[Qemu-devel] About network bridge.

[Qemu-devel] About network bridge.

[Yaodong Yang]

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Hello everyone,

Thanks for reading my email. I got a question about the network bridge in qemu-kvm.

When I start my vm using virsh start vm2 or virt-manager, the vm's network is working. I can access the internet within the vm. 
However, we I start the same vm using qemu-system-x86_64 vm2.img -m 1024. The vm can run but without internet access. I do not know the reason, can someone give me a direction?

The procedure to set up the system.
1. install the host os, set up bridge networking.
2. use virt-manager create guest vm, choose bridge network in the creation option of virt-manager.
3. run the guest vm.

My system configuration is as follows:

1. Host OS, Ubuntu 12.10 server with a kubuntu-desktop.
2. QEMU-KVM version is 1.2.0.
3. Host network configuration is bridge type, as follows:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto em1
iface em1 inet manual

auto br0
iface br0 inet static
        address 192.168.1.2
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255
        gateway 192.168.1.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 129.93.6.189

        bridge_ports em1
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

4. Guest OS ubuntu-server 12.10. network configuration is as follows:
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
        address 192.168.1.12
        netmask 255.255.255.0
        network 192.168.1.0
        broadcast 192.168.1.255
        gateway 192.168.1.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 129.93.6.189

Thanks!

Best,
Yaodong
----------------------------------------------
Yaodong Yang
Ph.D. Student
Department of Computer Science & Engineering
University of Nebraska-Lincoln 
Email: yaodong.yangy@gmail.com OR yyang@cse.unl.edu





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Re: [Qemu-devel] About network bridge.

[Stefan Hajnoczi]

On Mon, Apr 22, 2013 at 09:54:02AM -0500, Yaodong Yang wrote:
> When I start my vm using virsh start vm2 or virt-manager, the vm's network is working. I can access the internet within the vm. 
> However, we I start the same vm using qemu-system-x86_64 vm2.img -m 1024. The vm can run but without internet access. I do not know the reason, can someone give me a direction?

libvirt (virsh and virt-manager) configures networking for you.

When you run QEMU manually you need to do things yourself.  If you are
running x86 guests on x86 hosts, you should probably use virsh or
virt-manager instead of manually running QEMU.  It will save a lot of
time.

If you need to test custom QEMU binaries, you can simply edit the
<emulator> domain XML tag using virsh edit.

If you really want to manually run QEMU then please read the man page.
Also see http://qemu-project.org/Documentation/Networking and then do a
web search.  There are plenty of guides to setting up networking with
QEMU.

Stefan