Bridged Networking

This guide describes how to deploy Bridged networks. In this mode, the virtual machine traffic is directly bridged through the Linux bridge in the nodes. Bridged networks can operate in four different modes depending on the additional traffic filtering made by the OpenNebula:

  • Dummy Bridged, no filtering, no bridge setup (legacy no-op driver).
  • Bridged, no filtering is made, managed bridge.
  • Bridged with Security Groups, iptables rules are installed to implement security groups rules.
  • Bridged with ebtables VLAN, same as above plus additional ebtables rules to isolate (L2) each Virtual Networks.

Considerations & Limitations

The following needs to be considered regarding traffic isolation:

  • In the Dummy Bridged, Bridged and Bridged with Security Groups modes you can add tagged network interfaces to achieve network isolation. This is the recommended deployment strategy in production environments in this mode.
  • The Bridged with ebtables VLAN mode is targeted to small environments without proper hardware support to implement VLANS. Note that it is limited to /24 networks and that IP addresses cannot overlap between Virtual Networks. This mode is only recommended for testing purposes.

OpenNebula Configuration

The following configuration attributes can be adjusted in /var/lib/one/remotes/etc/vnm/OpenNebulaNetwork.conf:

Parameter Description
ipset_maxelem Maximal number of entries in the IP set (used for the security group rules)
keep_empty_bridge Set to true to preserve bridges with no virtual interfaces left.
bridge_conf Hash Options for brctl

Defining a Bridged Network

To create a virtual network include the following information:

Attribute Value Mandatory
VN_MAD
  • dummy for the Dummy Bridged mode
  • bridge for the Bridged mode
  • fw for Bridged with Security Groups
  • ebtables for Bridged with ebtables isolation
YES
BRIDGE Name of the linux bridge in the nodes YES
PHYDEV Name of the physical network device that will be attached to the bridge (does not apply for dummy driver) NO

The following example defines Bridged network with the Security Groups mode:

NAME    = "bridged_net"
VN_MAD  = "fw"
BRIDGE  = vbr1
...

ebtables VLAN Mode: default rules

This section lists the ebtables rules that are created, in case you need to debug your setup

# Drop packets that don't match the network's MAC Address
-s ! <mac_address>/ff:ff:ff:ff:ff:0 -o <tap_device> -j DROP
# Prevent MAC spoofing
-s ! <mac_address> -i <tap_device> -j DROP