How to enable DDoS protection?

Question

DDoS (Distributed Denial of Service Attacks) are generally blocked on a server level right?

Is there a way to block it on a PHP level, or at least reduce it?

Answer 1

According the PHP part of the question;

Although I don't rely on PHP for this, it could be implemented but needs to consider all these possiblities or more;

1. Attacker may change IP for each request
2. Attacker may pass parameter(s) to URI that target site doesn't care these parameter(s)
3. Attacker may restart the session before expiry ...

Simple pseudo;