How to configure the web.config to allow requests of any length

Add the following to your web.config:

<system.webServer>  <security>    <requestFiltering>      <requestLimits maxQueryString="32768"/>    </requestFiltering>  </security></system.webServer>

See:

http://www.iis.net/ConfigReference/system.webServer/security/requestFiltering/requestLimits

Updated to reflect comments.

requestLimits Element for requestFiltering [IIS Settings Schema]

You may have to add the following in your web.config as well

<system.web>    <httpRuntime maxQueryStringLength="32768" maxUrlLength="65536"/></system.web>

See: httpRuntime Element (ASP.NET Settings Schema)

Of course the numbers (32768 and 65536) in the config settings above are just examples. You don't have to use those exact values.

In my case ( Visual Studio 2012 / IIS Express / ASP.NET MVC 4 app / .Net Framework 4.5 ) what really worked after 30 minutes of trial and error was setting the maxQueryStringLength property in the <httpRuntime> tag:

<httpRuntime targetFramework="4.5" maxQueryStringLength="10240" enable="true" />

maxQueryStringLength defaults to 2048.

More about it here:

Expanding the Range of Allowable URLs

I tried setting it in <system.webServer> as @MattVarblow suggests, but it didn't work... and this is because I'm using IIS Express (based on IIS 8) on my dev machine with Windows 8.

When I deployed my app to the production environment (Windows Server 2008 R2 with IIS 7), IE 10 started returning 404 errors in AJAX requests with long query strings. Then I thought that the problem was related to the query string and tried @MattVarblow's answer. It just worked on IIS 7. :)

Something else to check: if your site is using MVC, this can happen if you added [Authorize] to your login controller class. It can't access the login method because it's not authorized so it redirects to the login method --> boom.