CLOUD computing exploits powerful resource management techniques to allow users to share a large pool of computational, network and storage resources over the Internet. The concept is inherited from research oriented grid computing and further expanded toward a business model where consumers are charged for the diverse offered services Distributed Energy Efficient Clouds Over Core Networks. Cloud computing is expected to be the main factor that will dominate the future Internet service model by offering a network based rather than desktop based users applications . Virtualization lies at the heart of cloud computing, where the requested resources are created, managed and removed flexibly over the existing physical machines such as servers, storage and networks. This opens the doors towards resource consolidation that cut the cost for the cloud provider and eventually, cloud consumers. However, cloud computing elastic management and Distributed Energy Efficient Clouds Over Core Networks economic advantages come at the cost of increased concerns regarding their privacy , availability and power consumption. Cloud computing has benefited from the work done on datacenters energy efficiency . However, the success of the cloud relies heavily on the network that connects the clouds to their users. This means that the expected popularity of the cloud services has implications on network traffic, hence, network power consumption, especially if we consider the total path that information traverses from clouds storage through its servers, internal LAN, core, aggregation and access network up to the users’ devices. For instance, the authors in have shown that Distributed Energy Efficient Clouds Over Core Networks transporting data in public and sometimes private clouds might be less energy efficient compared to serving the computational demands by traditional desktop. Designing future energy efficient clouds, therefore, requires the co-optimization of both external network and internal clouds resources. The lack of understanding of this interplay between the two domains of resources might cause eventual loss of power Distributed Energy Efficient Clouds Over Core Networks. For instance, a cloud provider might decide to migrate virtual machines (VMs) or content from one cloud location to another due to low cost or green renewable energy availability, however, the power consumption of the network through which users data traverse to/from the new cloud location might outweigh the gain of migration.