[arch-general] systemd-networkd and netctl with multiple interfaces

[Sean Greenslade]

On Wed, Nov 11, 2015 at 09:47:25AM +0100, Bennett Piater wrote:
> Hello!
> I installed Arch on my new Thinkpad T450s over the weekend.
> Everything works well, but I have a question:
> 
> I use systemd-networkd to manage my network interfaces and netctl for
> the connections. I set everything up according to (this)[0] and
> (this)[1] to get automatic activation of wifi via netctl-auto and
> netctl-ifplugd.
> 
> My question is as follows: I use i3wm, and i3status shows *both*
> ethernet and wifi as connected if I plug in the cable while having a
> wifi connection. What does this mean exactly, and how is my traffic routed?

To point out something that other areas of the discussion have ignored:
existing connections.

Say you start out on wifi, and open an ssh connection. Then you plug in
ethernet. The ssh session will remain on the wifi route until it is
closed. There's no way* to make an existing connection "jump ship" from
one route to another. If you were to disable the wifi connection as soon
as the ethernet connection, your ssh session would die.

--Sean


* Technically, this is a lie. Interface teaming / bonding can do this,
but it requires a very special setup and I'm not sure it would work over
wifi. Regardless, it is very difficult to make work properly in most
normal networks.