Network operating system for managing and securing networks

Systems and methods for managing a network are described. A view of current state of the network is maintained where the current state of the network characterizes network topology and network constituents, including network entities and network elements residing in or on the network. Events are announced that correspond to changes in the state of the network and one or more network elements can be configured accordingly. Methods for managing network traffic are described that ensure forwarding and other actions taken by network elements implement globally declared network policy and refer to high-level names, independently of network topology and the location of network constituents. Methods for discovering network constituents are described, whereby are automatically configured. Routing may be performed using ACL and packets can be intercepted to permit host to continue in sleep mode. The methods are applicable to virtual environments.