answersLogoWhite

0


Best Answer

FTP is a TCP based service exclusively. There is no UDP component to FTP. FTP is an unusual service in that it utilizes two ports, a 'data' port and a 'command' port (also known as the control port). Traditionally these are port 21 for the command port and port 20 for the data port. The confusion begins however, when we find that depending on the mode, the data port is not always on port 20.

In active mode FTP the client connects from a random unprivileged port (N > 1023) to the FTP server's command port, port 21. Then, the client starts listening to port N+1 and sends the FTP command PORT N+1 to the FTP server. The server will then connect back to the client's specified data port from its local data port, which is port 20. From the server-side firewall's standpoint, to support active mode FTP the following communication channels need to be opened: * FTP server's port 21 from anywhere (Client initiates connection) * FTP server's port 21 to ports > 1023 (Server responds to client's control port) * FTP server's port 20 to ports > 1023 (Server initiates data connection to client's data port) * FTP server's port 20 from ports > 1023 (Client sends ACKs to server's data port)

In order to resolve the issue of the server initiating the connection to the client a different method for FTP connections was developed. This was known as passive mode, or PASV, after the command used by the client to tell the server it is in passive mode. In passive mode FTP the client initiates both connections to the server, solving the problem of firewalls filtering the incoming data port connection to the client from the server. When opening an FTP connection, the client opens two random unprivileged ports locally (N > 1023 and N+1). The first port contacts the server on port 21, but instead of then issuing a PORT command and allowing the server to connect back to its data port, the client will issue the PASV command. The result of this is that the server then opens a random unprivileged port (P > 1023) and sends the PORT P command back to the client. The client then initiates the connection from port N+1 to port P on the server to transfer data. From the server-side firewall's standpoint, to support passive mode FTP the following communication channels need to be opened: * FTP server's port 21 from anywhere (Client initiates connection) * FTP server's port 21 to ports > 1023 (Server responds to client's control port) * FTP server's ports > 1023 from anywhere (Client initiates data connection to random port specified by server) * FTP server's ports > 1023 to remote ports > 1023 (Server sends ACKs (and data) to client's data port)

User Avatar

Wiki User

โˆ™ 2009-06-03 23:31:12
This answer is:
User Avatar
Study guides

What are advantages of Database Approach

What is a network that covers a large geographical area such as a city country or world

What is the worlds largest wan

What is a network server

โžก๏ธ
See all cards
4.14
โ˜†โ˜…โ˜†โ˜…โ˜†โ˜…โ˜†โ˜…โ˜†โ˜…
156 Reviews

Add your answer:

Earn +20 pts
Q: What ports need to be open for the client to use the FTP client software?
Write your answer...
Submit
Still have questions?
magnify glass
imp
Related questions

Software searches a node for open ports?

Port scanner.


What is the name of the software that searches a node for open ports?

Port scanner


What ports do the game Eve Online use?

It appears that ports 3724 and 26000 need to be open for the game to function properly.


Which ports needs to be open in order for a user to access the internet?

I believe that the concept of "open ports" applies on the server side; meaning that the server will respond on certain ports. So basically, you need none on the side of the end-user.


What is the diffence between penetration testing and vulnerability scanning?

penetration is trying to get into a lan or client (ie. threw a open port) vulnerability is trying to find out if there is anything you can get into (trying to find if there are any open ports)


Why did china decide to open its ports located on the pacific ocean?

because the Americans need to be polluted


Do you have to pay to use Minecraft servers?

No, you do not. You can host a Minecraft server as long as you have connection. Please note that you need to open your ports on your router to make a Minecraft server. If you do not have access to this, you can download a VPN-software like Hamachi or Cisco.


Which websites allow one to download open source web design software?

One site that has open source web design software is Microsoft. You can use their notepad client to design webpages. Adobe also offers free trials on their world famous Adobe Dreamweaver software.


What is handshake in packet transmission?

The TCP 3 way handshake is when the server states what ports it has open, the client requests access to the port, and the server grants access. Layman's terms: Server - I have beer at my place. Client - Can I come over? Server - Sure!


What does the software program Active Ports allow computer users to do?

The program Active Ports allows one to enable all open TCP/IP and UDP ports on a local computer. The program has a rating of 3 stars out of 5 and has an average rating compared to other programs.


How do you open your ports?

Open the ports in a computer depends on the platforms and operating system being used . Open the Windows Firewall by clicking the Start button and clicking on the Control Panel. On the left pane, there is the Advanced settings which will open the ports.


What does TIFF Viewer software do?

The TIFF Viewer allows the user to open TIFF/TIF files. Depending on the software client, you may be able to convert to a PDF format which can be used with Adobe Reader.

People also asked