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An FTP servlet is an intermediate application that resides between the FTP server and the FTP client. It works as a proxy interposed within client/server communications and helps to unload some of the computing power of the FTP server and distribute it to the FTP servlet. It also provides a firewall and proxy friendly file transfer environment by wrapping FTP traffic over HTTP. FTP traffic can be wrapped over HTTPs using a SSL certificate to provide enhanced security.
FTP clients can connect to the FTP servlet through the Internet. In most cases FTP is wrapped over an application layer protocol. Most commonly used are HTTP (for easy, unencrypted transfers) or HTTPs (for encrypted transfers). The use of HTTPs requires an SSL certificate to be present at the site of the FTP servlet. A number of simultaneous connections can be made to the FTP servlet. The number of connections is restricted to the computing power of the server. The number of end-users supported through the number of connections is usually more. As all connected end-users aren’t “active” until they make a request from the server. Consequently, the number of end-users simultaneously online on the FTP server can be greater than the number of active connections supported by the FTP server.
FTP servlets protect direct access to an FTP server from the outside world. The FTP servlet can be housed on the DMZ. The internal network can house the FTP server. Direct access from the outside can’t be initiated with the internal FTP server. For additional security, port forwarding can also be used to enhance security between the DMZ and internal network.
Issues and drawbacks
FTP servlets can only work with advanced FTP clients that support the wrapping of FTP over HTTP or HTTPs. There are a number of commercially available clients/FTP servlets that work in such a way. Refer to Related links below.
- FTPS (FTP/SSL), FTP run over SSL
- Secure Copy (SCP), a protocol running over SSH
- Simple File Transfer Protocol (SFTP), the historic protocol RFC 913
- SSH file transfer protocol (SFTP, SH-FTP, FTP/SSH), a protocol running over SSH
- Trivial File Transfer Protocol (TFTP)
- Filecatalyst accelerated file transfer