---
title: DDoS Attacks
description: "DDoS is a distributed attack type \"denial of service\". In this attack, the server receives many false requests. As a result, the server is overloaded and cannot serve real users."
---

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2. [Server Administration](https://help.ishosting.com/en/server-administration)
3. [DDoS Protection](https://help.ishosting.com/en/server-administration#ddos-protection)

# DDoS Attacks

## This article covers the causes and types of DDoS attacks, as well as key steps for detecting an attack, protecting your server, and minimizing the impact.

### General Information About DDoS

**DDoS** is a **distributed attack** type **"denial of service"**. In this attack, the server receives many false requests. As a result, the server is overloaded and cannot serve real users.

**DDoS attacks** are carried out from various remote hosts (computers and other network-connected devices). Typically, the users of these devices are unaware that their equipment is participating in an attack on another computer. Attackers infect numerous devices with malware in advance, turning them into "zombie computers." These devices do not immediately begin attacking servers; instead, the attacker sends a command at a specific time specifying which server to target.

The number of internet-connected devices has risen sharply in recent years. However, due to their low cost, many of these devices have significant security vulnerabilities. Examples include smart TVs, electric kettles, microwave ovens, children's toys, and other connected appliances.

A DDoS attack disrupts service for all users of the targeted virtual server. The internet connection becomes clogged with traffic originating from these zombie computers.

### Reasons for DDoS Attacks

1. **Unfair competition.** Attacks are frequently commissioned by rival companies. If an organization's website goes down for even a few hours, it can lead to significant financial losses and a loss of customers. Prolonged server downtime can have catastrophic consequences.
2. **Personal motives.** Attacks may also be organized or commissioned for personal reasons. Employees often launch attacks to retaliate against former employers.
3. **Extortion.** Attackers may launch an attack and then demand payment from the resource owner to stop it.
4. **Random hacking.** Some attackers target websites at random. They may do this for "practice" or simply for amusement.

### Types of DDoS Attacks

- **HTTP flood**: HTTP requests are sent to a domain. These requests are typically varied and generate the maximum possible load on the server (e.g., targeting PHP scripts or dynamic elements).
- **UDP flood**: UDP packets are sent to the server's IP address. This saturates the server's internet bandwidth. This type of attack generates a massive volume of inbound traffic. Consequently, other nodes sharing the same communication channel as the target server may also be affected.
- **TCP SYN flood**: An attack targeting the server's IP address. The server receives a large number of connection requests from non-existent addresses. The connection queue becomes overwhelmed, preventing legitimate connections from being established. Real users are unable to connect because the queue is clogged with bogus requests.

### DDoS Attack Categories

Depending on the target being disabled during a DDoS attack, attacks are classified into four categories operating at different layers of the OSI model.

| **ATTACK TYPE** | **ATTACK TARGET** |
| --- | --- |
| **First Grade (L2)** | - Bandwidth saturation - NTP amplification - DNS amplification - RIP amplification - ICMP flood - UDP flood - SYN flood - etc. |
| **Second Grade (L3)** | - Disruption of network infrastructure - Attacks causing BGP routing issues - Attacks causing network advertisement issues - Issues affecting transit network equipment - etc. |
| **Third Grade (L4)** | - Exploitation of TCP stack vulnerabilities - TCP connection flood - Slowloris - Slow POST - etc. |
| **Fourth Grade** **(L7)** | - Web application degradation - GET Flood - POST Flood - HTTP Flood - Repeated retrieval of specific information from the database, memory, or disk, resulting in server resource exhaustion, etc. |

### General Actions During a DDoS Attack

- **Confirm the attack**. Check traffic graphs, server load, connection counts, and logs to rule out a normal spike in activity.
- **Identify the type and source of the load**. Determine which IP addresses, ports, protocols, or URLs are generating anomalous traffic.
- **Contact your hosting provider**. Report the attack start time, server IP, observed symptoms, and any other available information.
- **Enable DDoS protection** if provided by your hosting provider or an external service.
- **Restrict unwanted traffic**. Use firewalls, ACLs, iptables/nftables, and other filtering tools.
- **Limit the number of connections and requests**. Configure rate limiting for the web server, API, and other public-facing services.
- **Close unused ports** **and services** to reduce the attack surface.
- **Use a CDN or reverse proxy for websites** to filter requests before they reach the server.
- **Avoid manually blocking large numbers of IPs** if the attack sources are constantly changing; this is ineffective and may block legitimate users.
- **Monitor server resources**. Track CPU, RAM, network usage, connection counts, and service availability during the attack.
- **Analyze logs and configurations after the attack**. Identify the primary target, adjust filtering rules, and prepare measures for potential future attacks.
- **Set up continuous monitoring** **and alerts** to respond faster.

### If the Server Has Become the Source of a DDoS Attack

If your server has become the source of a DDoS attack, it is recommended to take the following steps:

- Restore the server from the last known good backup.
- Change all server access passwords (SSH, SFTP).
- Update control panel plugins.
- Run an [antivirus scan](https://help.ishosting.com/en/antivirus) on the server.

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