A.yum install vsftpdB.yum remove vsftpdC.yum info vsftpdD.yum list vsftpd
A.ping 0.0.0.0B.ping 192.168.1.1C.ping 127.0.0.1D.ping 10.0.0.1
A.systemctl restart networkB.systemctl stop networkC.systemctl start networkD.systemctl enable network