The energy consumption of the Information and Communication Technology (ICT) sector has been increasing recently; this sector is estimated to account for 2% of the total energy consumption. An even more aggressively increasing trend is the volume of Internet traffic and the number of connected devices. Thus, reducing the energy needs of the Internet is recognized as one of the main challenges that the ICT sector will have to face in the near future to reduce its overall energy footprint. Introducing energy-efficient techniques, both at the device level and the network level is required. The main goal of this work is to quantitatively evaluate the potential energy savings from applying energy-efficient techniques while examining the trade-off between network performance and the achieved energy savings. We introduce a categorisation of the energy-aware design space, focusing on the existing techniques in the device data plane, and contribute an analytical framework to represent the impact of energy-aware technologies and solutions for network devices. Our energy profile model represents the diverse energy-aware states of the network devices and is applied to two reference scenarios, one of a large-scale Telco (Telecom Italia) and one of a medium size Internet Service Provider (GRNET), to evaluate the impact of each energy-aware technology and the energy savings potential at the Home, Access, Metro/Transport and Core parts of each network. The results show the estimates of energy savings exceed 60% in many cases while maintaining the same quality of service as in the energy-agnostic case.