Passive ftp how does it work

When configuring passive FTP, there is typically a field in your server side configuration that effectively tells the client "Use this IP address to connect for the data session. When placed behind a stateful firewall like an MX Security Appliance, this will often be a private LAN address, and result in the client session attempting to connect to a nonexistent IP range to retrieve data. When placed behind a firewall, this field must be changed to be the public IP that ports are being forwarded from, or the public IP in use for a NAT address on the firewall.

Note: Microsoft IIS version 6 and earlier do not have a configurable option for server IP, which may cause issues when configuring passive FTP behind any stateful firewall. This article provided an overview of the mechanisms used by active and passive FTP.

For a more detailed discussion of passive and active FTP, please consult this documentation. The server responds with an ACK. The client sends an ACK to the server. The FTP session has now been established. A firewall acts as a security measure to prevent unauthorized access to a computer network.

To access the Internet applications may require special configuration options. If a firewall is preventing the connection, the most common error message is the "Cannot make connection to host" error message. Firewalls typically allow passive FTP connections without requiring additional configuration information. Passive FTP can slow down the connection process. Legal Notices Online Privacy Policy. That's not true. Each file transmitted during that entire login session will actually require at least one port.

So if 10 files are downloaded, then 10 ports are used. That's not all. Some clients now use multiple connections when uploading files. For example, if a client has files to upload, it might spawn 5 separate sessions to make the upload go faster. The result is that a single client may have 5 open passive connections at a time. So, when deciding how many passive ports you want to open you need to consider that a single client may actually open multiple concurrent passive connections.

While there are no hard and fast rules dictating the number of ports that should comprise a port range, you will really want to project your maximum number of concurrent users and allocate a sizable allowance based on that. In the event that the IP address your server uses in responding to requests for passive connections is not routable via the Internet, you'll need to enter your public IP address in the Passive IP field. We hope we were able to explain the difference between active and passive FTP in a manner you could easily understand.

Would you like to try this yourself? Active vs. Get Your Free Trial Would you like to try this yourself? Related Posts Active-Active vs.

Although Active mode is the most used and default mode, Passive mode is helpful in certain situations where you are port limited. Active vs. Why does this difference matter? Start Your Free Trial! Learn More.