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my vm is centos 4.8 and it came from a physical server. All is great except I can't seem to get bridged networking working. The default user mode networking is fine, from the guest I can reach the internet but I want to bridge so the host can see the guest.

I've read some docs about it but it feels like I'm missing the big picture and am getting confused. Am I setting up the bridge network interface on the host? And what role does the config files in /etc/libvirt play? I see that when I use the virtual machine manager, it adds xml files there but what about the network interface stuff. Is that modifying the host system when the libvirt service starts?

Bob Frank
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The bridge network interface is setup on the host computer. When you use bridging the guest network interface uses the host bride interface. The .xml files in /etc/libvirt/qemu define the VM, and therefore play an all important role. If you are using bridging, there should be lines similar to:

<interface type='bridge'>
  <mac address='52:54:00:87:d2:f4'/>
  <source bridge='br0'/>
  <model type='virtio'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>

I do not use virt manager, but this and this might help you.

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Doug Smythies
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  • Thanks for the reply. This is a confusing topic because you have addons like bridge helper and bridge utils, plus libvirt doing things for you as well as docs which step you through using -net and more recent ones saying -net is obsoleted. I'm looking for the command line syntax, here's what I have: – Bob Frank Dec 06 '15 at 17:04
  • here's what I have: kvm -m 4096 -hda sda.img -device e100,netdev=net0 -netdev tap,id=net0. I don't know what I'm doing there. I have a bridge interface br0 setup on host and working, tied to eth0. – Bob Frank Dec 06 '15 at 17:11
  • Oh and I did get this working in libvirt but I want to do this from shell and then turn it into a script for turning my machine on and off. I'm trying not to use libvirt – Bob Frank Dec 06 '15 at 17:13
  • Did you consider to do a virt-install of your disk image and thereafter just use `virsh start vname` to start it? You could use `virsh shutdown vname` to turn it off, but it would make more sense to shutdown the VM from within the VM itself. Have a look at the basic command [here](http://blog.allanglesit.com/2011/03/kvm-guests-using-virt-install-to-import-an-existing-disk-image/) – Doug Smythies Dec 06 '15 at 18:11
  • I got it solved. Thanks for the hints. So final script that works for me is kvm -m 4096 -hda sda.img -device e1000,netdev=net0 -netdev=tap,id=net0. Prior to this I set up bridging on host as described here: https://help.ubuntu.com/community/BridgingNetworkInterfaces – Bob Frank Dec 06 '15 at 18:28