Are you setting up a SFTP (File transfer over SSH) or a FTPS (FTP over SSL) server?
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SFTP - Can't open data connection
Hi
I'm setting up secured by ssl ftp connection on my Filezilla FTP server. As long as i'm using standard TCP port for ftp connections (20 and 21) everything is working fine and I can connect from remote hosts without any problems. When i set up SFTP on TCP 990 remote hosts are able to connect but downloading directory structure fails as long as i'm connecting from host behind NAT. Hosts with external IP address connects just fine same like host within ftp server local network. I need to add that hosts with SFTP connection problems can connect on regular 21 port to same server without any problems.
FTP server config :
- System : Windows Server 2003 x64
- Software : Filezilla FTP Server
- Router : Cisco ASA 5510
- TCP ports forwarded : 20,21,990
Any tips will be appreciated ...
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Answers
Not an expert on FTPS, but the normal HTTPS / openssl tests appear to be valid, per: http://www.g6ftpserver.com
So I'd from both inside and outside you firewall (Private / Public IP) that you can establish an SSL connection e.g.
openssl s_client -connect ftp.mysite.com:990 -state -debug
Finally is working fine.
What has been done :
1. On server side - firewall :
- forwarded TCP 990 port on Cisco firewall to internal ftp server IP
- forwarded TCP 60000-60005 port range on Cisco firewall to internal ftp server IP
2. On server side - Filezilla software :
- General settings / Passive mode settings - marked USE THE FOLLOWING IP : external IP, marked don't use external IP for local connections, Use custom port range : 60000-60005
- SSL/TLS Settings : marked Enable SSL/TLS support, Allow explicit SSL/TLS on normal connections
3. On Client side : nothing :)
Results :
For clients behind NAT :
-ftp passive : not working
-ftp active : working
-ftps passive : working
-ftps active : not working
As you know FTP uses two connections a command/control and a data. The command/control connection is encrypted and thus firewalls can't see the PORT/PASV command and so they can't dynamically create rules to allow the data connection to be established.
You have passive working, by defining a specific range of ports that the server uses for passive ftp and then coding rules that specific allow inbound connections to those ports.
If you want active to work, then you need to code a rule in the firewall that specifically allows the servers IP address to establish a connection with the source port being TCP 20 and the destination port being any TCP port that is higher than 1023.
The other thing that will help with FTPS is to make sure you server and all ftp clients support extended mode active and passive data transfers. When using extended mode the IP address is not passed on the PORT (EPRT) or PASV (EPSV) commands. The other side assumes that the IP address to use for the data connection is the same as the IP address used for the command/control connection.
Extended mode was created to help with the problem of doing NAT with encrypted tunnels.
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by: arober11Posted on 2009-10-01 at 07:07:48ID: 25468762
Are you setting up a SFTP (File transfer over SSH) or a FTPS (FTP over SSL) server?
If it's the latter I'm guessing you either need to open a second port (data as well as command) or force all connections to be passive (single port).
Here's some background here:
http://www.experts-exchang
http://en.wikipedia.org/wi