|  |  | Perimeter security involves setting up a protective wall around your network. A network must have controlled entry and exit points to monitor network traffic in order to protect its vulnerabilities; without these checkpoints, hackers can slip into a network with little difficulty. When defining the perimeter, you must be able to distinguish the border between the inside and outside network. Network devices at the perimeter devices of the network are used to implement a portion of the security policy. The security policy which defines how the internal and external networks are connected.