Several countries have deployed, or have started the deployment of a smart metering infrastructure in order to enable the Smart Grid. This infrastructure aims to provide new services to grid users and grid operators relying on several communication technologies. One of the goals of this infrastructure is to improve energy consumption, for instance by increasing the awareness of the users, or by enforcing energy management policies. Yet, this infrastructure also consumes energy. The objective of this work is to accurately characterize the energy consumption of each part of the smart metering infrastructure, at a nation-wide scale. We also explore several consumption scenarios highlighting the impact of legacy technologies on the energy consumption of the smart metering infrastructure.