Neutron uses a default empty string for Neutron's external bridge mapping. This maps the physical interface to the
br-int instead of the using
br-ex directly. This model allows multiple floating IP networks using either VLANs or multiple physical connections
NeutronExternalNetworkBridge parameter in the
parameter_defaults section of your network isolation environment file:
# Set to "br-ex" when using floating IPs on the native VLAN
Using only one Floating IP network on the native VLAN of a bridge means you can optionally set the Neutron external bridge. This results in the packets only having to traverse one bridge instead of two, which might result in slightly lower CPU usage when passing traffic over the Floating IP network.
The next section contains changes to the NIC config to put the External network on the native VLAN. If the External network is mapped to
br-ex, you can use the External network for Floating IPs in addition to the Horizon dashboard and Public APIs.