VSFTPD - limit the number of simultaneous connections for a single IP address

By default VSFTPD allows unlimited connection from the same client IP address.

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

2: Setup limitation

Set up the max_per_ip=4 (this will limit simultaneous connection to 4 number only)
max_per_ip=4

3: Restart vsftpd

# /etc/init.d/vsftpd restart