Q: What is FTP?
A: FTP stands for File Transfer Protocol. It's a way of transferring files over the internet.
Q: How does FTP work?
A: Similar to the web, FTP software is used to connect to a server; the server's address is entered into FTP client software, just as a web address is entered into a web browser. Available files and directories are shown in a list, and transfers can be made.
Q: What is FTP for?
A: FTP is good for quickly getting files - there's no fancy website to download and navigate, just a browsable directory structure. It's mainly used to host large libraries of files. Due to its simplicity, FTP support can be built into programs, and they can use it with no human interaction to obtain software updates and perform other automated data transfers. In addition, FTP has been around so long, it is a very robust protocol, and is very tolerant of slow or poor-quality connections.
Q: How fast is FTP?
A: That depends. Uploads are usually limited by your uplink speed. Downloads are affected by many things, including the load on the remote server, and other network traffic on the wire. FTP servers are usually resource-starved, overworked and somewhat neglected, and thus download speeds are not usually as fast as your downlink will permit.
Q: What software do I need to use FTP?
A: You need an FTP client. Your web browser probably supports FTP - but only in "passive" mode, and only for downloading. For uploading, and to use advanced features, you need special software such as WS_FTP, CuteFTP or Total Commander. Web browsers are notoriously unreliable FTP clients.
Q: Are there limits to the size of a file, number of concurrent connections, etc?
A: That depends on the server. FTP itself has no such limitations, however some FTP servers impose restrictions nonetheless. This is to conserve resources for other users.
Q: I want to send a file to my colleague across the office. Can I use FTP to send it to him?
A: Not really - it's possible, but it would be easier to copy the file to a shared directory on your local fileserver, or email it. FTP is more used to access large, central file repositories, rather than for ad-hoc peer-to-peer transfers. In particular, your colleague would need to set up an FTP server just so you could upload the file to him.
Q: I get timeouts and can never connect. What's wrong?
A: Try accessing the site in 'passive mode'. And/or, check your firewall is permitting TCP traffic on port 21.
Q: How do I use FTPS?
A: See this page: How to use FTPS (FTP-over-SSL/TLS)
Q: If I upload a lot of files on a fast connection, my transfer freezes mid-way through. I cannot then reconnect. What's wrong?
A: Your router may be interpreting the FTP traffic as a Denial-Of-Service attack, and blocking the connection. You can verify this by inspecting your firewall logs. Try one of the following:
- use passive mode
- use FTPS (this is the recommended option, but your FTP client must support it)
- use a rate-limiter/throttle (this normally needs to be built into your FTP client)
Note: although disabling your firewall or your intrusion detection will probably work, this isn't really a fix because you'll be a lot less secure than previously. Do not do this. We recommend using FTPS, as it provides more security than plain old FTP, as well as fixing the "frozen connection" problem noted.
Q: What about viruses?
A: Viruses are a danger. You should ensure that anti-virus software is installed on your machine. Even with anti-virus software installed, you should still exercise caution when executing software downloaded from FTP servers.