"felix" <felix(NO-SPAM)@eastop.com> wrote in message
news:%23MYqgj4$EHA.3924@TK2MSFTNGP15.phx.gbl...
>I found out that IIS will return its private IP when it responses to PASV
>mode, instead of using its public IP address. However, it just happens to
>one of my client site only. I have another IIS FTP server in another site,
>and it can return the correct public IP in responding to PASV command, and
>therefore passive mode can be used successfully.
>
> So what judges IIS to respond with a private or public IP?

> IIS always responds with its private IP.
>
> Actually, to be more pedantic, IIS always responds with the IP that the
> client connected to it at. IIS doesn't know about private or public, it
> just knows "I received a TCP connection on a.b.c.d, so that's what I'll
> use in PASV responses".
>
> What translates this is the NAT router - the device where you actually
> distinguish between those "private" and "public" addresses.
>
> If your NAT router isn't translating these, there are two common reasons:
> 1. It isn't up to date with current firmware - as far as I am aware, all
> NAT routers can be updated to handle FTP traffic on port 21.
> 2. Your FTP server isn't bound to port 21 on both sides of the NAT. As a
> result, your NAT doesn't know that it's supposed to translate FTP
> packages.
>
> Alun.
> ~~~~
> --
> Software Design Engineer, Internet Information Server (FTP)
> This posting is provided "AS IS" with no warranties, and confers no
> rights.
>