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I am currently renting an Ubuntu server. On this machine I would like to run virtual machines using KVM. For some web access I have installed Kimchi, a very simple html5-based KVM management tool.

Anyway I have problems setting up the networking for the virtual machines. At the moment I have one main IP and multiple additional IPs. The main IP is reserved for the host so I can access it per SSH etc. Please note that the host server is directly connected to the internet with this public IP, there is nothing in between.

Obviously now I would like to make the first virtual machine use one of the additional IPs.

This is /etc/network/interfaces so far:

auto lo
iface lo inet loopback

# device: eth0
auto  eth0
iface eth0 inet static
  address   1**.***.***.**6
  broadcast 1**.***.***.**1
  netmask   2**.***.***.**2
  gateway   1**.***.***.**9
  # default route to access subnet
  up route add -net 1**.***.***.**8 netmask 2**.***.***.**2 gw 1**.***.***.**9 eth0

enter image description here

The Kimchi web administration gives me the following options. I can create a new network which can be attached to a virtual machine:

enter image description here

How would I need to set up in order to let a virtual machine use an additional IP automatically?

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Here is a more detailed walkthrough of bridging:

Follow these steps on the kvm server:

sudo stop network-manager

echo "manual" | sudo tee /etc/init/network-manager.override

That will disable your network-manager and prevent it from restarting.

next we work on the interface config, starting by taking the interface down:

ifdown eth0

edit "/etc/network/interfaces" and find the physical interface, likely eth0

You need to replace the eth0 interface information, to make it look like the following:

auto br0
   iface br0 inet static
       address XXX.XXX.X.X
       netmask XXX.XXX.XXX.x
       network XXX.XXX.X.X
       broadcast XXX.XXX.XXX.X
       gateway XXX.XXX.X.X
       bridge_ports eth0
       bridge_stp on
       bridge_maxwait 0

You shoudl be able to then bring back your adapter with:

ifup br0

you also need to add the following to your '/etc/sysctl.conf' settings

net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

and load settings with

sysctl -p /etc/sysctl.conf

Also add the line's

/sbin/sysctl -p /etc/sysctl.conf
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

to your '/etc/rc.local' file, just before the "exit 0" line to ensure these effects start at boot.

run brctl show

and look for a br0 line that shows the interface eth0. This is now a bridgeable device.

You now need to configure your guest VM's to point to this bridge. on your guests definition XML files

virsch edit <name of guest VM>

You need to edit the interface section to look similar to:

<interface type='bridge'>
        <source bridge='br0'/>
        <mac address='<YOUR MAC ADDRESS>'/>
        <model type='virtio'/>   # try this if you experience problems with VLANs
     </interface>

Your devices should now be bridged. You will still need to configure IP addresses on the machines themselves correctly

Also after having gone through all the other pages for information for this. I also found this nice little tutorial that may be of help in understanding everything:

http://www.dedoimedo.com/computers/kvm-bridged.html

  • I have only one physical network device (LAN) but multiple IPs. It would help me a lot if you could get into a bit more details in the interfaces file, I did not really understand how to place my two IPs in there. Thanks a lot! – andreas Feb 8 '15 at 17:18
  • @andreas Added some more clarified information. The following link may also prove usefull: wiki.libvirt.org/page/Networking – Gravy Feb 8 '15 at 20:10

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