Request.Url.Host identical to Request.Headers["host"]?

Question

I've read conflicting things on this: In ASP.Net (and MVC), does the Request.Url.Host return the host header for the request? I've seen code that checks for Request.Headers["host"] first, then degrades to using Request.Url.Host if there is a problem, but I don't understand why this would be needed if they are identical.

Answer 1

They're not identical.

HttpRequest.Headers["Host"] gives you direct access to the client-to-server HTTP header.

HttpRequest.Url is rebuilt by ASP.NET and it does use the incoming request's Host: header by default, however there is an internal setting UseHostHeaderForRequestUrl, if this is set to false then ASP.NET will use HttpRequest.Headers["SERVER_NAME"] instead, but under certain circumstances it uses value of "127.0.0.1" instead.