How does Linux determine which network interface to use, when both are connected to the same network?
Note that this isn't a question on routing. I'm familiar with how that works. This is if, say, I have my laptop connected to my wireless router through both my ethernet card and my wireless card, or if I have two ethernet cards both connected to the same router.
I can say from experience that in my case, my laptop seems to favor the ethernet card (eth0) over the wireless (eth1--I know that's not a typical name for a wireless interface, but that's what I have), but I was wondering, how does it decide that? If it just picks from the lowest numbered interface, what if the two choices are, say, eth0 and wlan0?
Edit: @Nils has pointed out that this is still a matter of routing, and the routing table provides the answer (see his answer). This still leaves my original question, but in a different form. What determines the order of entries in the routing table in Linux? For example, here is my routing table while connected to both interfaces:
Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 0.0.0.0 192.168.4.1 0.0.0.0 UG 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 192.168.4.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 192.168.4.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
It's clear that eth0 is higher priority in the table than eth1 for destinations in the local network, but is that decided in Linux from link latency, link throughput, even the interface name, or what? (The same question could go for why eth0 is the interface for the default route.)