can You Get a User\'s Local LAN IP Address with JavaScript?

Can You Retrieve a User's Local LAN IP Address Via JavaScript?

Many initially assume that retrieving a user's local LAN IP address through JavaScript is impossible. However, this is not necessarily the case.

The question stems from a desire to display the user's LAN IP address on a web page, similar to the information provided on WhatsMyIP.org. While some may question the need for this information, for some users, such as computer consultants, it can be a valuable tool for network analysis.

In the past, Java applets were commonly used to obtain this information. However, due to the increased security concerns surrounding applets, developers have sought alternative solutions.

Enter WebRTC

The WebRTC (Web Real-Time Communication) extension of HTML5 provides a possible solution. It allows JavaScript to query the local client IP address. A proof of concept can be found at Net.IPCalf.com.

This feature, apparently intentional, enables the retrieval of the user's LAN IP address. However, it is important to note that this behavior could change in the future, so caution should be exercised when implementing it. Nevertheless, for the purpose of displaying leaked information to the user, it appears to be a suitable solution.

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