Why does 'localhost' in web references cause SocketExceptions?

I have two .net web services deployed to the same IIS server using SSL, one that references the other.

If I set that web reference to 'localhost', some calls fail with this exception:

System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> System.Net.WebException: Unable to connect to the remote server ---> System开发者_JAVA技巧.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it

If I set it to the actual machine name, it works.

Why?

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I suspect you'll find that IIS is configured to listen for requests on the "real" network interface but not on the loopback adapter.

You should be able to see this with a plain browser - try going to https://localhost on the box and see what happens.

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The 127.0.0.1 possibly can resolve the problem. Why? I dont know- get from the experiments.