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FTP (File Transfer Protocol) is a protocol used to transfer and
manipulate files over a network that supports TCP/IP such as the internet, the
transferring operation needs two computers one is called the server and the
other one is the client (in web hosting the server is your web host and the
client is you). On each computer there is FTP software (on the server and the
client) the server waits for requests from the client side to make a connection
between them.
Port 21 over TCP is used to establish a control channel connection; this
connection is only used to exchange information between the server and the
client. To transfer data, another connection is established, if it's an active
connection, the server binds on port 20 before connecting to the client, but if
it's passive connection there is no need for binding.
Data is sent using two modes binary or ASCII
Anonymous FTP
Anonymous FTP allows anyone to access a remote server and download files
from there without asking for authentication, sometimes when username is
required you just need to enter "anonymous" and password would be your email
address if asked.
Security problem
Anyone can intercept your files and password and read them when using the
FTP, because FTP does not encrypt files when transferring them. To make things
safer and encrypted a secure kind of FTP was developed.
SFTP (SSH File Transfer Protocol) also called SecureFTP and FTPS which is
FTP run over SSL. These two kinds work in different manners but they both
encrypt data before transferring it.
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