asp.net webforms modules and handlers section - is remove required? - asp.net

Question

Below is the default configuration for ASP.NET webforms web.config for specifying handlers and modules under IIS 7 (.5)
When you add custom modules and handlers, I would like to know if remove name ="custom module" is required before adding the module entry. I couldn't find much information on this on whether or why remove is required. I saw some examples where they didn't have removes.
The reason why I'm asking is I vaguely remember reading something about module references will keep adding same entries every time instead of having just one, eventually failing. But I can't find that anywhere now.
If someone can confirm, it will be much appreciated.
<system.webServer>
<validation validateIntegratedModeConfiguration="false"/>
<modules>
<remove name="ScriptModule" />
<add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
</modules>
<handlers>
<remove name="WebServiceHandlerFactory-Integrated"/>
<remove name="ScriptHandlerFactory" />
<remove name="ScriptHandlerFactoryAppServices" />
<remove name="ScriptResource" />
<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode"
type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode"
type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add name="ScriptResource" preCondition="integratedMode" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
</handlers>
</system.webServer>

Answer 1

Taking a look in the MSDN, but in the <add> page, you will read this:
The <add> directives are processed in top-down, sequential order. If
two or more <add> subdirectives specify the same verb/path
combination, the final overrides all others.
Based on that, in order for a <add> directive to be overridden, it must have the same verb/path combination. If they do not match, both directives are active and that might cause conflict issues.
Removing the existing directives before declaring your own is a good practice to avoid any conflicts.
Edit: Your application inherits settings from other web.config files as well (See here for more info). Those can be the machine.config, the root web.config etc. Those files can contain module and handler declarations as well. Adding <remove> helps you avoid any conflicts with those files.