The problem of the loss of the network port of the plug-in network cable and the slow upload and download transmission of vsftpd

Reason description, in centos, the IP of the network port is lost after plugging and unplugging the network port.
The solution is:
# chkconfig NetworkManager off Permanently closed, network management status

# systemctl disable NetworkManager Permanently close the network management command

Restart method when bug appears: systemctl reboot -ff

Set the kernel boot sequence: grub2-set-default 0

Linux questions and answers: How to install Shrew Soft IPsec VPN on Linux
Link: https://www.jqhtml.com/34961.html

Reasons for slow ssh connection waiting time
vi /etc/ssh/sshd_config

#UseDNS yes

Change to UseDNS no

Restart ssh to solve

service sshd restart

The configuration method of vsftpd slow local download:

Configure the following information under
/etc/vsftpd/vsftpd.conf : reverse_lookup_enable=NO
#After configuring the local vsftpd service, configure the user name and account

Restart vsftpd