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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP General File Transfer Protocols (FTP and TFTP)                      9  File Transfer Protocol (FTP)                           9  FTP Concepts and General Operation

FTP Operational Model, Protocol Components and Key Terminology 1 2 3 FTP Data Connection Management, Normal (Active) and Passive Data Connections and Port Usage

Anonymous FTP

Perhaps surprisingly, however, many organizations did not see the need for this enhanced level of security. They in fact went in the opposite direction: using FTP without any authentication at all. This may seem surprising; why would anyone want to allow just anybody to access their FTP server? The answer is pretty simple, however: anyone who wants to use the server to provide information to the general public.

Today, most organizations use the World Wide Web to distribute documents, software and other files to customers and others who want to obtain them. But in the 1980s, before the Web became popular, FTP was the way that this was often done. For example, today, if you have a 3Com network interface card and want a driver for it, you would go to the Web server www.3com.com, but several years ago, you might have accessed the 3Com FTP server (ftp.3com.com) to download a driver for it.

Clearly, requiring every customer to have a user name and password on such a server would be ridiculous. For this reason, RFC 1635 in 1994 defined a use for the protocol called anonymous FTP. In this technique, a client connects to a server and provides a default user name to log in as a guest. Usually the names “anonymous” or “ftp” are supported. Seeing this name, the server responds back with a special message, saying something like “Guest login ok, send your complete e-mail address as password.”. The password in this case isn't really a password, of course, it is just used to allow the server to log who is accessing it.

The guest is then able to access the site, though the server will usually severely restrict the access rights of guests on the system. Many FTP servers support both identified and anonymous access, with authorized users having more permissions (such as being able to traverse the full directory path, and having the right to delete or rename files) while anonymous ones may only be able to read files from a particular directory set up for public access.

FTP Operational Model, Protocol Components and Key Terminology 1 2 3 FTP Data Connection Management, Normal (Active) and Passive Data Connections and Port Usage