i am having a problem connecting VMs to the bridge interface. My VMs cannot connect to the host and LAN outside the host, when i ping it just say destination host unreachable. it seems that my VM is not connected to the br0 interface. I use redhat 5.6 on the host and centos 6 as VMs

i modify ifcfg-br0 interface with this:


my server connects to the outside network with bond0 interface, i modify ifcfg-bond0 like this:

BONDING_OPTS="mode=4 miimon=50"

i use bond0 as my KVM guest's network interface

here is ifcfg-eth0 configuration inside my CentOS KVM guest:


here is the output of brctl show:

bridge name         bridge id               STP enabled     interfaces
br0             8000.bc305be8c04f       no                  bond0

i've disable netfilter for bridge interface, restarting network service but no luck if anyone know where the problem is, please your help :'(

  • how do you start the VM? it should run the qemu-ifup script which creates the tap device and plugs it into the bridge. post the VM run command (ps -ef |grep qemu) and if you're using libvirt, the domxml contents (virsh dumpxml VMNAME) – dyasny Aug 26 '13 at 3:57
  • here is the output of "ps -ef |grep qemu" /usr/libexec/qemu-kvm -hda /usr/kvm_disk/Clinic.disk.xm -cdrom /opt/iso/CentOS-6.4-x86_64-LiveCD.iso -net nic,vlan=0,macaddr=,model=pcnet -net tap,vlan=0,script=/etc/kvm/qemu-ifup-br0 -usb -boot c -m 1024 -no-acpi -vnc :20 -name Clinic -usbdevice tablet -uuid ea852d3d-7adb-6db2-c652-a39672a23d60 -smp 2 -monitor unix:/var/run/kvm/monitors/Clinic,server,nowait -pidfile /var/run/kvm/pids/Clinic -daemonize. i actually use convirture to manage my KVM [link]convirture.com/products_opensource.php[/link] i have the qemu-ifup script – user1677104 Aug 26 '13 at 7:55
  • when the VM is started, brctl show doesn't show it attached, right? And what does ifconfig -a show, with a running VM? – dyasny Aug 26 '13 at 15:04

First, make sure your host network configuration is working correctly. In your Virtual machine configuration file, use "br0" as the networking interface.

<interface type='bridge'>
  <mac address='xx:xx:xx:xx:xx:xx'/>
  <source bridge='br0'/>
  <model type='virtio'/>
  • i actually use convirture to manage(create and start) my KVM VMs. I check the convirture configuration for my VM, and i have line specifying the VM to use br0 bridge interface kernel = '/usr/lib/xen/boot/hvmloader' vif = ['mac=$AUTOGEN_MAC, bridge=br0,model=pcnet'] auto_start_vm = 1 extra = '' stdvga = 0 i have asked this problem on convirture forums but still don't get any clue – user1677104 Aug 26 '13 at 8:05
  1. Stop using pcnet, switch to virtio.
  2. -net nic,vlan=1,macaddr=00:1a:4a:01:00:0a,model=virtio -net tap,vlan=1,ifname=vnet0,script=/etc/kvm/qemu-ifup-br0 this is what it should look like normally. You are missing a MAC address in the first section.
  • thanks dyasny, i will try it, the problem is we want to use convirture to manage(including starting) VMs and i haven't found it's documentation about how it's vm configuration file affect the qemu-kvm command to start vm. You are right it seems the mac address is not generated and it doesn't add interface, will figure it out and get back here to post the result – user1677104 Aug 28 '13 at 0:34
  • well, if it's so bad, I'd switch to a system written by the KVM people - oVirt – dyasny Aug 28 '13 at 3:09

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