When we consider security for networks (a critical part of network management), the situation is even more complicated. The additional security devices/middle-boxes (e.g., network intrusion detection system and firewall) significantly complicate
network configuration/management (e.g., which location to install which device to satisfy the different security needs from different networks while minimizing the overall cost). In addition, security devices have many diverse security functions to
serve different purposes. For example, we can use a firewall to control network access, a network intrusion detection system (NIDS) to monitor exploit attacks in network payloads, and a network anomaly detection system to detect DDoS attacks. Therefore, the network administrator should choose reasonable security functions/devices and deploy them into reasonable places. However, it is a tough task for the administrator,
because it is hard to predict possible network threats of different network tenants and the administrator is not able to be aware of demands of diverse tenants in advance. Thus, those installed security functions/appliances/devices may not
be in the best locations that can best serve the diverse security needs of diverse network users.