Q. How do I force VSFTPD ftp server to limit the number of simultaneous vsftpd connections from the same IP address under Debian Linux?

A. By default VSFTPD allows unlimited connection from the same client IP address. You can easily force vsftpd ftp server to use limited number of connection. There is a special directive called max_per_ip.

Step # 1: Open vsftpd.conf file

Use text editor such as vi to edit /etc/vsftpd.conf or /etc/vsftpd/vsftpd.conf file:
# vi vsftpd.conf

Step # 2: Setup limitation

Set up the max_per_ip=3 (this will limit simultaneous connection to 3 number only)
max_per_ip=3

You are restricting end user to a specific host to 3 concurrent connections.

Step # 3: Restart vsftpd

# /etc/init.d/vsftpd restart

Now vsftpd should limit the number of simultaneous vsftpd connections for a single IP address. If end user try to cross this limit she will see following error message:

421 There are too many connections from IP address.