Implementing Proxy Server

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Many networks use proxy servers (or forward proxy servers) to forward requests for services (such as HTTP or HTTPS) from clients. If you’re planning to take the  SY0-401 version or the SY0-501 version of the Security+ exam, you should have a basic understanding of installing and configuring network components to support organizational security such as using proxy servers.

For example, can you answer this question?

Q.  Management at your organization wants to prevent employees from accessing social media sites using company-owned computers. Which of the following devices would you implement?

A. Transparent proxy

B. Reverse proxy

C. Nontransparent proxy

D. Caching proxy

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Transparent Proxy Versus Nontransparent Proxy

A transparent proxy will accept and forward requests without modifying them. It is the simplest to set up and use and it provides caching.

In contrast, a nontransparent proxy server can modify or filter requests. Organizations often use nontransparent proxy servers to restrict what users can access with the use of URL filters. A URL filter examines the requested URL and chooses to allow the request or deny the request.

Many third-party companies sell subscription lists for URL filtering. These sites scour the Internet for web sites and categorize the sites based on what companies typically want to block. Categories may include anonymizers, pornography, gambling, web-based email, and warez sites. Anonymizers are sites that give the illusion of privacy on the Internet. Employees sometimes try to use anonymizers to bypass proxy servers, but a proxy server usually detects, blocks, and logs these attempts. Web-based email bypasses the security controls on internal email servers, so many organizations block them. Warez sites often host pirated software, movies, MP3 files, and hacking tools.

The subscription list can be loaded into the proxy server, and whenever a user attempts to access a site on the URL filter block list, the proxy blocks the request. Often, the proxy server presents users with a warning page when they try to access a restricted page. Many organizations use this page to remind users of a corporate acceptable usage policy, and some provide reminders that the proxy server is monitoring their online activity.

Proxy servers include logs that record each site visited by users. These logs can be helpful to identify frequently visited sites and to monitor user web browsing activities.

Remember this

A proxy server forwards requests for services from a client. It provides caching to improve performance and reduce Internet bandwidth usage. Nontransparent proxy servers use URL filters to restrict access to certain sites, and can log user activity.

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Reverse Proxy

A reverse proxy accepts requests from the Internet, typically for a single web server. It appears to clients as a web server, but is forwarding the requests to the web server and serving the pages returned by the web server. The figure shows how a reverse proxy server is configured to protect a web server. Note that this configuration allows the web server to be located in the private network behind a second firewall.

Proxy Server

 

Reverse proxy server

Imagine that Bart wants to access http://gcgapremium.com. He types the URL into his browser and it connects to the reverse proxy server. The reverse proxy server connects to the web server and retrieves the web page. It then sends the web page to Bart. A reverse proxy server caches the web pages just as a forward proxy server does, so it can improve the overall web site performance.

The reverse proxy server can be used for a single web server or a web farm of multiple servers. When used with a web farm, it can act as a load balancer. You would place the load balancer in the DMZ to accept the requests and it then forwards the requests to different servers in the web farm using a load-balancing algorithm.

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Application Proxy

An application proxy is used for specific applications. It accepts requests, forwards the requests to the appropriate server, and then sends the response to the original requestor. A forward proxy used for HTTP is a basic application proxy. However, most application proxies are multipurpose proxy servers supporting multiple protocols such as HTTP and HTTPS.

As a more advanced example, imagine you buy a book from Amazon and Amazon ships it via United Parcel Service (UPS). Later, you check your account to see the status of the shipment. The Amazon web site sends a query to a UPS application proxy for the status. The UPS application proxy provides the status in a response. Internet applications exchange data this way using application programming interfaces (APIs). For example, UPS specifies the format of the request in an API. If the application proxy receives a properly formatted and valid request, it provides an answer.


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Q.  Management at your organization wants to prevent employees from accessing social media sites using company-owned computers. Which of the following devices would you implement?

A. Transparent proxy

B. Reverse proxy

C. Nontransparent proxy

D. Caching proxy

Answer is C. A nontransparent proxy includes the ability to filter traffic based on the URL and is the best choice.

A transparent proxy doesn’t modify or filter requests.

A reverse proxy is used for incoming traffic to an internal firewall, not traffic going out of the network.

Proxy servers are caching proxy servers, but won’t block outgoing traffic.

See Chapter 3 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide

or

See Chapter 3  of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide

for more information on implementing a secure network.

2 Comments

  1. Darril,

    Thanks so much for your SY0-401 study guide and updates you are sending me with questions, solutions, and blogs. I plan to take the SY0-401 exam in the next two weeks, I noticed in this particular blog you referenced the study guides for both SY0-401 and SY0-501 regarding proxies. I bought the former study guide but not the latter. Chapter 3 of SY0-401 does not appear to provide the detailed explanations of proxy servers that Chapter 3 of SY0-501 apparently does. I have read your SY0-401 study guide several times now and have taken all the quizzes in it. I am concerned there may be other examples in which I will be taking the final exam for SY0-401 but the actual details for correct responses are in the SY0-501 study guide. I appreciate any comments you may have.

    Thanks in advance,

    William

    • The blog starts with
      “If you’re planning to take the SY0-401 version or the SY0-501 version of the Security+ exam, you should have a basic understanding of installing and configuring network components to support organizational security…”

      The 501 objectives specifically mention transparent and nontransparent proxies. The 401 objectives do not.

      If you want additional materials than you might want to invest in one of the online study packages such as this one.

      Gratefully, we hear from people almost every day (including several notes I’ve seen today) letting us know that people have passed the Security+ exam (both versions) using the study guide and/or online materials.

      Good luck on exam day.

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