I am working on creating a mesh network setup using the batman-adv routing protocol and a couple of Pis. One of my issues right now is turning one of those Pi nodes into a gateway node, which is connected to the outside internet. In order to do that, I use both the internal wifi adapter and an external USB adapter. However, the internal wifi adapter (wlan0) needs to be utilized by the batman-adv setup. How do I set up the Pi to therefore only utilize my external USB adapter to connect to the internet? Right now when I connect to a network through the Pi, it always defaults through the built in wifi card.
With every network management system, no matter if it is ifupdown, dhcpcd, systemd-networkd or Networkmanager (not supported with Raspbian), you are able to configure what interface (wlan0 or wlan1) is connected to what subnet. You don't tell us anything about your network environment so I can only suggest to look at your network setup how it manages to connect an interface to a subnet. In addition you can try to disable wlan0 completely. Set this option in