Which of the following is a part of computer network that is used to prevent unauthorized Internet users from accessing private networks connected to the Internet?

A.
Protocol analyzer

B.
Wired Equivalent Privacy

C.
Intrusion detection system

D.
Firewall

Explanation:
A firewall is a part of a computer system or network that is designed to block unauthorized access while permitting authorized communications. It is a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all computer traffic between different security domains based upon a set of rules and other criteriA.The four important roles of a firewall are as follows:

1. Implement security policy: A firewall is a first step in implementing security policies of an organization. Different policies are directly implemented at the firewall. A firewall can also work with network routers to implement Types-Of-Service (ToS) policies.
2. Creating a choke point: A firewall can create a choke point between a private network of an
organization and a public network. With the help of a choke point the firewall devices can monitor, filter, and verify all inbound and outbound traffic.
3. Logging Internet activity: A firewall also enforces logging of the errors and faults. It also provides alarming mechanism to the network.
4. Limiting network host exposure: A firewall can create a perimeter around the network to protect it from the Internet. It increases the security by hiding internal information. Answer option C is incorrect. Intrusion detection (ID) is a type of security management system for computers and networks. An ID system gathers and analyzes information from various areas within a computer or a network to identify possible security breaches, which include both intrusions (attacks from outside the organization) and misuse (attacks from within the organization). ID uses vulnerability assessment (sometimes referred to as scanning), which is a technology developed to assess the security of a computer system or network. Intrusion detection functions include the following: Monitoring and analyzing both user and system activities Analyzing system configurations and vulnerabilities Assessing system and file integrity Ability to recognize patterns typical of attacks Analysis of abnormal activity patterns Tracking user policy violations Answer option B is incorrect. Wired Equivalent Privacy (WEP) is a security protocol for wireless local area networks (WLANs). It has two components, authentication and encryption. Itprovides security, which is equivalent to wired networks, for wireless networks. WEP encrypts data on a wireless network by using a fixed secret key. WEP incorporates a checksum in each frame to provide protection against the attacks that attempt to reveal the key stream.

Answer option A is incorrect. Protocol analyzer (also known as a network analyzer, packet analyzer or sniffer, or for particular types of networks, an Ethernet sniffer or wireless sniffer) is computer software or computer hardware that can intercept and log traffic passing over a digital network. As data streams flow across the network, the sniffer captures each packet and, if needed, decodes and analyzes its content according to the appropriate RFC or other specifications.