What Is a DDoS Attack and How to Defend Against It Print

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What Is a DDoS Attack and How to Defend Against It

A DDoS (Distributed Denial of Service) attack is an advanced form of DoS attack designed to make a website or online service inaccessible to legitimate users.

Unlike a traditional DoS, a DDoS attack is launched from a distributed network of compromised devices (a botnet), often infected with malware or trojans and controlled remotely.

The target server is overwhelmed by a massive volume of simultaneous requests, exceeding its processing capacity and causing service disruption.

 

Phases of a DDoS Attack

  • Intrusion Phase: the attacker compromises multiple vulnerable systems and infects them with remote control tools.
  • Distributed Attack Phase: once the botnet is assembled, the attacker directs the traffic flood to the victim’s server, causing overload and failure.

 

How to Detect a DDoS Attack

1. Monitor server load

On Linux systems, check the server load using:

# w
# uptime

Example output:

12:00:36 up 1 day, 20:27, 5 users, load average: 0.70, 0.70, 0.57

If the average load exceeds 5, further investigation is advised.

2. Check active HTTP processes

# ps -aux | grep HTTP | wc -l

More than 100 active HTTP connections may indicate an ongoing DDoS attack.

3. Identify suspicious IPs

# netstat -lpn | grep :80 | awk '{print $5}' | sort

If you see over 30 connections from the same IP or multiple IPs from the same network, it could be a sign of attack.

 

How to Mitigate a DDoS Attack

Block Suspicious IPs with CSF

If you are using ConfigServer Security & Firewall (CSF), block suspicious IPs using:

# csf -d 127.0.0.0
# csf -d 111.0.0.0/8
# csf -d 111.111.0.0/16
# csf -d 111.111.111.0/24

Use Advanced Protection Like Cloudflare

Cloudflare is a highly effective global security platform that helps mitigate even large-scale and complex DDoS attacks.

 

💡 Technical Tip

Every DDoS case is unique. If you suspect an attack, contact our technical support immediately for analysis and a custom mitigation strategy.

 


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