15.04: no route when connected to both WiFi and Ethernet

[Jason Gerard DeRose]

Steps to reproduce
===============

1) Enable both a WiFi connection and plug into Ethernet
2) Test your network connectivity or run `route`

Expected results
=============

NetworkManager should prefer the wired connection over the WiFi connection, and `route` should return something like this:

$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 10.17.75.1 0.0.0.0 UG 1024 0 0 wlan0
10.17.75.0 * 255.255.255.0 U 0 0 0 wlan0
link-local * 255.255.0.0 U 1000 0 0 wlan0

(To get the above results on Vivid, I had to unplug my Ethernet.)

Actual results
===========

`route` will produce no results and your connectivity will be broken

Work-arounds
===========

As soon as you disable either the WiFi or unplug from Ethernet, you will again have a route and your network connectivity will work. This is a regression from Trusty and Utopic.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: network-manager 0.9.10.0-4ubuntu15.1
ProcVersionSignature: Ubuntu 3.19.0-15.15-generic 3.19.3
Uname: Linux 3.19.0-15-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Apr 30 16:00:09 2015
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IpRoute:
 default via 10.17.75.1 dev wlan0 proto static metric 1024
 10.17.75.0/24 dev wlan0 proto kernel scope link src 10.17.75.247
 169.254.0.0/16 dev wlan0 scope link metric 1000
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
 WimaxEnabled=true
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-con:
 NAME UUID TYPE TIMESTAMP TIMESTAMP-REAL AUTOCONNECT READONLY DBUS-PATH ACTIVE DEVICE STATE ACTIVE-PATH
 Wired connection 1 4ff8582e-2864-4729-877e-52b037de1ee8 802-3-ethernet 1430431120 Thu 30 Apr 2015 03:58:40 PM MDT yes no /org/freedesktop/NetworkManager/Settings/1 no -- -- --
 system76_5g 74de1f59-702b-4d15-9803-82b281989bed 802-11-wireless 1430431008 Thu 30 Apr 2015 03:56:48 PM MDT yes no /org/freedesktop/NetworkManager/Settings/0 yes wlan0 activated /org/freedesktop/NetworkManager/ActiveConnection/1
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH CONNECTION CON-UUID CON-PATH
 wlan0 wifi connected /org/freedesktop/NetworkManager/Devices/2 system76_5g 74de1f59-702b-4d15-9803-82b281989bed /org/freedesktop/NetworkManager/ActiveConnection/1
 eth0 ethernet unavailable /org/freedesktop/NetworkManager/Devices/1 -- -- --
 lo loopback unmanaged /org/freedesktop/NetworkManager/Devices/0 -- -- --
nmcli-nm: Error: command ['nmcli', '-f', 'all', 'nm'] failed with exit code 2: Error: Object 'nm' is unknown, try 'nmcli help'.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[BenTLor (social-d)]

For me the situation is slightly different but the result is the same:
Connect to WiFi
 - internet connection works
Connect LAN cable (note that wifi is still active and nm sets up eth0 correctly)
 - internet connection breaks, although route -n shows both interfaces and routes.

Expected: when I connect eth0, it is preferred over wifi (either with metric or disconnecting wifi entirely, I don't care) and thus routing works as normal.