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My old modem just died, so I borrowed a friend's, and I put it in between the router and phone line, logged into it, setup my own login credentials .. and away she went.

It was working fine for internet sites, Skype, etc, etc, but no FTP client will seem to work. This includes FireFTP (Firefox plugin), Aptana FTP, WinSCP and FileZilla.

Could it be that this new modem has certain ports blocked? It is a SpeedStream 4200-Series.

Thanks

UPDATE

It seems to halt in FireFTP with this message last in the log

227 Entering Passive Mode (70,87,76,162,22,215) MLSD

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3 Answers 3

up vote 2 down vote accepted

Just make sure port 21 isn't blocked. There are a couple of Google results for this same issue suggesting to telnet to the FTP servers.

You've done most of the troubleshooting already - you know the modem is the problem

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Forwarding port 21 to a machine is for FTP servers. Clients do not need to listen to port 21. –  Arjan Aug 18 '09 at 8:05
    
Yup, don't know what I was thinking –  Ciaran Aug 18 '09 at 8:10
    
Meanwhile we also know that port 21 was not blocked, as some FTP commands were going over the wire. But well, it magically somehow solved the problem, so hurrah ;-) –  Arjan Aug 18 '09 at 8:48
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You may need to use Passive FTP. (For, when using Active FTP, your computer needs to open up ports to accept incoming traffic as well, which may be blocked by the router/modem. Not all servers like clients that use Passive FTP though.)

EDIT: Even using Passive FTP may yield problems because routers often rely on NAT, which changes ports on the fly. However, the FTP protocol uses PORT and PASV commands, which tells the other side which ports are being used. Here, the router messes up when changing the ports. So, a good router must know that it is handling FTP and actually change the PORT and PASV commands to make up for the port changes.

A DSL modem often has a router built-in, though it may not have a switch (or, a hub in the old days) in the same housing as well. So, a DSL modem often supports multiple computers, but needs an additional switch to actually allow for connecting multiple wired computers. Just counting the ethernet ports does not tell one if a device is a router or not.

According to the user manual, the Siemens SpeedStream 4200-Series has a built-in router. So, you are now using two routers. When using UPnP to allow your software to request to configure port mappings, then FTP may in fact work, but using two routers may mess up things a bit. You may also encounter problems for Instant Messaging (or: video or audio during Instant Messaging), or for certain games. (Note that enabling UPnP may also allow trojan horses (or viruses) to request port mappings, so if not really required one could leave it to "off", or to some safe settings like "discovery only".)

(Like MarkM suggested you may be able to put the first router into "bridge mode". That kind of connects your second router to the internet directly. When using the router-functionality of the first router, then you can set up the second router in "bridge mode" instead. In either case, one router should suffice and avoid problems. It may be a bit hard to get done though. To ensure your friend did not leave some undocumented configurations in the SpeedStream, considering resetting it to factory settings as well.)

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I don't think I'm using 2 routers - the modem only has a power, phone line, ethernet and USB inputs in the back, and is definitely not wireless. If it were a router, it should have a few more ethernet inputs right? –  alex Aug 17 '09 at 22:42
    
Though your problem has been resolved, I added some more about the router functionality in my answer for the archives. –  Arjan Aug 18 '09 at 7:10
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Your new modem may also be a router. Most home routers have a 4-port switch built into them with a WAN link for the Internet connection, but this isn't always the case. I've seen a few modems with a single Ethernet port that are actually routers as well. If you're behind two NAT boundaries (which is the case if you're behind the default config for two home routers) all kinds of nonsense happens.

I'd grab the manual online for your model and make sure it doesn't double as a router, and if it does, find out how to put it into bridged mode.

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