The primary function of a proxy server is to act as an intermediary for requests between a client and a server. When a client requests a resource (e.g., a web page), the request is sent to the proxy server first. The proxy then forwards this request to the destination server on behalf of the client. This intermediation allows the proxy to enforce security policies, filter malicious content, cache data to improve performance, and mask the client's original IP address, thereby enhancing both security and privacy.

A. This describes the function of a basic router or switch. A proxy, by definition, intercepts, analyzes, and often modifies traffic, rather than just routing it directly.

B. Proxies are a security tool but do not replace firewalls. They work at different layers of the network model and are often used together to create a layered defense strategy.

C. While some specialized proxies (SSL/TLS proxies) decrypt and re-encrypt traffic for inspection, their primary function is not to encrypt all network traffic. This is more characteristic of a VPN.

1. Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. In Section 2.6.1, "Web Caching," a proxy server is defined as "a network entity that satisfies HTTP requests on the behalf of an origin Web server," establishing its role as an intermediary.

2. Zwicky, E. D., Cooper, S., & Chapman, D. B. (2000). Building Internet Firewalls (2nd ed.). O'Reilly & Associates. In Chapter 8, "Proxy Systems," the authors state, "A proxy server is a program that deals with the outside world on behalf of a protected host... Proxies are intermediaries."

3. Stanford University. (2021). CS 155: Computer and Network Security, Lecture 11: Network Security. Course materials. The lecture notes describe an application-level proxy as a system that "acts as an intermediary for requests from clients seeking resources from other servers," highlighting its fundamental role in brokering connections.