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Posted 11 Mar 2003

Domain Forwarding with IHttpHandler

, 9 Sep 2003
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Use HttpHandlers to forward the user to different webpages depending on the requested hostname (domainname).


In this article I describe how to use a custom HttpHandler as a domain-forwarder.


With the Hostheader feature in IIS you can map many hostnames to one IP-Address. For example your IIS Server has the IP-Address You or your ISP has some A-Records for this IP-Address.


Now, you have configured a website in IIS which responds to all these domains. The following image show a sample IIS configuration.

All requests to, and target the same website. Often you have to do such configurations because the amount of public IP-addresses is limited.

At this point you want to provide the user a different webpage depending on the used domain name. This sample application will provide a simple solution for this problem.

Using the code

Create a class in your ASP.NET application which implements the IHttpHandler. You have to implement one method and one property:

  • public void ProcessRequest (HttpContext)
  • public void IsReusable

Here is the sample code:

public class DomainHandler : IHttpHandler
    /// Implementing IHttpHandler
    public void ProcessRequest(HttpContext context) 
        // Extract the host name from the request url
        // an look up the redirect url in the Web.config
        String redir = ConfigurationSettings.AppSettings
        if (redir != null)
            // check for valid redirect url, preventing loops
            if (RedirectIsValid(redir, context.Request.Url))
                // redirect the user to the url found in web.config
                context.Response.Redirect(redir, true);
                // display an error.
                   color=red>Error invalid DomainHandler 
                   <b>Please check your Web.config 

    // prevents possible redirect loops
    // it is not allowed to have an redirect url targeting its self
    private bool RedirectIsValid(String redir, Uri currentUri)
        String val1 = redir.ToLower();
        String url = currentUri.AbsoluteUri.ToLower();
        String host = currentUri.Host.ToLower();

        if (val1 == url) { return false; } 
        if (val1 == ( "http://" + host)) { return false; }
        if (val1 == ("http://" + host + "/")) { return false; }
        if (val1 == host) { return false; }
        if (val1 == (host + "/")) { return false; }

        return true;

    /// Implementing IHttpHandler
    public bool IsReusable
            return true;

Points of interest

I decided to store my URL mappings in the web.config file as key-value pairs in the appSettings Section. Additionally you must register the new HttpHandler in your web.config file.

Sample web.config file is provided here:

<?xml version="1.0" encoding="utf-8" ?>
<!--<span class="code-comment">
Use as keys your full qualified host names.
As Value you provide a absolute url, you want to redirect to.
<add key="localhost" value="http://localhost/DomainForward/target1.htm" />
<add key="" value="" />
<add key="" value="" />






<add verb="*" path="Default.aspx" 

    type="DomainFilter.DomainHandler, DomainFilter" />



In the path attribute in the httpHandlers section you specify a really existing filename which matches your "IIS-Defaultpage-Configuration".

In my sample application for simplicity I used a subweb, the default in Visual Studio. In a real world example, you would install the application in the root-web.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Andi Fleischmann
Web Developer
Germany Germany
No Biography provided

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Comments and Discussions

QuestionBind Domain to Application Pages Pin
Morteza M17-Nov-12 4:05
groupMorteza M17-Nov-12 4:05 
What about this?
Lets check the scenario:

I have a tbl_Users and maped http://mydomain/[username] to each users profile using Routes. they have some Routed pages in their profiles (like contacts, etc.)


Now I need to let them register domains for themselves and map their domains to their profile pages. (I don't want to forward domain! I want to see their own url) == search in db ==>[aUser]
AND SO ==search in db==>[aUser]/contactus
I kept their domain lists in DB. I know that I have to Add their domains to IIS (Or domain Alias to

I want to let them work in their domain like their profile in main domain.

What's the solution in ASP.NET 4 ?

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