Connecting LXC or any other type of virtual machine such as KVM or Xen, the hypervisor layer, or in the case of LXC, the host OS, requires the ability to bridge traffic between the containers/VMs and the outside world. Software bridging in Linux has been supported since the kernel version 2.4. To take advantage of this functionality, bridging needs to be enabled in the kernel by setting Networking support | Networking options | 802.1d Ethernet Bridging to yes, or as a kernel module when configuring the kernel.

To check what bridging options are compiled in the kernel, or available as modules, run the following command:

root@host:~# cat /boot/config-`uname -r` | grep -ibridge
# PC-card bridges
CONFIG_BRIDGE_NETFILTER=y
CONFIG_NF_TABLES_BRIDGE=m
CONFIG_BRIDGE_NF_EBTABLES=m
CONFIG_BRIDGE_EBT_BROUTE=m
CONFIG_BRIDGE_EBT_T_FILTER=m
CONFIG_BRIDGE_EBT_T_NAT=m
CONFIG_BRIDGE_EBT_802_3=m
CONFIG_BRIDGE_EBT_AMONG=m
CONFIG_BRIDGE_EBT_ARP=m
CONFIG_BRIDGE_EBT_IP=m
CONFIG_BRIDGE_EBT_IP6...