Distributed denial of service (DDoS) attacks are a common type of cyber attack in which a large number of malicious traffic is directed at a server or network in an attempt to disrupt or shut down access to a website or online service. DDoS attacks can be difficult to defend against, but there are several steps you can take to protect your Linux server from these types of attacks.

Use a Firewall

One of the most effective ways to protect your Linux server from DDoS attacks is to use a firewall. A firewall is a security system that monitors and controls the incoming and outgoing network traffic based on predetermined security rules. There are many firewall solutions available for Linux, such as iptables and ufw.

To set up a firewall on your Linux server, you will need to install the firewall software and configure the security rules. This can typically be done using the command line. For example, to set up a basic firewall using iptables, you might use the following commands:

sudo apt-get install iptables
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT
sudo iptables -A INPUT -j DROP
sudo iptables-save
These commands will install iptables, allow incoming traffic on ports 80 and 443 (for HTTP and HTTPS), and drop all other incoming traffic. You can customize these rules to fit your specific needs.

Use a DDoS Protection Service

Another option to protect your Linux server from DDoS attacks is a DDoS protection service. These services use advanced techniques such as traffic scrubbing and rate limiting to mitigate DDoS attacks before they reach your server. Some popular DDoS protection services for Linux servers include Cloudflare and Incapsula.

To use a DDoS protection service, you will need to sign up for an account and configure your server to route traffic through the service. The specific steps will depend on the service you choose and your server setup, but generally, you will need to update your DNS records and configure your firewall to redirect traffic to the service.

Monitor Network Traffic

Monitoring your server’s network traffic can help you detect DDoS attacks and take appropriate action. There are several tools available for monitoring network traffic on Linux, such as netstat and tcpdump.

To use netstat, you can use the following command:

netstat -anp | grep -i "tcp"

This will display a list of all active TCP connections on your server, along with the associated process ID. You can use this information to identify unusual or excessive traffic and take appropriate action.

Tcpdump is another tool that allows you to capture and analyze network traffic. To use tcpdump, you can use the following command:

tcpdump -nn -i eth0

This will capture and display all network traffic on interface eth0. You can use the various options available with tcpdump to customize the capture and analysis.

Use Content Delivery Networks (CDNs)

Content delivery networks (CDNs) can help protect your Linux server from DDoS attacks by distributing your website’s content across a global network of servers. This makes it more difficult for attackers to target a single server and can help mitigate the impact of a DDoS attack