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The differences between DoS and DDoS are substantive and worth noting. In a DoS attack, a perpetrator uses a single Internet connection to either exploit a software vulnerability or flood a target with fake requests—usually in an attempt to exhaust server resources (e.g., RAM and CPU).

On the other hand, distributed denial of service (DDoS ) attacks are launched from multiple connected devices that are distributed across the Internet. These multi-person, multi-device barrages are generally harder to deflect, mostly due to the sheer volume of devices involved. Unlike single-source DoS attacks, DDoS assaults tend to target the network infrastructure in an attempt to saturate it with huge volumes of traffic.

DDoS attacks also differ in the manner of their execution. DoS attacks are typically launched using homebrewed scripts or DoS tools (e.g., Low Orbit Ion Canon) while DDoS attacks are launched from botnets—large clusters of hacker-controlled connected devices (e.g., cellphones, PCs or routers).

Denial of Service Attack Types

DoS attacks can be divided into two general categories:

1. Application layer attacks (a.k.a., layer 7 attacks) can be either DoS or DDoS threats that seek to overload a server by sending a large number of requests requiring resource-intensive handling and processing. Among other attack vectors, this category includes HTTP floods, slow attacks (e.g., Slowloris or RUDY) and DNS query flood attacks.

UDP/DNS flood - 25 million packets per secondThe size of application layer attacks is typically measured in requests per second (RPS), with no more than 50 to 100 RPS being required to cripple most mid-sized websites.

2. Network layer attacks (a.k.a., layer 3–4 attacks) are almost always DDoS assaults set up to clog the “pipelines” connecting your network. Attack vectors in this category include UDP flood, SYN flood, NTP amplification and DNS amplification attacks, and more.

Any of these can be used to prevent access to your servers, while also causing severe operational damages, such as account suspension and massive overage charges.

DDoS attacks are almost always high-traffic events, commonly measured in gigabits per second (Gbps) or packets per second (PPS). The largest network layer assaults can exceed 200 Gbps; however, 20 to 40 Gbps are enough to completely shut down most network infrastructures.

Preparing for DoS Attacks

You can’t prevent DoS assaults. The fact is that cybercriminals are going to attack. Some are going to hit their targets, regardless of the defenses in place.

However, there are steps you can take to spot a brewing storm, including:

  • Monitoring your traffic to look for abnormalities, including unexplained traffic spikes and visits from suspect IP address and geolocations. All of these could be signs of attackers performing “dry runs” to test your defenses before committing to a full-fledged attack. Recognizing these for what they are can help you prepare for the onslaught to follow.
  • Keep an eye on social media (particularly Twitter) and public wastebins (e.g., for threats, conversations and boasts that may hint on an incoming attack.
  • Consider using third-party DDoS testing (i.e., pen testing) to simulate an attack against your IT infrastructure so you can be prepared when the moment of truth arrives. When you undertake this, test against a wide variety of attacks, not just those with which you are familiar.
  • Create a response plan and a rapid response team, whose job is to minimize the impact of an assault. When you plan, put in place procedures for your customer support and communication teams, not just for your IT professionals.