I had my laptop plugged into my router via gigabit ethernet, and started scp'ing ~10GB of data to another machine. At some point, NM realised it could auth with my access point, and get to the same host via wireless.. $ route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.0.0 * 255.255.0.0 U 0 0 0 wlan0 192.168.0.0 * 255.255.0.0 U 0 0 0 eth0 default firewall.kernel 0.0.0.0 UG 0 0 0 eth0 At this point, the scp slowed to a crawl (measured in KB/s rather than MB/s) When I did an ifdown wlan0, the speed went back up again. If we have a routable interface via ethernet, why bother bringing up wireless unless we ask for it? (especially if they both end up with the same netmask)
+1. See also https://bugzilla.redhat.com/show_bug.cgi?id=454955 for similar request / rationale.
This should be fixed, NM will now use metrics with device routes so that faster devices (Ethernet > Wifi > Mobile Broadband) will have a lower metric, and thus be more preferred.