DoS vs. DDoS attacks: what’s the difference?

A denial-of-service attack seeks to take systems or websites offline via traffic floods and malicious requests. These attacks can involve single sources (DoS attacks) or leverage thousands of bots in distributed denial-of-service (DDoS) attacks. A denial-of-service (DoS) attack comes from a single source, overwhelming a system to disrupt service. A distributed denial-of-service (DDoS) attack uses multiple sources, making it harder to block and more damaging.

Both attack types are common and dangerous but they are not identical. This article will help you understand DoS vs. DDoS attacks and implement measures to safeguard your network.

What is a DoS attack?

Denial of Service (DoS) cyber-attacks attempt to disrupt operations by flooding targets with malicious traffic.

DoS attacks could target servers, web applications, or entire networks. They always aim to overwhelm victims, leading to a denial of service. When this happens, downtime or performance problems result.

Unlike DDoS attacks, DoS attacks originate from a single machine. Attackers do not leverage botnets to amplify their attacks. As a result, DoS attacks are simple to organize but generally less damaging for victims. Even so, the consequences can be severe.

All networks have processing thresholds. A denial-of-service attack exploits the resource limits of targeted systems. Beyond that point, servers fail to process and redirect packets and applications collapse due to excessive requests.

When a DoS attack succeeds, servers and apps become overloaded. They cannot respond to legitimate traffic and may become unavailable to users.

DoS examples:

The Ping of Death DoS attack sends many Internet Control Message Protocol (ICMP) pings to target devices. These pings exceed the maximum allowable packet size for ICMP pings. Packets are also fragmented, allowing attackers to breach network security barriers. Reassembling many packets causes buffer overflows and crashes the target system.

The teardrop attack exploits IP packets. This DoS attack uses fragmented IP packets with irregular offset values. This packet design confuses targeted servers, causing buffer overflows, freezes, and system-wide crashes.

What is a DDoS attack?

A Distributed Denial of Service attack (DDoS) is a more sophisticated form of DoS attack.

A DDoS attack compromises multiple systems, using bot networks to coordinate mass-scale attacks. This attack model allows criminals to direct large amounts of traffic at targeted networks. Because of this architecture, a DDoS attack will generally cause more damage than a standard DoS attack.

DDoS attacks use malware to infect exposed devices. Malware installs bot agents, which are connected to centralized command and control centers. Attackers coordinate attacks from this control center, enabling them to send HTTP requests and UDP floods until target networks collapse.

Organizations may be able to detect a DDoS attack before it becomes critical. Symptoms include traffic spikes, anomalous bandwidth consumption patterns, slow response times, and service interruptions. When these problems occur together, a DDoS attack is likely underway.

Distributed denial-of-service attacks are often launched by groups connected with political causes or terrorism. However, criminals also use DDoS techniques to threaten companies and extract ransom payments. Mounting a DDoS attack is also becoming easier as botnet kits become available on the Dark Web.

Example: The Slowloris DDoS attack gradually overwhelms its target. Attackers send partial HTTP requests from many bots, creating open HTTP connections that attackers maintain via small transfer requests. Eventually, attackers breach the website's concurrent connection limit, taking the site offline.

Types of DoS and DDoS attacks

There are many ways to flood targets with malicious traffic. Organizations need to guard against all common DDoS and DoS attack methods. The list below summarizes the main varieties:

• DoS floods. The simplest form of DoS attack. Attackers send a flood of requests to targets. They could use ICMP pings, SYN requests, or UDP queries. Targeted networks become overwhelmed by processing requests, resulting in performance dips and crashes.
• Protocol attack. A protocol attack leverages the methods used to transfer data. Attackers may send deliberately malformed ping packets, causing data processing spikes. They can also fragment packets into many pieces that target servers cannot reassemble.
• Volumetric attacks. These attacks rely on sheer data volume to overwhelm victims. Volumetric attacks may use compromised DNS servers or Network Time Protocol transfers to amplify attacks.
• Application layer attacks. This DDoS attack targets web applications. Criminals flood applications with HTTP requests. They may also use the Slowloris technique, sending partial HTTP requests to confuse targets.
• Reflection attacks. Attackers use third-party servers to "reflect" traffic at targeted networks. For example, so-called Smurf attacks use reflected ICMP echo requests, while Fraggle attacks use UDP packets. Reflection attacks conceal the attacker's identity, making it harder to identify threats and mitigate attacks.
• Multi-vector attacks. DoS and DDoS attackers may use multiple techniques to amplify traffic flows and complicate responses. For example, attackers could combine the teardrop attack and Slowloris HTTP traffic to take down a targeted website.

What is the difference between DoS and DDoS?

Comparing DoS and DDoS attacks is about more than scale. These two critical cyber threats operate slightly differently, have varying symptoms, and cause different consequences for victims. Here are the main differences to help you plan effective responses:

Source

DoS attacks originate from a single system. Because attackers direct traffic via botnets hosted by multiple systems, a DDoS attack emerges from many directions.

Speed

DoS attacks are usually less intense. This is because traffic volumes are generally lower. A DDoS attack can grow rapidly, quickly exceeding the target's ability to respond.

Ease of detection

A DoS attack tends to be easier to defeat as it comes from a single source. Blocking the source tends to neutralize the attack. DDoS attacks from multiple sources are harder to stop. Taking out one bot is no use as replacements constantly become available.

Scale

A DoS attack involves amounts of traffic from a single system and are limited by the capabilities of a single source. DDoS attacks operate on a far larger scale and are capable of taking out the networks of large companies.

Complexity

A single criminal can launch a DoS attack quickly and at a low cost. DDoS attacks were once harder and more expensive, but DDoS-for-hire services and botnet kits make them affordable. Now, criminal groups and state actors often carry out these attacks.

Mitigation

Targets can prevent most DoS attack types by blocking the source. Mitigating a DDoS attack is harder. To prevent DDoS attacks victims must filter traffic, apply targeted rate limiting, and scan for bot activity across the whole network.

Consequences

A DoS attack can take out devices or apps but rarely troubles networks as a whole. DDoS attacks take websites and networks offline, even if they have sophisticated security measures in place.

How can you prevent DoS and DDoS attacks?

All organizations can fall victim to a DDoS or DoS attack, compromising network performance and website availability. Detecting and mitigating denial-of-service attacks is a cybersecurity priority.

Here are some tips to prevent DDoS attacks and secure your network:

• Implement network redundancy. Redundancy distributes resources across many locations. When attackers take out servers or databases, redundant capacity takes up the slack, allowing networks to function as normal.
• Operate multi-tiered network security measures. Defend networks in depth to manage unexpected traffic spikes. Configure firewalls to detect suspicious traffic before volumetric attacks materialize. Use threat detection tools to root out bots and identify DoS attacks.
• Add Web Application Firewalls (WAFs). Place a WAF in front of web-facing assets. These firewalls filter HTTP requests and reliably block application layer attacks.
• Shrink the attack surface. Larger attack surfaces are more vulnerable to traffic-based attacks. Make life hard for DoS attackers by closing unused ports, patching network devices, and minimizing the number of services you use.
• Use proactive traffic monitoring. Monitoring traffic is the only reliable way to flag DDoS attacks. Track baseline activity patterns and investigate deviations from the norm. Respond swiftly to traffic spikes and assume they represent a security threat. Even if there is no threat, proactive monitoring means you are ready to act.
• Wargame DoS and DDoS attacks. During security planning, workshop potential denial of service scenarios. Create an incident response plan to isolate affected servers or applications and keep services running smoothly. Incident playbooks ensure systematic responses from a well-drilled security team.
• Understand DDoS symptoms. Train employees to identify the tell-tale signature of DDoS attacks. For instance, employees may notice slowdowns or unavailable services before security teams.
• Employ traffic management tools. Rate limiting allows security teams to limit users involved in denial-of-service activities. Connect monitoring to throttling and limiting tools, and quarantine suspicious connections before attacks occur.
• Use third-party security partners. Websites often use third parties to screen and manage traffic (capacities that smaller businesses often lack).

It is not always possible to completely prevent denial-of-service attacks. Sometimes, a DDoS attack mobilizes sufficient resources to breach defenses and compromise networks. Companies should plan for worst-case scenarios while taking action to minimize DDoS risks.