Virtual appliance FTP Proxy Server

Virtual appliance FTP Proxy Server

In fact FTP clients able to connect to FTP servers directly & can transmit & receive files or data directly through direct sockets connections, but in some situations security to FTP clients is required & maximum of the Internet users access the Internet from LAN network that is linked to the Internet through Firewalls that support NAT (Network Address Translation) or full LAN isolation via proxy server.

While FTP client joins to the FTP servers, it just resolves the FTP server address & joins to port 21 (default FTP port) & the FTP server responses with a welcome message, telling the FTP user that it is prepared to receive client authentication information. There are numerous ways the FTP client can tell the proxy server the address of the FTP server that it wants to connect. You can see from the mentioned figure that is taken from firewall setting of the “CuteFTP” client.

You need to take one alone:

1. General: You will not use the proxy & connect directly.

2. SITE site: For example you can see, the client sends authentication information first to the proxy which keeps it tell, it receives the FTP server title at “the SITE command” (e.g. site ftp.cuteftp.com), then the proxy joins the FTP server & resends the login information to the FTP server.

“lient: // connect to proxy server

proxy:  220 FTP Virtual Server

client: USER

proxy:  331 send password.

client: PASS

proxy:  230 Login OK. Proceed.

client: site ftp.cuteftp.com

proxy:  // connect to ftp.cuteftp.com

server: 220 GlobalSCAPE Secure FTP Server (v. 2.0)

proxy:  USER anonymous

server: 331 Password required for anonymous.

proxy:  PASS ********

server: 230 Login OK. Proceed.”

3. USER user@site: Here you can see, the client sends username & FTP server at “the USER command” (e.g. USER [email protected]), then the proxy connects the FTP server & sends the user name to the FTP server & dialog continues among the client & the server.

“client: // connect to proxy server

proxy:  220 FTP Virtual Server

client: USER [email protected]

proxy:  // connect to ftp.cuteftp.com

server: 220 GlobalSCAPE Secure FTP Server (v. 2.0)

proxy:  USER anonymous

server: 331 Password required for anonymous.

client: PASS ********

server: 230 Login OK. Proceed.”

Also you need to know about “USER with login”, “USER/PASS/ACCT”, “OPEN site” and you need to check each case with your FTP user alone because your FTP clients has different setting as well need to look the code that handles all of these cases. For code and more information this site is very useful for you.