What are two security appliances that can be installed in a network?

Intrusion detection system (IDS) and intrusion prevention system (IPS) solutions form an integral part of a robust network defense solution.

IDS monitors network and system activities for malicious activities or policy violations and produces reports to a Management Station.

IPS provides policies and rules for network traffic along with an intrusion detection system for alerting system or network administrators to suspicious traffic, but allows the administrator to provide the action upon being alerted.

The key to differentiating an IDS from an IPS is that an IPS responds immediately and does not allow any malicious traffic to pass, whereas an IDS allows malicious traffic to pass before it can respond.

(Reference: Implementing Cisco IOS Network Security IINS)

Note: Asynchronous Transfer Mode (ATM) is a layer 2 WAN transport protocol. It encodes data into small, fixed-sized cells consisting of 48 bytes of payload and 5 bytes of cell header -> A is not correct

Cisco Router and Security Device Manager (SDM) is a Web-based device-management tool for Cisco routers that can help you configure a router via a web browser -> In general, it only helps simplify the network management, router configuration so it is not a security appliance -> F is not correct.