1. Key Terms:
    1. Proxy Server:
      1. A server that acts as an intermediary for requests from clients seeking resources from other servers.
    2. IP Proxy:
      1. A type of proxy server that secures a network by keeping machines behind it anonymous, using Network Address Translation.
    3. HTTP Proxy (Web Proxy):
      1. A type of caching web proxy that caches web pages from servers on the Internet for a set amount of time, in order to better serve the HTTP clients, and to reduce the traffic load placed on the original server.
    4. Proxy Auto-Configuration (PAC):
      1. A file used by a web browser to define the configuration settings for how the browser may automatically choose a proxy server.
      2. The PAC file and the embedded JavaScript function it depends on pose a security risk - the file can be exploited and modified, redirecting the user to unwanted (potentially malicious) websites.
      3. Consider disabling PAC files and auto-configuration in general within client web browsers.
    5. Internet Content Filter:
      1. A filter that is usually applied as software at the application layer and can filter out various types of Internet activities such as websites accessed, e-mail, instant messaging, and more. It is used most often to disallow access to inappropriate web material.
    6. Web Security Gateway:
      1. A type of security appliance that actively monitors data flows and scans for viruses, filters content, and act as data loss prevention (DLP) devices.
  2. Operation:
    1. When a client queries an HTTP server, the request instead goes to the HTTP proxy or proxy server.
    2. The proxy server forwards that request to the HTTP server, and stores a copy of the requested page in its memory (called caching) before forwarding it to the original HTTP client that requested it.
    3. All subsequent requests made for that site within a configured window of time will receive the cached copy of the site from the HTTP proxy server.
    4. This reduces the traffic load placed on the real HTTP server, and is much faster and more efficient than retrieving a new instance of the same site each time.
    5. By also using a content filter, specific website traffic can be filtered out. This increases security for your organization.
  3. Forward and Reverse Proxy
    1. Forward Proxy:
      1. The more common proxy server deployment type.
      2. When a client makes a request of the server, that request is forwarded to the proxy server
    2. Reverse Proxy:
      1. A less common proxy server deployment type.
      2. This type of proxy server retrieves resources on behalf of a client from one or more servers. These resources are then returned to the client, appearing as if they originated from the proxy server itself.