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Good day,

I'm having problems with the ftp server I've just set up. I've already managed to configure my modem and wireless router to open up port 21 and setup ftp in my server. But It seems that when I try to connect to it when I'm in the same network as the server via URL, (ftp://mydomain.com) it redirects me to the modem's web interface. But then when I try to connect to it outside the network using a different internet connection. It succeeds. It also succeeds when I'm in the same network and I go to ftp://192.168.., the server's local IP. Am I supposed to adjust something in the modem or router? Or is this a different problem altogether?

BTW I'm using Windows Server 2008 r2 as my server's OS and using IIS for ftp.

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2 Answers

This is depending on the model of your firewall. I know Sonicwalls you have to set it up for a loop from your LAN to WAN and then let traffic back into the LAN.

Here's a little more info

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The problem you have is with your DNS. Clearly the DNS is configured to provide the public IP address for your FTP site. And because of that your machine wants to send the traffic out through the default gateway. It then comes back (since the server sits behind the same gateway) and because no port forwarding has been defined, you hit the gateway's web interface (which, by the way, should be locked down. Is it?)

There are a number of ways out of this. You could just enable some port forwarding on your modem, which forwards incoming traffic for HTTP and FTP to your Windows server. Most likely that is the simplest solution.

Another solution would be to define a separate DNS entry, e.g. ftp.localdomain, in the DNS on the Windows Server, which resolves to the internal IP address, and then ensure that your client uses the Windows Server for DNS (but in that case you must also ensure that the Windows DNS Service forwards unresolved queries to the ISP's DNS servers).

Another possible solution is to run split DNS, where DNS requests from public addresses will get public IP addresses, and internal DNS requests will resolve (for the same host/service name) to internal IP addresses. Whether you can easily do this, depends on your DNS and network configuration.

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