FTP Client & Server woes

I am using a Netopia 3347 DSL Switch to connect to the internet. Behind that I have a Linsys VPN Firewall router.

Internet - Netopia - DMZ - Linksys - LAN

I have an exchange server and FTP server in the DMZ

Currently my workstations on the LAN can access most all web objects just fine. However, they can not access FTP.  Not the FTP server in the DMZ or any on the web.

Let's start with clients inability to access any ftp site first.




Netopia DSL Switch


Netopia ipmaps .105 to .198  and .108 to .111

Exchange server  and (dual nics)
FTP Server


LAN - 192.168.101.

LAN workstations can see second NIC on exchange server.  Email sends & recieves just fine.

Lan workstations (typ. Win 7 64) can not connect to FTP sites.

My particular workstation has ports 20,21,990 open in firewall (TCP)  and I can not connect to ftp://ftpmdot.state.mi.us/ (as an example) with either firefox or blaze ftp.
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hgj1357Connect With a Mentor Author Commented:
I fixed the problem by using https on port 443
Here are a few things to look at.

Go to a command prompt and try to telnet to port 21 on that site
e.g. "telnet ftpmdot.state.mi.us 21"
and see if it connects. If it does connect, then ftp is not blocked at the firewall and the router and you need to check the local PC. . If you cannot get out on the port, then check the log on the firewall and see if it is dropping or forwarding the packets. If it is not forwarding then it sounds like a firewall rule issue. Check the firewall and NAT rules. If you do not see the packets hitting the firewall then make sure you do not have a local firewall running on the PC that could be blocking you and causing the issue.

Good luck,
hgj1357Author Commented:
...Could not open a connection with the host, on port 21: Connect failed

Neither harware units have detailed logs of firewall activity.

How should the two be set up?  Should I pinhole 20,21 etc or should I not need to do that?
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Can you FTP from your exchange server to your FTP server?  Since they are both on the DMZ
hgj1357Author Commented:
Yes.  Mail server can FTP to FTP server.
hgj1357Author Commented:
SHould I pinhole ports 20,21,990 across the netopia?  If so, what private side IP should I use?  The private side of the netopia? The wan ip of the linksys?
Try to FTP outside from the DMZ.

I would take one of the workstations, give it an 192.168.10.x and throw it in the DMZ, verify that it can FTP to both the internet and the FTP server while on the DMZ.  If it can, than it is the Linksys that is blocking.
Dave BaldwinFixer of ProblemsCommented:
The FTP protocol uses many ports besides 20 and 21.  When I use Firefox to connect to that page, the data is returned at port 30463.  These are called 'ephemeral ports'.  Here's an article about them:  http://en.wikipedia.org/wiki/Ephemeral_port  I can't find one that strictly applies to FTP.
hgj1357Author Commented:
From a remote PC (home) I can ping the FTP server. When I try to connect, I get close. I get prompted for username / password - which is good, but it fails on authentication.
hgj1357Author Commented:
..although I can telnet in.  So, I need to figure out the security on the cerebus server, but that's not the issue here. At least right now.
From a remote PC (home) I can ping the FTP server. When I try to connect, I get close. I get prompted for username / password - which is good, but it fails on authentication.

This means you connected on port 21 but failed to open a data channel.  The data channel port is negotiated on the fly at runtime.  If you were using the DOS ftp.exe client then it was attempting to use an Active Mode data channel.  In active mode, the client machine sends its IP address to the server along with the port number where it will be waiting for the server to connect.  The port number is above 1024 and below 65K.  This often fails for two reasons: (1) the client sends a private IP address that the server can't reach like 192.168.x.x or 10.x.x.x and (2) many firewalls are configured by default to disallow inbound connections from some random machine out on the internet.  

Many firewalls can be configured to snoop the FTP control channel and watch for the command that asks for an Active Mode data channel.  When this happens, the firewall replaces the internal private address with a public address and then forwards the FTP server's inbound connection request to the correct client computer on the fly.  Once upon a time this was a high-end feature but now it is in consumer-level cable modems.
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