How to Prevent DDoS Attacks: 12 Best Practices

Distributed denial-of-service (DDoS) attacks aim to overwhelm servers and network infrastructure by flooding them with traffic from multiple sources. This guide covers the most effective ways to help prevent DDoS attacks and keep your website or application online.

By implementing these 12 best practices, you can significantly improve your DDoS protection:

• Use a cloud-based DDoS mitigation service
• Enable firewall blacklisting capabilities
• Configure web application firewall rules
• Distribute incoming traffic across multiple servers
• Limit open ports and unused protocols
• Optimize application performance
• Implement SSL to encrypt traffic
• Mask the origin server IP address
• Monitor traffic for attack patterns
• Have an incident response plan ready
• Use an anycast content delivery network
• Maintain hardware/software redundancy

Now let’s explore each of these DDoS prevention techniques in more detail.

What is a DDoS Attack and How Does it Work?

Before we take at look into prevention methods, it’s important to understand what a DDoS attack is and how cybercriminals leverage them against websites and applications.

A distributed denial-of-service (DDoS) attack aims to make a targeted server, application or network unavailable to legitimate users by overwhelming it with traffic from multiple sources. These flooded requests will effectively “clog up” the bandwidth of the recipient, preventing access for users.

DDoS attacks work by leveraging a botnet – a network of devices infected with malware that allows them to be controlled remotely. The operator will order these compromised devices to send requests to the same target at once, creating a volume of traffic the server cannot handle.

There are three main types of DDoS attack vectors:

• Volumetric Attacks – Floods the network bandwidth via UDP, ICMP floods, or other spoofed-packet attacks
• Protocol Attacks – Targets network infrastructure like firewalls and load balancers via malformed packets
• Application Layer Attacks – Overloads applications via GET/POST floods, DNS query floods etc.

Understanding the variety of DDoS attack types is key for learning how to prevent them effectively. Now let’s look at 12 techniques to protect against these threats.

1. Use a Cloud-Based DDoS Mitigation Service

The most effective way to guard against DDoS attacks is by using a cloud-based mitigation service designed specifically to filter out and absorb malicious traffic before it can reach your infrastructure.

Providers like Cloudflare offer DDoS protection by routing all traffic through their global network of data centers which can identify and isolate floods of bogus requests. By the time requests reach your origin servers, legitimate traffic is all that remains.

Cloud-based services also have the benefit of massive bandwidth and mitigation capacity to absorb even the most extreme DDoS attacks exceeding 1 Tbps. Compare this to appliances which may become overwhelmed themselves.

2. Enable Firewall Blacklisting Capabilities

Firewalls serve as the gatekeepers inspecting traffic as it enters your network environment. Most modern firewalls include blacklisting capabilities that allow blocking known malicious IP addresses.

Enable this functionality and ensure the firewall blacklists are automatically updated. Maintain an allowlist of legitimate IP ranges from partners as well to minimize false positives.

While blacklists don’t prevent zero-day attacks, they filter out requests from IPs known to propagate threats like DDoS bots. Firewalls also analyze traffic headers and patterns which aids detection.

3. Configure Web Application Firewall Rules

A web application firewall (WAF) applies rulesets to filter out suspicious traffic specifically targeting websites and apps vs the network itself. Much like blacklists, customized WAF policies improve protection by blocking traffic matching threat characteristics.

Common WAF policies involve things like maximum requests per session, input lengths, file types etc. Also restrict unused HTTP methods, implement CAPTCHAs, and limit login attempts per source IP where applicable.

The advantage of WAF rules over traditional firewalls is the application-layer visibility enabling precision blocking of DDoS vectors like layer 7 GET/POST floods. Used together, both firewall and WAF policies maximize coverage across traffic types.

4. Distribute Incoming Traffic Across Multiple Servers

One of the best ways to prevent successful DDoS attacks is distributing traffic loads using a technology like anycast to route requests across multiple servers in data centers around the globe.

This makes it impossible for attackers to target one centralized point of failure. Even if one node becomes overwhelmed, others absorb the excess load to prevent outages while threats are mitigated.

A variety of network protocols like DNS anycast, GSLB, or CDNs leverage this method of traffic distribution to stop DDoS attacks by eliminating single targets and improving capacity to handle larger floods.

5. Limit Open Ports and Unused Protocols

While things like firewall policies proactively filter traffic, reducing your attack surface area limits vectors threats might exploit in the first place. One way to accomplish this is closing down unnecessary open ports and disabling unused protocols.

For example, if you only operate web servers, there is likely no reason to have SMB, SNMP, or FTP ports open on those same systems. Many applications include features that enable additional protocols unnecessary for their core function.

The more ports left open, the more potential entry points for DDoS attacks. Use port scanning tools like Nmap to inventory open ports and harden configurations around what is absolutely necessary for business functions.

6. Optimize Application Performance

If applications struggle to handle average traffic loads under normal conditions, they will likely crash faster when bombarded by a DDoS attack. Make sure apps are optimized for performance.

Common optimizations include things like database indexing, caching, compression, code optimization etc. Bottlenecks like database queries, load-intensive scripts, Sessions, and large file loads are often key targets.

The more efficient your apps, the higher the traffic volumes they can handle before becoming overwhelmed. Performance optimizations also speed up recovery times when attacks strike by improving baseline capabilities.

7. Implement SSL to Encrypt Traffic

Encrypting traffic with SSL or TLS forces DDoS bots to establish the added handshake in order to interact with target sites and applications. This provides an advantage over unencrypted apps.

For attackers utilizing techniques like spoofed IP packet floods, the encryption handshake requires more effort to complete since they cannot easily falsify legitimate encrypted requests as quickly. This can act as a buffer against rapidly increasing traffic levels.

SSL also protects web traffic integrity which prevents bots from directly targeting application vulnerabilities as easily via common injection attack payloads. Require encryption across all sites and apps wherever possible.

8. Mask the Origin Server IP Address

If attackers directly know and can see the IP address and fingerprints of your web server or application host they may more easily isolate and target it with traffic floods. Prevent this using network address translation (NAT) and IP masking.

NAT routes traffic through intermediary routers and firewalls, partitioning internal private IPs from external public IPs that the outside world sees. The source of inbound traffic gets replaced to obscure your infrastructure.

IP masking prevents the server IP from appearing in areas like email headers and web logs, instead replacing it with IPs of edge NAT devices to keep your origin server concealed.

9. Monitor Traffic for Attack Patterns

Quickly detecting ongoing DDoS attacks or reoccurring attack patterns targeting your infrastructure is important for rapid mitigation. Monitor traffic flows across servers, routers, firewalls, WAFs, and applications.

Use network monitoring software to set thresholds and alerts for abnormal traffic levels, blacklisted endpoints, resource utilization spikes beyond historical peaks, error rates, status code anomalies etc.

Data center monitoring provides macro visibility while host-based application monitoring highlights per node issues for faster attack insights. The sooner an attack is detected, the quicker countermeasures may engage before major disruption.

10. Have an Incident Response Plan Ready

Even with proactive defenses, DDoS attacks may still overwhelm resources at times. This is why having an incident response plan is critical – outlining steps IT teams should take during an attack to isolate and mitigate issues faster.

Response plans designate specific tasks and communication workflows to verify and escalate ongoing attacks, reroute traffic, activate alternative resources, coordinate with providers, notify stakeholders etc.

Well defined plans avoid chaos, speeding up your organization’s ability to neutralize DDoS disruptions. Make sure all members understand their responsibilities so everyone reacts properly.

11. Use an Anycast Content Delivery Network

As outlined earlier, distributing attack traffic across a mesh of servers improves mitigation capacity vs individual systems. CDNs supercharge this concept using Anycast addressing allowing requests to be load balanced across multiple data center points of presence (POPs).

This prevents attackers from targeting one location, requiring they overwhelm numerous globally dispersed POPs simultaneously which most botnets cannot achieve at once. This buys time for detection and filtering rules to engage as needed regionally.

Combing Anycast CDNs with cloud-based DDoS scrubbers creates a layered defense spreading traffic across a web of locations and filtering it before reaching your infrastructure for maximum uptime protection.

12. Maintain Hardware/Software Redundancy

If all else fails and attack traffic manages to take down your primary servers or network hardware like routers and switches, redundancy mechanisms ensure you can failover to backup replacement devices instantly while under stress.

From hot standby failover firewalls and load balancers to clustered application servers capable of redistributing requests during member outages and VM auto scaling groups – be prepared for equipment failures.

Hardware redundancy options range from cold spare appliances to active-active network links with automatic switching when connections go down. Take stock of all Single Points of Failure (SPOF) and address them.

Key Takeaways: Protecting Against DDoS Attacks

Guarding against distributed denial-of-service attacks involves a combination of proactive and reactive measures across network, infrastructure, and application layers. Key takeaways include:

• Cloud scrubbing services filter large volumetric and application layer attacks closest to the source before your environment is directly hit
• Firewalls, IDS/IPS, and WAF blacklists preemptively block known malicious IPs and traffic patterns
• Anycast CDNs increase DDoS resiliency by distributing attacks across global server infrastructure
• Performance improvements increase workload capacity before saturation
• Incident response plans speed up diagnosis and disaster recovery when overwhelmed

No solution eliminates DDoS risk entirely. However using tools like cloud-based mitigation combined with application efficiency gains provides the greatest chance of remaining online when faced with large scale attacks.

Prioritizing DDoS prevention makes it considerably harder and more resource intensive for attackers to successfully disrupt infrastructure and internet-facing assets – reducing risk exposure over the long run.

Neil Beckett

Neil is an accomplished web, designer and developer with over 15 years of experience in creating and optimizing websites for small businesses and online entrepreneurs. Read full bio

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