This looks like some old bad advice from the internet. I've never found any of those items to stop a DDOS attack.
Someone may face with the DDOS attack. Let me talk about How to do When the server is under DDOS attack
1.Ensure that all servers use the latest systems , and security patches .
2.Ensure that administrators check on all hosts , not just for key host.
3.Make sure to remove unused services from the appropriate directory server or file database , such as FTP or NFS.
4.To ensure that all services running on Unix has TCP wrappers to limit access to the host。
5.Disable internal network through Modem connecting to the PSTN system.
6.Limit file sharing and network outside the firewall.
7.Ensure that there is a new network topology On your hand.
8. Check all logs network equipment and host / server system. As long as a loophole or a time log to change appears almost certain : the associated host security threat has been .