How to prioritize Wifi over Ethernet

Question

Scenario

• wlan0 is configured to connect to an internet-connected router and gets an IP via DHCP
• eth0 is set to a static IP (via /etc/dhcpcd.conf, different net than wlan0) and connected to a net with no router, gateway or DHCP server.

Goal

I want to talk to devices connected to eth0 while maintaining internet connectivity through wlan0.

Problem

As soon as a cable is connected, the internet connection goes away. The default route is always set to the non-existent gateway of eth0. Manually setting the default route to the gateway of wlan0 works, but I don't want to hardcode this, as wlan0 is connected to different networks with different IPs.

Answer 1

As Ethernet isn't connected to internet you can disable this by adding the following at the bottom of :- /etc/dhcpcd.conf

interface eth0
  nogateway

Answer 2

Change the metric of the interfaces. In /etc/dhcpcd.conf the following setting works:

interface eth0
metric 300

interface wlan0
metric 200

Now the gateway assigned to wlan0 via DHCP will always be the default route (if present).

Answer 3

When I was trying the 2 posts out I added this:

interface eth0
nogateway

This did not work for me then I tried the next solution:

interface eth0 metric 300

interface wlan0 metric 200

But left the nogateway entry inside the /etc/dhcpcd.conf file, which deactivated the WLAN Adapter when I rebooted. I don't know why, if you choose the metric solution, make sure you remove also the nogateway entry.