dougv.com « The Web home of Doug Vanderweide

So you’re running a copy of FileZilla server on your Windows IIS Web server, you try to connect via your copy of FileZilla client, and you receive the most dreaded of all FTP error messages:

425 Can't open data connection. **

You try searching for “FileZilla server 425” and are sent to a Wiki page about network configuration. It tells you the problem is that your FTP server is behind a smart-aleck router or firewall of some sort, and that’s causing connection problems.

But that can’t be true, because you’ve been able to connect to this server before and you’ve done nothing to the network configuration since. Besides, other people can connect to your server; it’s just you who cannot.

You’re trusting. You do as the instructions say, changing IP addresses, fiddling with your server’s “active” and “passive” modes, playing with the server’s Windows Firewall / router settings — but nothing works, you simply cannot connect.

So you turn from the server’s network to your network. You run all the FileZilla client tests, play with all the settings, but still your computer will not connect to the remote server. What’s especially irritating is that your FileZilla client will connect to any other FTP site, but not your remote FileZilla server.

The solution is simple: Power down your router and cable / DSL modem, wait about 30 seconds, then power them back up. You’ll be able to connect once you’ve reestablished your network.

Your Router Is At Fault

If you use a Linksys, Netgear, DLink or similar home router to connect many computers to your cable / DSL modem, that router is almost always to blame for connection problems with FileZilla server.

Actually, I suppose you could blame FileZilla server as easily and be equally as right about the cause. Because it’s the two completely different approaches taken by router manufacturers and the programmers behind FileZilla server that really makes for the problem.

In defense of Linksys, Netgear, DLink and the like: The average home user is not a computer network engineer. But the process of linking together many different devices, from computers to printers to hard drives to stereos to DVRs, into a common, seamless network, is very difficult.

Therefore, whatever equipment the router manufacturers make, it has to be able to create very complex networks with virtually no intervention from the person doing the install (the easiest way to make things “foolproof” is to remove the fool from the equation). So home routers are designed to make getting all your equipment on the Internet and talking to each other as easy as plugging in cables. The tricks those home routers use to accomplish that goal aren’t always appropriate for every application. Such as, say, FileZilla.

In defense of FileZilla: FileZilla server is written by people who care about standards and who are intimately familiar with the arcana of FTP, an Internet standard older than the Web itself. As a result, FileZilla server is exact in how it speaks to FTP clients — including its sister, FileZilla client — and in the nature of what it expects FTP clients to say back to it.

Most other FTP server software is pretty lenient about the way an FTP client talks to it, but not FileZilla server. It expects honesty from your FTP client and if it doesn’t get it, it won’t play ball.

When Heads Butt, Power Down

So you have the problem of a router that, as a rule, needs to lie and hide things from other hardware / software in order to work properly, trying to talk to software that demands nothing short of the complete truth. The result is what we would expect from any dysfunctional relationship between a pathological liar and a stone-cold bitch: heads are going to butt.

After a while, your router basically spins a web of deceit so complex and long, that even it can’t follow the story any more. That’s when FileZilla says it’s had enough and refuses to listen any more.

The only way to resolve the problem is to detox the router back into reality. And you do that by simply turning off the power, waiting about 30 seconds for all the electricity to drain from it, then powering it back on.

(Remember that in most cases, when a router is connected to a cable / DSL modem, you should first power down the cable modem, then the router; to reboot, you should power up the router first, then the cable / DSL modem. This allows your router to grant DHCP leases to all attached equipment and the modem to properly address your router.)

Technically, what powering down the router really does is clear its NAT and DHCP tables, basically giving the router a blank slate from which it can formulate new lies to tell FileZilla server. And interestingly enough, that’s good enough for FileZilla server.

All links in this article on delicious: http://delicious.com/dhvrm/ftp-error-425-cant-open-data-connection-time-to-reset-your-router-and-modem

* I know I often say I don’t blog on Help Desk stuff, but this is so annoying and there’s so few places that tell you how to actually fix this problem, I decided to go ahead and put up this post.

**: Or maybe you’ve seen this:

(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> Connected, sending welcome message...
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 220-++++++++++++++++++++++++++++++++++++++++++++++
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 220-The FTP Server Welcomes You!
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 220-==============================================
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 220-Anonymous access prohibited
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 220-All activity logged
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 220 *********************************************************************
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> USER banana
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> 331 Password required for banana
(019697) 2/10/2009 10:05:37 AM - (not logged in) (101.92.82.255)> PASS ********
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)> 230 Logged on
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)> SYST
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)> 215 UNIX emulated by FileZilla
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)> FEAT
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)> 211-Features:
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  MDTM
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  REST STREAM
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  SIZE
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  MLST type*;size*;modify*;
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  MLSD
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  UTF8
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  CLNT
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)>  MFMT
(019697) 2/10/2009 10:05:37 AM - banana (101.92.82.255)> 211 End
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> PWD
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> 257 "/" is current directory.
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> TYPE I
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> 200 Type set to I
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> PASV
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> 227 Entering Passive Mode (123,456,789,1,10,203)
(019697) 2/10/2009 10:05:39 AM - banana (101.92.82.255)> LIST
(019697) 2/10/2009 10:05:50 AM - banana (101.92.82.255)> 425 Can't open data connection.
(019697) 2/10/2009 10:05:51 AM - banana (101.92.82.255)> disconnected.