Red Hat Bugzilla – Bug 463340
NM routed traffic over the slower of two interfaces.
Last modified: 2015-01-04 17:30:38 EST
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..
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)
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.