For testing purposes, we build for an x86 target that can be simulated with QEMU, and runs inside a Docker container. Its Ethernet interface is also simulated, and uses the TUN/TAP interface. You can use this to try the examples or for your own development with Zephyr, without the need to have an actual board connected; you only need to have Docker installed as the Zephyr Docker image handles the emulation for you.

You'll need a TUN/TAP interface (default name is tap0) on your host machine; follow the instructions here to configure your network to provide a suitable networking environment.
Run make build BUILD_ARGS="-b qemu_x86" OVERLAY="-DOVERLAY_CONFIG=overlay-e1000.conf".
- The interface configuration on the simulated machine side is in the file overlay-e1000.conf, and defaults to tap0. You can change this file or specify a different one by changing the OVERLAY_CONFIG argument above.
Once the build succeeds, run make run to run the target. The default Docker configuration is to share /dev/net/tun; if this does not work for you, pass the necessary Docker parameters to make with a DOCKER_ARGS= argument.