How to Prevent DDoS Attacks: Protect Your Linux Server

How to Prevent DDoS Attacks: Protect Your Linux Server

DDoS attacks are a common network security threat that can make a server overloaded or unavailable. In this article, we will introduce several ways to protect your Linux server from DDoS attacks, including optimizing network configuration, using firewalls, and installing DDoS protection software.

1. Optimize network configuration
   Optimization of network configuration is the first step to ensure that your server can withstand large amounts of traffic. The following are several key configuration optimization suggestions:

   • Increase server bandwidth: Make sure your server bandwidth is sufficient to support high-load traffic.
   • Adjust TCP parameters: Adjust TCP parameters according to the performance and needs of the server, such as adjusting the TCP receive and send buffer sizes to improve network throughput and response speed.
   • Enable SYN Cookies: SYN Cookies are a method to prevent SYN Flood attacks. SYN Cookies are dynamically generated and verified during the TCP three-way handshake to prevent attackers from consuming server resources.

Here is an example of using the sysctl command to adjust TCP parameters:

# 打开TCP的SYN Cookie保护
sysctl -w net.ipv4.tcp_syncookies=1

# 增大TCP接收缓冲区大小
sysctl -w net.core.rmem_max=26214400

# 增大TCP发送缓冲区大小
sysctl -w net.core.wmem_max=26214400

2. Using a firewall
   A firewall can help you filter and restrict traffic to the server to prevent DDoS attacks. Here are some example rules for using iptables firewall to protect your server:

# 允许已建立的连接通过
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

# 允许SSH流量通过
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# 限制ICMP流量
iptables -A INPUT -p icmp --icmp-type echo-request -m limit --limit 1/s -j ACCEPT
iptables -A INPUT -p icmp -j DROP

# 限制特定的端口流量
iptables -A INPUT -p tcp --dport 80 -m limit --limit 100/minute -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

The above rule examples are just a starting point, you can adjust the firewall rules according to your needs and network environment.

3. Install DDoS protection software
   In addition to configuring the network and using a firewall, installing specialized DDoS protection software is also an important way to protect Linux servers from DDoS attacks. Here are some common software:

   • ModSecurity: An open source web application firewall that can detect and block malicious HTTP/HTTPS requests.
   • Fail2Ban: An automated tool that blocks malicious login attempts and malicious requests. It can be used to protect SSH, FTP and other services.
   • Nginx Anti-DDoS: An Nginx-based protection software that can resist DDoS attacks by limiting concurrent connections and request rates.

When installing these software, please follow the guidelines in the official documentation and configure them as needed.

To sum up, by optimizing network configuration, using firewalls and installing DDoS protection software, you can enhance the security of your Linux server and reduce the risk of DDoS attacks. Remember, network security is an evolving field, and timely updates and security measures are key to keeping your server secure.

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