I'm trying to make network bridging to work on a Ubuntu 15.04 (I'm experimenting in order to make a QEMU/KVM virtual machine that will be visible to the outside network as if it were a distinct machine). The problem is that when I type brctl addif br0 eth0 then I lose connectivity to the network.

  • Define the bridge interface with eth0 as port
  • Set the IP address on the bridge interface

You will need the bridge-utils package installed (most likely is already there). Here's how you would configure this in /etc/network/interfaces. Restart the network service (or reboot the machine)

auto lo
iface lo inet loopback

auto  eth0
iface eth0 inet manual

auto bridge0
iface bridge0 inet static
  address   <your public ip>
  netmask   <netmask value>
  gateway   <your gateway>
  bridge_ports eth0
  bridge_stp off       # disable Spanning Tree Protocol
  bridge_waitport 0    # no delay unless port available
  bridge_fd 0          # no forwarding delay
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You need to remove IP address configuration from eth0, add eth0 to the bridge and then configure IP address on the br0 interface.

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