FTP fails when opening ASCII mode

I am using Serv-U ftp server. I connect fine. User/pass authentication is no problem. But when I try to get a directory listing, all I see is this:

ftp> dir
200 PORT Command successful.
150 Opening ASCII mode data connection for /bin/ls.

and it never comes back with a directory listing. It just times out. What's up?
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DrDamnitAsked:
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neteducationCommented:
The back-channel (ftp-server connecting back to your ftp-server) does not come through.

Some real bad Firewalls that dont know about FTP block this (Is there a firewall between the server and the client?)

Try to use passive mode, that should help.
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neteducationCommented:
oops typo... backchannel = ftpserver connecting back to your ftp-client
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kneHCommented:
Either turn passive mode on or off should sort it.

Also try the "bypass proxy" option if passive doesn;t work.
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DrDamnitAuthor Commented:
My firewall has ports 21 and 1400-1500 forwarded to my ftp server. What is the back channel number?
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kneHCommented:
Usually one lower than the port number.

But I really suggest fiddling with the passive toggle
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neteducationCommented:
the backchannel is going from the server to the client, so it's not so important whats open from outside to the server, but from the server to outside. Do you have any limitations there ?
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DrDamnitAuthor Commented:
No, there aren't any limitations. It's strange. Funny thing is, it worked before, but the only thing that has changed is the router has been restarted. No server properties have changed. I have another FTP server running on the same machine just on a different port, and it works fine. They have worked together before...
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kneHCommented:
I can understand your nick now then ;)

Btw if you wanna see which ports a program uses get fport.
it'll show you servu uses a port somewhere in the 40000's and one either on 5555 or 4500

http://freedom.dicea.unifi.it/ftp/pub/nt/fport.exe
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DrDamnitAuthor Commented:
It wanted another port. Greedy server program. You like my handle? I find it rather fittng. It was either that or F-Bomb Ph.D.
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