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I have a Windows Server 2019.

The server has 3 NICs.

  1. NIC is the internal network.
  2. NIC is an external router into the internet with a defined standard gateway (FritzBox)
  3. NIC is an separate external IP address where I want bind an IIS to. With its own standard Gateway.

I created a new site in my IIS that is bound to the third NIC.

But it seams that when I make an request from the outside, the server answers via NIC 2.

Of course the routing is set with a low metric for NIC 2 and a higher metric for NIC 3. Because I want that all normal traffic uses NIC 2. and not NIC 3.

Edit: NIC 3 is only used by http and https (so I only have the IIS listening to it).

The problem:

  • Contacting the IIS via NIC 1 (using the IP of NIC 3) works.
  • Contacting the IIS via NIC 3 (from extern) doesn't work.

Edit 2:

  • Setting the metric of NIC 3 below the metric of NIC 2 causes the IIS to respond from intern and extern. But all traffic now runs via NIC 3 (I don't want this)
  • Setting the metric to automatic or NIC 2 below NIC 3 causes the problems named above.
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  • What service are you talking about? Typically in a protocol like HTTP you have one TCP connection and the answer is sent through the existing atacap connection so that it automatically reces the system that had sent the request. Or do you mean by answer the IP packets so that even the TCP handshake fails (that would be long time before an actual request reaches the server).
    – Robert
    Jan 12, 2022 at 21:05
  • applications cannot control the interface their traffic leaves through. that is determined by the routing table. an app can control what interface it listens on, but the network stack will attach the egress port to the interface defined by the route table, and there isn't anything you can do about that. Jan 12, 2022 at 23:18
  • It only about http and https (IIS), see edit.
    – xMRi
    Jan 13, 2022 at 13:56

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