Comment 0 for bug 997978

System:
-----------
Dell R410 Dual processor 2.4Ghz w/16G RAM
Distributor ID: Ubuntu
Description: Ubuntu 12.04 LTS
Release: 12.04
Codename: precise

Setup:
---------
We're running 3 KVM guests, all Ubuntu 12.04 LTS using bridged networking.

From the host:
# cat /etc/network/interfaces
auto br0
iface br0 inet static
        address 212.XX.239.98
        netmask 255.255.255.240
        gateway 212.XX.239.97
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

# ifconfig eth0
eth0 Link encap:Ethernet HWaddr d4:ae:52:84:2d:5a
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:11278363 errors:0 dropped:3128 overruns:0 frame:0
          TX packets:14437384 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:4115980743 (4.1 GB) TX bytes:5451961979 (5.4 GB)
          Interrupt:36 Memory:da000000-da012800

# ifconfig br0
br0 Link encap:Ethernet HWaddr d4:ae:52:84:2d:5a
          inet addr:212.XX.239.98 Bcast:212.XX.239.111 Mask:255.255.255.240
          inet6 addr: fe80::d6ae:52ff:fe84:2d5a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:1720861 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1708622 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:210152198 (210.1 MB) TX bytes:300858508 (300.8 MB)

# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.d4ae52842d5a no eth0

I have no default network configured to autostart in libvirt as we're using bridged networking:
# virsh net-list --all
Name State Autostart
-----------------------------------------
default inactive no

# arp
Address HWtype HWaddress Flags Mask Iface
mailer03.xxxx.com ether 52:54:00:82:5f:0f C br0
mailer01.xxxx.com ether 52:54:00:d2:f7:31 C br0
mailer02.xxxx.com ether 52:54:00:d3:8f:91 C br0
dxi-gw2.xxxx.com ether 00:1a:30:2a:b1:c0 C br0

From one of the guests:
<domain type='kvm' id='4'>
  <name>mailer01</name>
  <uuid>d41d1355-84e8-ae23-e84e-227bc0231b97</uuid>
  <memory>2097152</memory>
  <currentMemory>2097152</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/dev/mapper/vg_main-mailer01--root'/>
      <target dev='hda' bus='ide'/>
      <alias name='ide0-0-0'/>
      <address type='drive' controller='0' bus='0' unit='0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/dev/mapper/vg_main-mailer01--swap'/>
      <target dev='hdb' bus='ide'/>
      <alias name='ide0-0-1'/>
      <address type='drive' controller='0' bus='0' unit='1'/>
    </disk>
    <controller type='ide' index='0'>
      <alias name='ide0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:d2:f7:31'/>
      <source bridge='br0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/0'/>
      <target port='0'/>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/0'>
      <source path='/dev/pts/0'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='5900' autoport='yes' listen='127.0.0.1'>
      <listen type='address' address='127.0.0.1'/>
    </graphics>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </memballoon>
  </devices>
  <seclabel type='dynamic' model='apparmor' relabel='yes'>
    <label>libvirt-d41d1355-84e8-ae23-e84e-227bc0231b97</label>
    <imagelabel>libvirt-d41d1355-84e8-ae23-e84e-227bc0231b97</imagelabel>
  </seclabel>
</domain>

From within the guest:
# cat /etc/network/interfaces
# The primary network interface
auto eth0
iface eth0 inet static
        address 212.XX.239.100
        netmask 255.255.255.240
        network 212.XX.239.96
        broadcast 212.XX.239.111
        gateway 212.XX.239.97

# ifconfig
eth0 Link encap:Ethernet HWaddr 52:54:00:d2:f7:31
          inet addr:212.XX.239.100 Bcast:212.XX.239.111 Mask:255.255.255.240
          inet6 addr: fe80::5054:ff:fed2:f731/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:5631830 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6683416 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:2027322829 (2.0 GB) TX bytes:2076698690 (2.0 GB)

A commandline which starts the KVM guest:
/usr/bin/kvm -S -M pc-1.0 -enable-kvm -m 2048 -smp 1,sockets=1,cores=1,threads=1 -name mailer01 -uuid d41d1355-84e8-ae23-e84e-227bc0231b97 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/mailer01.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -drive file=/dev/mapper/vg_main-mailer01--root,if=none,id=drive-ide0-0-0,format=raw -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 -drive file=/dev/mapper/vg_main-mailer01--swap,if=none,id=drive-ide0-0-1,format=raw -device ide-drive,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1 -netdev tap,fd=18,id=hostnet0 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:d2:f7:31,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -vnc 127.0.0.1:0 -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4

Problem:
------------
Periodically (at least once a day), one or more of the guests lose network connectivity. Ping responds with 'host unreachable', even from the dom host. Logging in via the serial console shows no problems: eth0 is up, can ping the local host, but no outside connectivity. Restart the network (/etc/init.d/networking restart) does nothing. Reboot the machine and it comes alive again.

I've verified there's no arp games going on on the primary host (the arp tables remain the same before - when it had connectivity - and after - when it doesn't.

This is a critical issue affecting production services on the latest LTS release of Ubuntu. It's similar to an issue which was 'resolved' in 10.04 but appears to have risen its ugly head again.