Public bug reported: This is similar to #961089 and may well be a duplicate, but I believe that there's a distinction since NM is disabling a bridge that's been created automatically by virt-manager, and so the explanation that it's not a normal way of configuring bridges doesn't (or at least shouldn't) apply.
Basically, what I've done is: 1) Install virt-manager 2) Create some VMs 3) Leave my machine on for a while 4) Notice that the bridge disappears and none of the machines can speak to the host (or get DHCP leases). I noticed this earlier today, and so added the mac address of the bridge to Network Manager's config, but it appears to have ignored this, too: root@amazing:/home/avi# tail -n1 /etc/NetworkManager/NetworkManager.conf unmanaged-devices=mac:fe:54:00:43:19:37 root@amazing:/home/avi# ifconfig virbr0 virbr0 Link encap:Ethernet HWaddr fe:54:00:43:19:37 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1723 errors:0 dropped:0 overruns:0 frame:0 TX packets:2140 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:200990 (200.9 KB) TX bytes:1822872 (1.8 MB) root@amazing:/home/avi# I see this in syslog at about the same time (grepping for virbr0): Jan 15 17:50:13 amazing NetworkManager[1261]: <info> (virbr0): now managed Jan 15 17:50:13 amazing NetworkManager[1261]: <info> (virbr0): device state change: unmanaged -> unavailable (reason 'managed') [10 20 2] Jan 15 17:50:13 amazing NetworkManager[1261]: <info> (virbr0): bringing up device. Jan 15 17:50:13 amazing avahi-daemon[652]: Joining mDNS multicast group on interface virbr0.IPv4 with address 192.168.122.1. Jan 15 17:50:13 amazing avahi-daemon[652]: New relevant interface virbr0.IPv4 for mDNS. Jan 15 17:50:13 amazing avahi-daemon[652]: Registering new address record for 192.168.122.1 on virbr0.IPv4. Jan 15 17:50:13 amazing NetworkManager[1261]: <info> (virbr0): carrier now ON (device state 20) Jan 15 17:50:13 amazing NetworkManager[1261]: <info> (virbr0): deactivating device (reason 'managed') [2] Jan 15 17:50:13 amazing avahi-daemon[652]: Withdrawing address record for 192.168.122.1 on virbr0. Jan 15 17:50:13 amazing avahi-daemon[652]: Leaving mDNS multicast group on interface virbr0.IPv4 with address 192.168.122.1. Jan 15 17:50:13 amazing avahi-daemon[652]: Interface virbr0.IPv4 no longer relevant for mDNS. Jan 15 17:50:13 amazing NetworkManager[1261]: <info> (virbr0): device state change: unavailable -> disconnected (reason 'none') [20 30 0] Jan 15 17:50:17 amazing dnsmasq-dhcp[1932]: DHCP packet received on virbr0 which has no address Jan 15 17:50:19 amazing dnsmasq-dhcp[1932]: DHCP packet received on virbr0 which has no address Jan 15 17:50:26 amazing dnsmasq-dhcp[1932]: DHCP packet received on virbr0 which has no address Jan 15 17:50:27 amazing dnsmasq-dhcp[1932]: DHCP packet received on virbr0 which has no address ProblemType: Bug DistroRelease: Ubuntu 13.04 Package: network-manager 0.9.6.0+git201301021750.e78c3e8-0ubuntu1 ProcVersionSignature: Ubuntu 3.7.0-7.15-generic 3.7.0 Uname: Linux 3.7.0-7-generic x86_64 ApportVersion: 2.7-0ubuntu2 Architecture: amd64 Date: Tue Jan 15 17:57:47 2013 EcryptfsInUse: Yes IfupdownConfig: auto lo iface lo inet loopback InstallationDate: Installed on 2012-09-10 (127 days ago) InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha amd64 (20120910) IpRoute: default via 192.168.1.254 dev wlan0 proto static 169.254.0.0/16 dev wlan0 scope link metric 1000 192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.67 metric 9 MarkForUpload: True NetworkManager.state: [main] NetworkingEnabled=true WirelessEnabled=true WWANEnabled=true WimaxEnabled=true SourcePackage: network-manager UpgradeStatus: Upgraded to raring on 2012-11-26 (50 days ago) mtime.conffile..etc.NetworkManager.NetworkManager.conf: 2013-01-15T16:36:47.133697 nmcli-dev: DEVICE TYPE STATE DBUS-PATH virbr0 bridge disconnected /org/freedesktop/NetworkManager/Devices/2 wlan0 802-11-wireless connected /org/freedesktop/NetworkManager/Devices/1 eth0 802-3-ethernet unavailable /org/freedesktop/NetworkManager/Devices/0 nmcli-nm: RUNNING VERSION STATE NET-ENABLED WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN running 0.9.7.0 connected enabled enabled enabled enabled enabled ** Affects: network-manager (Ubuntu) Importance: Undecided Status: New ** Tags: amd64 apport-bug raring running-unity -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1099949 Title: Disables virtual machine manager's virbr0 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1099949/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs