When do we need to register a .Net dll and a COM dll?

I am not clear about when do we need to register dlls? I guess we register .net dll if it needs to be accessed from a COM dll and we register COM dll if it 开发者_如何转开发needs to be accessed from a .net dll. Is this correct? Please correct me if I am wrong. Thanks in advance for any clarifications.

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A COM dll always needs to be registered.

If the .Net DLL exposes a COM interface then it to needs to be registered.