Active 11 months ago. Viewed k times. Active and passive are the two modes that FTP can run in. Once the client knows that, it can then successfully create the data channel and continue. I don't think the statement around the port Y is right, in active mode the client does not determine the port Y, the server tries to randomly choose a port and tries to see whether the client would allow the communication via that chosen port. The reason I say this is that, if this is not true my argument then the client side even if it is behind a firewall can always create two fire-wall rules one for the outgoing connection and one for the incoming connection.
Example: in corporate environments, there's typically a firewall between the company-wide network and the outside world, over which a client running FTP has zero power. IN Passive mode, why server sends client a random port to client instead client connects to server port 20 directly? Why can't client directly open up a data channel from client port no to port no 20 on server side?
I asked the question here now networkengineering.
Active mode: Passive mode: In an active mode configuration, the server will attempt to connect to a random client-side port. Yuantao Yuantao 2, 1 1 gold badge 12 12 silver badges 16 16 bronze badges.
What is the difference between Active and Passive FTP?
I am just guessing which is the security issue. If server listen to the same port 20 then it can not understand which client is talking, so it choose a random port and send it to the client, starting to listen to that port. When client connect to that port, server know which client it belongs to.
- mac mini 2008 max ram.
- How to use CyberDuck FTP client for Mac?.
- File Transfer Protocol - Wikipedia.
- 1. Select “Preferences” from the “Safari” menu of the browser toolbar..
- File Transfer Protocol.
But it is enough for a MITM to connect to the same client. Passive : FTP connection mode active or passive , determines how a data connection is established. Network Configuration for Passive Mode With the passive mode, most of the configuration burden is on the server side. Network Configuration for Active Mode With the active mode, most of the configuration burden is on the client side.
Martin Prikryl Martin Prikryl k 25 25 gold badges silver badges bronze badges.
Active mode: -server initiates the connection. Passive mode: -client initiates the connection. Saeed Aliakbari Saeed Aliakbari 1 1 silver badge 11 11 bronze badges. DaveW DaveW 1 3 3 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. While transferring data over the network, four data representations can be used:   .
For text files, different format control and record structure options are provided. These features were designed to facilitate files containing Telnet or ASA. Data transfer can be done in any of three modes:  . This mode was described in an Internet Draft , but not standardized. FTP login uses normal username and password scheme for granting access. Although users are commonly asked to send their email address instead of a password,  no verification is actually performed on the supplied data.
FTP normally transfers data by having the server connect back to the client, after the PORT command is sent by the client. This is problematic for both NATs and firewalls, which do not allow connections from the Internet towards internal hosts. There are two approaches to solve this problem. HTTP essentially fixes the bugs in FTP that made it inconvenient to use for many small ephemeral transfers as are typical in web pages.
nilveleslio.tk FTP has a stateful control connection which maintains a current working directory and other flags, and each transfer requires a secondary connection through which the data are transferred. In "passive" mode this secondary connection is from client to server, whereas in the default "active" mode this connection is from server to client.
This apparent role reversal when in active mode, and random port numbers for all transfers, is why firewalls and NAT gateways have such a hard time with FTP. HTTP is stateless and multiplexes control and data over a single connection from client to server on well-known port numbers, which trivially passes through NAT gateways and is simple for firewalls to manage.
Setting up an FTP control connection is quite slow due to the round-trip delays of sending all of the required commands and awaiting responses, so it is customary to bring up a control connection and hold it open for multiple file transfers rather than drop and re-establish the session afresh each time. In contrast, HTTP originally dropped the connection after each transfer because doing so was so cheap.
While HTTP has subsequently gained the ability to reuse the TCP connection for multiple transfers, the conceptual model is still of independent requests rather than a session. When FTP is transferring over the data connection, the control connection is idle. If the transfer takes too long, the firewall or NAT may decide that the control connection is dead and stop tracking it, effectively breaking the connection and confusing the download.
The single HTTP connection is only idle between requests and it is normal and expected for such connections to be dropped after a time-out. As of , major browsers such as Chrome and Firefox are deprecating FTP support to varying degrees,  with Google planning to remove it entirely by Chrome Mozilla is currently discussing proposals, including only removing support for old FTP implementations that are no longer in use to simplify their code.
More details on specifying a username and password may be found in the browsers' documentation e. By default, most web browsers use passive PASV mode, which more easily traverses end-user firewalls.
Mac OS X 10.6 and later
Some variation has existed in how different browsers treat path resolution in cases where there is a non-root home directory for a user. FTP was not designed to be a secure protocol, and has many security weaknesses. If you use a different FTP program, it almost certainly has a checkbox to turn on "passive mode" in either the connection setup screen or the program preferences screen. Consult the documentation for your FTP program if you're unsure how to do it.
The first thing we recommend is turning off any firewall software as a test. If this fixes the problem, consult your firewall's documentation or support to learn how to allow FTP connections with the firewall turned on. Encryption is not compatible with all firewalls. If that doesn't solve it, try connecting to a completely different public FTP server. This will show whether the problem is just with the connection to our FTP server or if your computer is having problems connecting to any FTP servers. An example of a public FTP server is:.
If your computer cannot connect to that server, then either your FTP software is not working correctly, or something on your computer probably a firewall or other security software is blocking all FTP connections. If you still having problems connecting, try making a text connection as described in the next section. These instructions explain how to make a text-based connection to our servers, mimicking what your FTP program usually does invisibly.