IIS 7 how does http.sys know which request is for which application?

Question

I'm reading this and it says: "HTTP.SYS finds out the request is for which application. Each application hosted in IIS is mapped to an application pool." Based on what information in the request does http.sys decide which application is the destination?

Answer 1

I think ever since HTT 1.1 the URL requested is sent IN THE HEADER. So, Http.sys just looks at the request. Note that every application must be unique in the URL to a degree - and that is what HTTP.SYS uses.

Check https://en.wikipedia.org/wiki/List_of_HTTP_header_fields for a list of transmitted fields. The one you look for is "Host".

Answer 2

Portion (application pools, site bindings, and IIS sites/applications) of IIS configuration in applicationHost.config is shared with HTTP.sys, so that it can easily tell which IIS application should take care of an incoming request by URL and then locate the application pool associated with.

Hints:

• Utilize the Host header, destination IP address, and port number to determine which IIS site should be dispatched to.
• Analyze the path to see if an specific IIS application should be dispatched to.

References

• https://docs.microsoft.com/en-us/iis/get-started/planning-your-iis-architecture/understanding-sites-applications-and-virtual-directories-on-iis
• https://docs.jexusmanager.com/tutorials/binding-diagnostics.html