Wat is FTP

1. Wat is FTP

File transfer protocol (FTP) is a network protocol that allows data from one node to send to another network via a (bv. the Internet, the home network). With an FTP server, it is very easy to send files to our hosting providers or rather upload and / or downloaden.FTP is a special service because it uses two ports during a session, a “data” and a gate “command” (also known as the”control” ) port. Traditionally these are port 21 for the command port and 20 for the data port. However, the confusion begins to, Depending on the mode, The data port is not always port 20 is.

1.1 FTP types

The FTP protocol has two variants: Passive FTP and Active FTP The difference between the two lies in how a session is established for file. Both require a client / server connection, and both use the underlying Transfer Control Protocol ( TCP ) en het Internet Protocol ( IP ) for the routing , data flow control , error detection and error correction. However, active FTP uses 2 Ports , while passive FTP makes use of only one port .

1.2 Active FTP

With active FTP, the FTP server makes a new connection back to the client to transfer the requested data, when a user connects to a remote FTP server and requests information or a file. This is called the data connection called. To start the FTP client chooses a random (random) port to the “data connection” receive. The client sends the port number it chose to the FTP server and then listens for an incoming connection on that port. The FTP server then initiates a connection to the address of the client on the chosen port and transfers the data. This is a problem for users attempting to gain access to FTP servers from behind a NAT gateway. Because of how NAT works, the FTP server initiates the “data connection” by connecting to the external address of the NAT gateway on the chosen port. The NAT machine will receive this, but because he has no figure for the packet in its state table, he will drop the packet and will not deliver it to the client.

1.3 Passive FTP

In passive mode FTP, asks the client to the server pick a random port to listen on for the “data connection”. The server informs the client of the port it has chosen, and the client connects to this port to transfer the data. Unfortunately, this is not always possible or desirable due to the presence of the firewall prior to the FTP server that the incoming “data connection” block. The most common connection is done via the passive FTP, it is easier for the client to connect more difficult for the admin to manage, This will however need to do some work in the firewall.

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