The purpose of this guide is to provide examples of subtle problems caused by web filters and how to troubleshoot these issues. Brief comments on how to build a business case to remove blocks on a particular web site.
This guide takes no position on the appropriateness of web filtering.
If your web filter product is imposed by your parent agency, you probably don't have the ability to remove a site from filtering so that everyone in your enterprise can view the site without preconditions such as logging into a waiver page. But don't lose heart. You may be able to persuade your parent agency to remove the site from filtering if you follow these suggestions.
I. THINK ABOUT WHY YOUR AGENCY FILTERS
The reason your parent agency has implemented filtering should inform the approach you take in asking for a site to be unblocked. Are they blocking to save bandwidth, to block pornorgraphy, or out of concern that employees are wasting time?
II. THINK ABOUT WHY YOU NEED THIS PARTICULAR WEB SITE
Before you approach your parent agency to have a site unblocked for yourselves and/or the larger organization, ask yourself if you have alternatives that are not blocked. For example, The Computer Science Class CS50x videos are usually watched from YouTube, which many organization block. But if you take the course through EDX.org, then alternative download links from cs50.net are provided. Chances are good that your web filter won't block cs50.net even if it does block YouTube.
If you can get by without asking for a site to be blocked, that is what your IT will expect you to do. The best IT departments will find these alternatives for you, but don't coun't on that.
III. PREPARE YOUR CASE
Once you understand why your parent agency is filtering in the first place and have documented why you don't have a suitable unblocked alternative, you can move forward. Here's an example from the Alaska State Library:
We needed a hosting solution for our video that could be viewed by State Employees and students in schools. We did not have a complete video streaming solution in house. YouTube is not only blocked by the State of Alaska, but also by many school districts around the country. Additionally the State of Alaska filters out of a combination concern over bandwidth usage and to keep employees from wasting time and state bandwidth on sites deemed "not business use" for state employees. So we immediated discarded the idea of asking for YouTube.
A colleague in the Department of Education and Early Development (EED) had received permission to post to SchoolTube, one of a number of educational hosting sites trying to be "YouTube for Teachers." From this colleague and other sources we learned that SchoolTube was permitted in most school districts around the nation. Additionally any video posted to SchoolTube had to be moderated by an institution's staff. So content was fairly education focused. Despite this, only EED employees had access to SchoolTube.
So we went to our Commissioner and asked him to go to Central IT with a request to allow other state agencies access to SchoolTube. Our department's talking points were:
Our request was granted and now virtually anyone can watch videos posted by the Alaska State Library or the Alaska OWL Project. We got our exemption in part because we did our homework. We demonstrated we had a need. We showed that we tried to meet that need within our enterprise. We identified an alternate resource that addressed the State's bandwidth and "time wasting" concerns.
Those of us with web filtering have seen the "blocked by filter" page. Sometimes this page will include instructions how to unblock the filter, but not always. We come to believe that either pages will come up as intended or we'll get the "blocked by filter" page. But sometimes we get something in between. A page is granted to us, but looks very strange, like the front page of the news site www.theverge.com:
If you were able to turn off your filtering, you'd see that The Verge should actually look more like:
In other cases, a page may start to load correctly, but freeze. This happened with Mango Languages loaded onto our research computers, which have a partial block on them.
In neither case, did our web filtering software offer an old fashioned "filter blocked page" alert.
The key in almost every "subtle filter error" is to get at a page's source code and look for content that doesn't match the URL you are visiting. Staying with our example of The Verge, let's look at the source code:
The lines circled in red where the links end in ".css" are called style sheets. Style sheets control a web page's look and feel. Notice that the style sheets for theverge.com don't come from the site itself, but from a site called cdn3.sbnation.com. There's nothing wrong with a site's style sheets coming from a different server. Any web page can have content from anywhere. But in this case, cutting and pasting http://cdn3.sbnation.com into our web browser brings up a "filter blocked page" that shows the page was blocked because it is in the "sports" category. For us, this page gives us the opportunity to enter our id and password to waive the filter. Once we do so, we can reload theverge.com and it will appear normally.
Examining the page source for Mango Languages revealed that it needed content from googleapis.com and amazonaws.com to load correctly. Because this problem was on our research computers whose filters we directly controlled, we simply added googleapis.com and amazonaws.com to our "white list" and Mango Languages began operating normally on those machines.
If your block page doesn't give you the category that a site was block under, try searching [(name of web filter) check link] in your favorite search engine. This ought to yield a "URL Checker" that you can use to see how your web filter categorizes your problem URL. For instance, if your filter is McAfee Web Gateway, you can check a link's category at http://www.trustedsource.org/urlcheck/.
How you can get to a page's source code varies from browser to browser. Below are links to pages that explain how to get to your source code.
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