FTP servlet an intro

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.

Architecture

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.

Security

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.

File-sharing program

A file-sharing program is used to directly or indirectly transfer files from one computer to another computer over a network (e.g. the Internet). While the term may be used to describe client-server disk sharing (also known as shared file access or disk mounting), it is more commonly used to describe file sharing using the peer-to-peer (P2P) model.

Peer-to-peer file sharing typically operates using a network, such as Gnutella or BitTorrent. There are trade offs to using one network over another network. A variety of file-sharing programs are available on these different networks. It is common for commercial file sharing clients to contain abrasive advertising software or spyware.

Categories of clients

* Centralized Clients: OpenNap
o Benefits: Faster searching and downloading
o Negatives: Often more vulnerable to legal and DDOS attacks

* Decentralized clients: Gnutella
o Benefits: Usually more reliable and rarely shut down
o Negatives: Generally slower than centralized systems

* Decentralized tracker-based clients: BitTorrent
o Benefits: Very fast due to concentration of bittorrent networks on a single file, is principally used to offer new, large files for download, many tracker sites available
o Negatives: Not centrally searchable, tracker sites are often closed down from legal suits or fail, not truly anonymous

* Multi-network clients
o Benefits: allows connection to more than one network, almost always on the client side.
o Negatives: often playing catch-up to individual networks' changes and updates.

* Anonymous peer-to-peer: Freenet, GNUnet, MUTE, I2P
o Benefits: allows for the uncensored free flow of information and ideas
o Negatives: due to anonymity it allows for questionable or illegal material to be exchanged easier than other networks, often slower than regular p2p because of the overhead

* Private file-sharing networks

Economic impact

As files sharing has spread a debate on how the infringement of copyright (in terms of file sharing copyrighted audio and visual content) impacts on legal distribution of especially music. In a broader context commentators have pointed out that the music industry, along with other types of media such as film and TV are having a difficult time adapting to the digital age.

Software Industry

According to Moisés Naím, even in countries and regions with high intellectual property enforcement standards, such as the US or the EU, piracy rates of one-quarter or more for popular software and operating systems are common. The pirated software is distributed through file sharing at unprecedented rates, and according to Naím, software manufacturers dread the "one disc" effect: a phenomenon in which a single counterfeited copy can be propagated until it has taken over an entire country, pushing the legitimate product out of the market.

FTP over SSH

FTP over SSH refers to the practice of tunneling a normal FTP session over an SSH connection.

Because FTP uses multiple TCP connections (unusual for a TCP/IP protocol that is still in use), it is particularly difficult to tunnel over SSH. With many SSH clients, attempting to set up a tunnel for the control channel (the initial client-to-server connection on port 21) will protect only that channel; when data is transferred, the FTP software at either end will set up new TCP connections (data channels) which will bypass the SSH connection, and thus have no confidentiality, integrity protection, etc.

If the FTP client is configured to use passive mode and to connect to a SOCKS server interface that many SSH clients can present for tunneling, it is possible to run all the FTP channels over the SSH connection.

Otherwise, it is necessary for the SSH client software to have specific knowledge of the FTP protocol, and monitor and rewrite FTP control channel messages and autonomously open new forwardings for FTP data channels. Version 3 of SSH Communications Security's software suite, and the GPL licensed FONC are two software packages that support this mode.

FTP over SSH is sometimes referred to as secure FTP; this should not be confused with other methods of securing FTP, such as with SSL/TLS (FTPS). Other methods of transferring files using SSH that are not related to FTP include SFTP and SCP; in each of these, the entire conversation (credentials and data) is always protected by the SSH protocol.