Proxy server- In computer networks, a proxy server is a server (a computer system or an application) that acts as an intermediary for requests from clients seeking resources from other servers.[1] A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server and the proxy server evaluates the request as a way to simplify and control its complexity.
Firewall - In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.[1] A firewall typically establishes a barrier between a trusted internal network and untrusted outside network, such as the Internet.[2]
A proxy server (running either on dedicated hardware or as software on a general-purpose machine) may act as a firewall by responding to input packets (connection requests, for example) in the manner of an application, while blocking other packets. A proxy server is a gateway from one network to another for a specific network application, in the sense that it functions as a proxy on behalf of the network user.[2]
Proxies make tampering with an internal system from the external network more difficult, so that misuse of one internal system would not necessarily cause a security breach exploitable from outside the firewall (as long as the application proxy remains intact and properly configured). Conversely, intruders may hijack a publicly reachable system and use it as a proxy for their own purposes; the proxy then masquerades as that system to other internal machines. While use of internal address spaces enhances security, crackers may still employ methods such as IP spoofing to attempt to pass packets to a target network.
So I -> A .. Now next
Kazaa, DC++ - Kazaa Media Desktop (once stylized as "KaZaA", but later usually written "Kazaa") started as a peer-to-peer file sharing application using the FastTrack protocol .DC++ is a free and open-source, peer-to-peer file-sharing client that can be used for connecting to the Direct Connect network or to the ADC protocol
P2P(Peer to Peer) - Forms a loose group and can communicate with others in the group . No need to distinguish client and servers in this architecture.
so II -> C .. Now next
Slip - SLIP means Serial Line Internet Protocol. SLIP is the result of the integration of modem protocols prior to the suite of TCP/IP protocols.It is a simple Internet link protocol conducting neither address or error control, this is the reason that it is quickly becoming obsolete in comparison to PPP.
PPP(point to point) - Data link layer (layer 2) protocol used to establish direct connection between two nodes (no host or router in between) . Example - Telephone .It is a much more developed protocol than SLIP (which is why it is replacing it).
So III -> D .. Now next
DNS - A DNS cache (sometimes called a DNS resolver cache) is a temporary database, maintained by a computer's operating system, that contains records of all the recent visits and attempted visits to websites and other internet domains.In other words, a DNS cache is just a memory of recent DNS lookups that your computer can quickly refer to when it's trying to figure out how to load a website
Caching - Caching is an area of a computer’s memory devoted to temporarily storing recently used information. The content, which includes HTML pages, images, files and Web objects, is stored on the local hard drive in order to make it faster for the user to access it, which helps improve the efficiency of the computer and its overall performance.
So IV -> B ... Option C ..