> -----Original Message-----
> From: Angus Robertson - Magenta Systems Ltd
> Sent: 07 September 2010 09:47
> To: firstname.lastname@example.org
> Subject: Re: [twsocket] PASV fallback to public IP
> > Some FTP servers return wrong IP for PASV command (private
> instead of
> > public). In such cases, obviously, FTP component can't
> connect to the
> > server.
> This is not really an FTP server issue, but a poorly designed
> NAT router that has not replaced the private IP address with
> a public IP.
> > Filezilla is smart enough to detect this and switch to public IP,
> > instead:
> Detecting the wrong address is easy, but whether replacing it
> with a public address will do anything useful is more
> debatable since the NAT router may not know which private IP
> address is the intended destination of the incoming TCP connection.
> NAT routers have to be designed to understand the FTP
> protocol, and parse the control channel for private IP
> addresses and forward connections appropriately. Normally
> this is all hidden and you never know it's happening.
> Do you have a specific example of a live public server
> returning a private IP that we can test? It will be very
> difficult to set-up, since it needs a crappy NAT router.
As a FileZilla client and server user of some years.
Servers that return a Private (LAN) IP in a Passsive Mode parameter
value, are probably misconfigured by their owners, rather than any
deficiancy in the routers used.
F'Zilla can only "detect" your WAN IP, if you point it to a suitable
external site/service that will report back your WAN IP. Sadly, not all
of them do it in a way F'Zilla can reliably handle. You could use a
local to you service, that in turn polls your router setup pages to find
the WAN IP currently in use, but every router is different.
If you have a dynamic WAN IP as most home users do, you can use an
external service such as DynDns so you can have a regular "domain name"
who's resolved IP follows your actual IP as it changes from time to time
(with a short delay...)
Then, in F'Zilla (and I guess in any ICS created server) you can find
your outside (WAN) IP, by doing a DNS query on yourself (in FZ, you put
your domain name in the Passive Mode Settings dialog, "Use the following
IP" field) that in turn will return your current WAN IP address, that is
then used as part of the client Passive mode setup protocol.
Or, you ask your ISP for a fixed IP account. :)
The only thing you need to do to any routers in line, is make sure that
their port forwarding rules are setup, so that *All* the FTP Data
port(s) you use, are passed to the machine on your LAN that is running
the server. The client of course, does not need to make any such
adjustments, they only ever initiate outgoing connections, so no port
forwarding needs to be done.
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