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404 Not Found Error: What Is HTTP 404 and How It Functions

404 Not Found Denfinition


404 error is one of the most commonly seen web errors and it is also one of the most classic errors in the computer world. 404 not found is a standard HTTP return code. To put it simply, 404 error page emerges when invalid URL is inquired. As a matter of fact, IIS(Internet Information Services) on the server end checks for corresponding web information according to the input URL before displaying content. In the event that no corresponding information is found to fit the input URL, IIS delivers 404 error page to end user through the server, telling user that no web information has been found for the inquired URL. Most PC users do not know the truth about 404 Page Not Found error and thus generate panic when coming across it. In the following paragraphs, VilmaTech Online Support will inform you the reasons to trigger HTTP 404, the advantage of 404 error page and instruction to resolve 404 Not Found related issues. Should you have questions in the middle of the reading, please feel free to get quick answers by starting a live chat here.

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Situations that Trigger 404 Error Page and Solution

VilmaTech Online Support would like to hereby list down several situations that bring HTTP 404 to surface so as to convince users that 404 Not Found is not fault phenomenon but a kind reminder of inaccessibility to certain site.

Situation NO.1 – wrong URL is requested to arouse 404 Not Found message from IIS.

Situation NO.2 – the inquired web page has been deleted from server; this happens a lot to the pages published long ago in forums due to the guarantee of the rational use of server resource.

Situation NO.3 – the access to inquired web page is prevented by DNS settings; such situation can be solved by adopting proxy server.

Situation NO.4 – wrong spell in inbound link.

Situation NO.5 – web document is renamed or moved to another place.

Situation NO.6 – generative rule on URL is changed.

To sum up the above three situations in terms of professional, HTTP 404 is caused by the incapability of visiting web site on the requested port, the locking strategy on extend proxy service stops request and MIME deters request. To resolve 404 error, the web page creator should restore web document’s location and re-configure NW service (network service); For surfers, there is limit to what you can do. Checking the input URL for correctness is recommended. In fact, 404 error can be used to optimize certain web site and retain potential customers if it is utilized properly.

Advantage of HTTP 404

404 Not Found error may not be wanted by surfers, but it can be a present for website builders as well as SEO editors. 404 error page was created to optimize web site and enhance user experience. A properly configured 404 error page manages to prevent 200 error triggered by incorrectly configured server and 302 error incurred by the application of Meta Refresh. By setting 404 error page, user can be directed to another site when page access error occurs, which decreases the number of dead links because of it and optimize the rankings of the site to which users are redirected just like Yahoo does.

yahoo 404 error

Therefore, optimizing 404 error page is a smart move for site builders. Below is the instruction offered by Patricia Howard to set 404 error page. If you have any question about setting 404 error page, you are welcome to get quick answer by starting a live chat window.

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Instruction to Resolve 404 Not Found Related Issues

Steps to resolve 404 Not Found error due to the change in path.

1. Hold and press Win key and R key together to bring up Run box.
win+r key combination
2. Type “inetmgr” and hit Enter key will prompt to you IIS manager.
IIS manager
3. Make 404 error code to point to a dynamic page and employ 301 permanent redirection.

Steps to set 404 error page on Apache server and IIS/.net

On Apache Server

1. Add “ErrorDocument 404 /Error.html” to .htaccess file under root directory.
.htaccess file
2. Build a simple html404 page and name it as Error.html.
3. Put Error.html under web root directory.


  • Do not direct 404 error page to homepage; otherwise search engine spider will ask Data Center to remove your homepage.
  • Do not use absolute URL; otherwise 302 or 200 error code will occur, which means the URL is valid and that the URL will be included in index database; as a consequence, duplicate pages emerge and this will definitely lead to authority degrading or even permanent removal.

On IIS/.net

1. Modify the settings to root directory of Application Program by adding the below quoted content into web.config:
web.config file to customize 404 error page

<customErrors mode=On defaultRedirect=error.asp>
<error statusCode=404″ redirect=notfound.asp />

Tip: “error.asp” refers to the default 404 error page by OS, and “notfound.asp” refers to customized 404 error page.

2. Add the below quoted content to the customized 404 error page (notfound.asp):

<% Response.Status = 404 Not Found %>

Steps to optimize 404 error page

1. Add the below quoted content to web.config:

<customErrors mode=”Off”  defaultRedirect=”[the site to which you want to redirect].aspx(tip: if it is developed by MVC, then add /Controllers/action ) ” >
<error statusCode=”403″ redirect=”ditto”/>
<error statusCode=”404″ redirect=”ditto”/>
<error statusCode=”500″ redirect=”ditto”/>
<error statusCode=”502″ redirect=”ditto”/>


To sum up:
404 Page Not Found error is made to inform users that the requested URL is no longer existent. Obviously, HTTP 404 is neither caused by virulent affections nor a symptom of system failure. On the occurrence of incapability of visiting web site on the requested port, request prevention by locking strategy on extend proxy service and MIME, 404 error page emerges to tell that certain site is gone for good. Though this is its primary function, 404 error page is also surprisingly beneficial to SEO and user experience enhancement. However, any wrong configuration to HTTP 404 would cause 302 and 200 error code, which would result in duplicate content and that would impose adverse impact on a web site. The above instructions are mainly about setting 404 error page, optimizing HTTP and resolving 404 Not Found error due to the change in path. Should you run into difficulty due to deficient knowledge, it is advisable to contact VilmaTech Online Support and get professional help after technical analysis to resolve 404 issue on concrete situation.

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