DDOS attack is very harmful. It can cause the downtime of the target server, resulting in the inaccessibility of the website and the failure of normal business operations. In serious cases, it may even lead to data loss, financial loss and other problems. Since attackers can launch attacks by controlling a large number of computers and devices, it is difficult to determine the location and identity of the attack source, which increases the difficulty of defense.

In order to defend against DDOS attacks, various measures can be taken, such as using CDN to accelerate, setting up firewalls, using DDOS attack cleaning services, etc. These measures can effectively reduce the impact of attacks. At the same time, it is also necessary to strengthen server security measures to reduce the possibility of being attacked, such as strengthening password management, updating patches in a timely manner, and using security software.

The following are some effective measures to defend against DDOS attacks:

1. Cloud service providers with strong attack resistance capabilities: choose cloud service providers with strong attack resistance capabilities. They usually use a variety of defense technologies and devices to protect users' websites or applications.

2. Website CDN acceleration: Using the content distribution network (CDN) can distribute the content of the website to multiple nodes around the world, reducing the pressure on a single node and enhancing the ability to resist DDOS attacks.

3. Cleaning traffic: Use professional DDOS attack cleaning services to clear DDOS attack traffic, and only forward normal traffic to the target server.

4. Firewall: The firewall can detect and filter malicious traffic to prevent DDOS attacks.

5. Limit the number of connections: Set connection restrictions, such as IP restrictions, connection number restrictions, etc., to limit the number of connections of a single IP, which can effectively reduce the impact of DDOS attacks.

6. Load balancing: Using load balancing technology, traffic can be distributed to multiple servers to enhance the ability to resist DDOS attacks.

7. Data packet filtering: Use data packet filtering technology to filter out some obvious DDOS attack data packets and reduce the impact of the attack.

8. Reduce the attack surface: closing unnecessary services, ports and functions to reduce the attack surface can reduce the possibility of DDOS attacks.

9. Contingency plan preparation: formulate a contingency plan for defending against DDOS attacks, including backup data, disaster recovery plans, etc., to quickly restore the attacked system.

The above measures can be used in combination to improve the ability to resist DDOS attacks. Appropriate defense measures need to be selected according to the actual situation.