Re: [Qemu-discuss] Guest fails to reconnect after host network goes down

[Vlad Yasevich]

On 08/23/2015 07:31 AM, Davide Baldini wrote:
> Thanks Vlad,
> 
.. snip..
> 
> As far as I notice, there are no differences shown by `ifconfig`.
> The fact is, that all guests drop the network after a cable is unplugged and 
> then
> replugged, while the host's network keeps functioning.

What do you mean by "drop network"?   Is the link going down in the guest?  Is
the guest losing IP address?  Is the guest simply stops being reachable?

Are there any firewall rules on the host?

Thanks
-vlad

> 
> Where else can I look?
> 
> -- Davide
> 
> On 08/19/2015 08:02 PM, Vlad Yasevich wrote:
>> On 08/16/2015 12:55 PM, Davide Baldini wrote:
>>> When I unplug the ethernet cable from the physical host, guest fails to 
>>> reconnect; host
>>> does reconnect.
>>
>> What do you mean by 'reconnect'?  Unplugging the cable for the nic on the 
>> physical host
>> does not really disconnect the guest from the network.  According to the 
>> configuration
>> your provided, the guest is still connected to the bridge on the host and 
>> can still
>> communicate with other guests on the same host.
>>
>> Once the host network is plugged back in, the bridge should start forwarding 
>> packets
>> back to the guest.
>>
>>>
>>> A very simple configuration here, with an almost default Debian 7 on both 
>>> host and guest:
>>>
>>> -- ON HOST:
>>>
>>> /etc/network/interfaces
>>>
>>>    auto lo
>>>    iface lo inet loopback
>>>
>>>    auto br0
>>>    iface br0 inet dhcp
>>>        bridge_ports    eth1
>>>        bridge_stp      off
>>>        bridge_maxwait  0
>>>        bridge_fd       0
>>>
>>>
>>> -- ON GUEST:
>>>
>>> /etc/network/interfaces
>>>
>>>    auto eth0
>>>    allow-hotplug eth0
>>>    iface eth0 inet static
>>>        address 192.168.1.109
>>>        netmask 255.255.255.0
>>>        network 192.168.1.0
>>>        broadcast 192.168.1.255
>>>        gateway 192.168.1.1
>>>        dns-nameservers 192.168.1.1
>>>
>>>
>>> QEMU is started as:
>>>
>>> /usr/local/bin/qemu-system-x86_64 -hda /media/raid1/qemu-109 -m 8G -smp 4 
>>> -enable-kvm
>>> -netdev bridge,id=br109 -device 
>>> virtio-net-pci,netdev=br109,id=nic0,mac=00:00:00:00:01:09
>>> -k it -daemonize
>>>
>>> QEMU emulator version 2.3.0
>>>
>>> Nothing appears on dmesg. Any hints?
>>
>> Make sure that the bridge on the host is formed correctly after the cable 
>> has been plugged
>> back in.
>>
>> -vlad
>>
>>>
>>> -- Davide
>>>
>>
>