How to untag a VLAN

Create a test VLAN with OpenWRT like so:

Assuming your eth0 is enp0s25 like it is on my system.

sudo ip link add link enp0s25 name eth0.1 type vlan id 1
sudo ip link set dev eth0.1 up
sudo dhcpcd eth0.1

You can inspect the VLAN ID with sudo tcpdump -n -e -vv -ttt -i enp0s25 vlan or with wireshark.