The Ethernet.h library is the standard tool for connecting Arduino boards to the internet or local networks using wired Ethernet shields or modules.
The easiest way to get the library is through the built-in Arduino Library Manager : ethernet.h arduino download
While the Ethernet.h library is often with the Arduino IDE, you may need to download it manually if you are using a portable installation, a third-party IDE like PlatformIO, or if you want the latest version with improved hardware support. Method 1: Using the Library Manager (Recommended) The Ethernet