Raspberry Pi dropping WiFi when ethernet plugged in

I do love my Raspberry Pi! That’s Pi, as in very small computer, not pie as in desert. (I’m diabetic, so please don’t tempt me.) I use these little devices for all kinds of projects.

I’ve recently started using them to test an internal network with a series of routers, with each Pi on a different network. (192.168.11.0/24, 192.168.22.0/24… you get the picture.) To test these, I set static IP addressed on the ethernet connections and then access them with ssh via their dynamic WiFi IPs.

To configure the devices, I would first log in using ssh to the wlan0 interface, configure /etc/network/interfaces with the desired static IP, then plug in the ethernet cable. The problem with this was that as soon as I plugged in the cable, my WiFi connection would drop, causing me to lose all contact with the Pi.

#sudo ifplugd eth0 --kill