Traffic is relayed when WiFi and Eth are enabled at the same time

[fernandoenzo]

Describe the problem
I have a network set up with NetBird with multiple devices located in two houses that I own. The issue I'm facing is that one of the devices is a laptop running Debian 11, and sometimes I connect it via Ethernet and other times I use WiFi. I have noticed that when I connect it via Ethernet while also having WiFi connected, NetBird makes it connect to the other devices using "traffic relayed" instead of P2P. However, if I disconnect the WiFi and only use the Ethernet cable, the traffic is P2P, and the same happens if I only use WiFi and disconnect the Ethernet cable. This doesn't make sense to me because when both devices are connected, the Linux route table (ip r) shows that the Ethernet device has priority (lower metric) over WiFi, so the second device shouldn't interfere at all.

This error occurs to me whether I use the public Netbird server or a personal one that I have set up.

To Reproduce
Steps to reproduce the behavior:

1. Connect both WiFi and Ethernet at the same time, so both of them have one IP on your local network
2. Do netbird status --detail to see how EVERY single device is connected to yours by Relaying traffic, instead of P2P

Expected behavior
Traffic should be P2P, as it is when only one device (either Eth or WiFi) is enabled.

[fernandoenzo]

Could it be related to this other bug? And if so, is there any possibility of fixing it on the Netbird side, as it doesn't seem like they plan to fix this major bug from the Pion ICE side? (look at the year it was reported)

[mlsmaycon]

Hello @fernandoenzo sorry for the delay in replying. Some wireless routers don't allow lateral connection (to local hosts) on WIFI connections. That leads me to believe that the issue is related to how the OS handles routing the traffic to the local network.

Can you run a test on your local setup?

Edit the client.json file (/etc/netbird/client.json or c:\programdata\netbird\client.json) and add the wireless interface name into the list of blacklisted interfaces?

[fernandoenzo]

Hello! Thank you for your reply.
I tried what you said (I'm using Debian 11 btw) and nothing changed. I mean: traffic is still being relayed. It's like it's not taking into account that I blacklisted the Wireless interface.

Nonetheless, if this option (putting the interfaces on a blacklist) were to work, wouldn't that leave me without a connection to Netbird if I unplug my laptop from the wired network?

[fernandoenzo]

Any news here?