Mark works as a project engineer in Tech Perfect Inc.

A proxy server exists between a client's Web-browsing program and a real Internet server. The purpose of the proxy server is to enhance the performance of user requests and filter requests. A proxy server has a database called cache where the most frequently accessed Web pages are stored. The next time such pages are requested, the proxy server is able to suffice the request locally, thereby greatly reducing the access time. Only when a proxy server is unable to fulfill a request locally does it forward the request to a real Internet server. The proxy server can also be used for filtering user requests. This may be done in order to prevent the users from visiting non-genuine sites. Answer: D is incorrect. Transmission Control Protocol/Internet Protocol (TCP/IP) is a suite of standard protocols that govern how data passes between networks. It can be used to provide communication between the basic operating systems on local and wide-area networks (WANs). TCP/IP is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an intranet or an extranet). It is considered the primary protocol of the Internet and the World Wide Web. Answer: B is incorrect. IP packet filters allow or block packets from passing through specified ports. They can filter packets based on service type, port number, source computer name, or destination computer name. When packet filtering is enabled, all packets on the external interface are dropped unless they are explicitly allowed, either statically by IP packet filters or dynamically by access policy or publishing rules. Answer: C is incorrect. A router is a device that routes data packets between computers in different networks. It is used to connect multiple networks, and it determines the path to be taken by each data packet to its destination computer. A router maintains a routing table of the available routes and their conditions. By using this information, along with distance and cost algorithms, the router determines the best path to be taken by the data packets to the destination computer. A router can connect dissimilar networks, such as Ethernet, FDDI, and Token Ring, and route data packets among them. Routers operate at the network layer (layer 3) of the Open Systems Interconnection (OSI) model.