An application proxy provides the most comprehensive filtering of Peer-to-Peer (P2P) traffic. P2P traffic is a type of network traffic that involves direct communication and file sharing between peers, without the need for a central server. P2P traffic can be used for legitimate purposes, such as distributed computing, content delivery, or collaboration, but it can also be used for illegal or malicious purposes, such as piracy, malware distribution, or denial-of-service attacks. P2P traffic can also consume a lot of bandwidth and degrade the performance of other network applications. Therefore, it may be desirable to filter or block P2P traffic on a network. An application proxy is a type of firewall that operates at the application layer of the OSI model, and acts as an intermediary between the client and the server. An application proxy can inspect the content and the behavior of the network traffic, and apply granular filtering rules based on the specific application protocol, such as HTTP, FTP, or SMTP. An application proxy can also perform authentication, encryption, caching, and logging functions. An application proxy can provide the most comprehensive filtering of P2P traffic, as it can identify and block the P2P applications and protocols, regardless of the port number or the payload. An application proxy can also prevent P2P traffic from bypassing the firewall by using encryption or tunneling techniques. The other options are not as effective as an application proxy for filtering P2P traffic. A port filter is a type of firewall that operates at the transport layer of the OSI model, and blocks or allows traffic based on the source and destination port numbers. A port filter cannot inspect the content or the behavior of the traffic, and cannot distinguish between different applications that use the same port number. A port filter can also be easily evaded by P2P traffic that uses random or well-known port numbers, such as port 80 for HTTP. A network boundary router is a router that connects a network to another network, such as the Internet. A network boundary router can perform some basic filtering functions, such as access control lists (ACLs) or packet filtering, but it cannot inspect the content or the behavior of the traffic, and cannot apply granular filtering rules based on the specific application protocol. A network boundary router can also be easily evaded by P2P traffic that uses encryption or tunneling techniques. An access layer switch is a switch that connects end devices, such as PCs, printers, or servers, to the network. An access layer switch can perform some basic filtering functions, such as MAC address filtering or port security, but it cannot inspect the content or the behavior of the traffic, and cannot apply granular filtering rules based on the specific application protocol. An access layer switch can also be easily evaded by P2P traffic that uses encryption or tunneling techniques. References: Why and how to control peer-to-peer traffic | Network World; Detection and Management of P2P Traffic in Networks using Artificial Neural Networksa | Journal of Network and Systems Management; Blocking P2P And File Sharing - Cisco Meraki Documentation.
