The idea is to meter this as the L3 routers levels. The point is to allow operators to configure IP ranges and to assign a label to them. For example we will be able to set two labels; one for the internal traffic, and the other one for the external traffic. Each label will measure the traffic for a specific set of ip range. Then, bandwidth measurement will be send for each label to the Oslo notification system and could be collected by Ceilometer.
https://blueprints.launchpad.net/neutron/+spec/bandwidth-router-label https://blueprints.launchpad.net/neutron/+spec/bandwidth-router-measurement https://blueprints.launchpad.net/ceilometer/+spec/ceilometer-quantum-bw-metering