jerome651 opened a new issue, #34:

   When configuring the "local-port" element within the /res/conf/ftpd-*.xml 
file to a static value, then the ability to run parallel active FTP transfers 
is lost, and results in an immediate "425" error for the other concurrent 
transfer attempts.
   When "local-port" is not configured, then the active mode data-port 
connections default to sourcing from "any available port" on the ftp server. 
For example, by default, a Windows 2016 server may choose a dynamic source 
data-port of 61753, when connecting back to the client at the location already 
specified by the client's PORT command. 
   Screenshot of test configuration:
   <img width="640" alt="apache-ftpserver 1 1 1 configuration using static 
source port" 
   When using another FTP server such as vsftpd, we can run parallel active 
transfers, all sourcing from a FTP server data-port of 20. 
   In that case, we would configure the option "connect_from_port_20=YES" in 
vsftpd's config file (RE:, so the 
FTP server isn't choosing dynamic source ports when connecting back to the 
client PORT location.
   I've tested this behavior with apache ftpserver v1.1.1, 1.1.4, and 1.2, and 
the behavior seems consistent among all of them.
   In this screenshot, my "ftp-dev-01" server has an IP of 
   When running a "10x parallel download" jmeter test, and running wireshark to 
inspect the responses, I see that the server only sends one SYN attempt from 
port 20 back to my client. I expect to see 10x SYN attempts. The one transfer 
succeeds, however the other 9 immediately return a "425" error:
   ![JMeter of 10x parallel active FTP DL's and wireshark showing only 1 SYN to 
   Attaching my jmeter 5.6.3 test, which uses 10 parallel threads to download a 
test.txt file from the server.
   [ftp server concurrent download JMETER 

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