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Active Mode access to Win98 FTP server behind Linksys BEFSX41 router

Posted on 2003-12-05
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Last Modified: 2013-11-30
I have a home LAN behind a cable modem and Linksys BEFSX41 router. One of the computers on the LAN is running Win98 and an FTP server, currently GuildFTPd.  My cable ISP has assigned me one external IP address, which gets an outside user to the cable modem/router.

The machines on my LAN are all assigned static IP addresses, in the 192.168.x.x range. In the router (this is a NAT type router with UPnP features), on the UPnP Forwarding page, I've forwarded the FTP port (assumed by the router to be 21, and not changeable) to the FTP server's static IP.

With this configuration, Passive Mode access to the FTP server works, both from the outside and from the inside (i.e. I can use an FTP client on another machine on the LAN and connect to my cable modem's external IP address, which connects me to the FTP server; I assume the cable modem is looping back).

However, I can't seem to get Active Mode to work from the outside (or looping back through the cable modem/router). Active Mode works fine if I access the server directly across the LAN via its local static IP address, but not if I go through the router (via my external IP).  If I go through the router, either from inside or outside, I get a connection to the FTP server, but then when the FTP client executes a LIST command, it fails.

I've tried all sorts of port forwarding schemes within the Linksys router without success. Incidentally, previously I was running WFTPD as the FTP server and had the same problem.

(Also incidentally, if I turn on the Passive Mode option in GuildFTPd and configure the router with a trigger port of 21 and port range forwarding for the appropriate range, I can no longer make Passive Mode connections either!)

Is there any way to set up the Linksys BEFSX41 router to allow Active Mode FTP behind it?
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Question by:alisonnic
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6 Comments
 
LVL 31

Accepted Solution

by:
qwaletee earned 252 total points
ID: 9882473
See hre for explanation of active/passive:

http://slacksite.com/other/ftp.html
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LVL 35

Assisted Solution

by:ShineOn
ShineOn earned 248 total points
ID: 9886868
Active mode FTP (also known as PORT mode) uses both port 20 and 21.  Both must be available, so you need to port-translate port 20 to your Win98 box, too.

It still might not work, because many FTP clients expect to see the IP address of the server returned in a response, when doing active FTP, and if your FTP server sends your private IP address, that won't match up, and the active-mode connection will fail.
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Author Comment

by:alisonnic
ID: 12474857
Apologies for not responding to this sooner, and thanks to TheLearnedOne and modulo for cleaning this up.

Also, thanks to qualetee and ShineOn for the information about Active FTP.  I wasn't able to get it to work in my situation, and I suspect that the problem was that the server was returning its local IP address, as ShineOn suggested.
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