We are using Solar Winds Serv-U FTP on one of our servers - On this server we also have IIS hosting a few websites (lets call it a.com and b.com)

We currently have Serv-U FTP (web interface) on b.com:8084 which runs fine!

What we would like is to have it serving on FILES.b.com:80 however when ever I try this it says port 80 is in use (it shows an error 404 when I access that page).

I think IIS is using the subdomain but I can't find where to turn it off... Can anyone advise?


Windows Server 2012 R2

IIS version 8

Serv-U version (64bit)


You can have different server software handle the same port number of different subdomains, if the subdomains have different IP addresses only.

In the end, the web browser connects to the IP address and port number, not to the domain name. So if the IP address and port number is the same for different (sub)domains, the operating system on the target server machine cannot distinguish the requests to route them to a different server software.

  • but cant i tell IIS not to resolve to that specific subdomain? – Gaza Jan 26 '16 at 12:02
  • What does it mean "IIS not to resolve"? – Martin Prikryl Jan 26 '16 at 12:03
  • Well when i go to files.b.com its showing the error 404, which IIS is serving - isnt there anyway for IIS not to do anything when someone goes to files.b.com so Serv-U picks it up instead? or will it just be easier to purchase a second IP address and point the subdomain to that? – Gaza Jan 26 '16 at 12:06
  • It's the operating system that passes the connection incoming on a specific IP/port combination to a server software. There's no way fallback mechanism. And there's even no way to tell what domain the webbrowser wants at this point. That information is in the HTTP header only, which the OS does not understand. Only the webserver understands that. So what you ask for would be possible only if IIS and Solarwind servers had some mutually agreed mechanism to route the requests between each other. But there's nothing like that. – Martin Prikryl Jan 26 '16 at 12:12
  • ah! so even a second IP address just for Solarwinds Serv-U wouldn't work? – Gaza Jan 26 '16 at 12:14

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