Distributed Denial of Service attacks, usually referred to as DDoS attacks, are designed to take websites, applications and systems offline by bombarding them with so much traffic that their servers are unable to cope. While these carefully coordinated and targeted attacks can cause huge disruption to businesses, there are ways to defend against them and in this post, we discuss what these are.
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How DDoS attacks are carried out
Before knowing how to defend against a DDoS attack, it is helpful to understand how they are carried out. In order to overwhelm a server with traffic, cybercriminals often need to infect and take control of thousands of other computers and online devices. This enables them to create a botnet, a network of compromised devices through which they are able to coordinate a mass attack, triggering all the machines to send repeated requests to a server at the same time. Unable to handle all these requests, the server slows down and can eventually crash, taking websites, applications or even entire systems offline.
The following tips can help protect your website or applications against DDoS attacks.
- Install an application firewall
Application firewalls are intelligent tools that monitor all the incoming traffic your website or application receives. They are designed to work as a gatekeeper, letting good traffic through while filtering out any traffic that might be malicious. For this reason, they are not just useful for protecting against DDoS attacks, but they can also prevent SQL injection and cross-site scripting (XSS) attacks as well.
An application firewall works by looking for patterns in the behaviour of incoming traffic. In the case of DDoS attacks, if traffic is coming from unusual sources, in fast succession or in higher-than-expected volumes, the tool will be triggered to block these requests. At the same time, firewalls also have access to libraries of malicious and compromised IP addresses, so if traffic is identified as coming from any of these, it too will automatically be blocked.
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- Set up rate limiting and traffic throttling
Two quite similar techniques you can use to protect against DDoS attacks are rate limiting and traffic throttling, both of which can be used to control the amount of traffic your server receives. Rate limiting, as the name suggests, allows you to limit the rate at which requests are processed. If you set this to 100 requests per minute, for example, any requests above this figure would be blocked. While this can prevent mass-scale DDoS attacks from having an impact, it is important to set your limit to one that your server can effectively handle and which won’t, under normal circumstances, block your visitors from using your site or application.
Instead of controlling the number of requests, traffic throttling is used to manage how much data is transferred. In other words, it limits the speed at which data is transmitted to one which your website or app is comfortably able to handle. While this will stop your server from crashing, it may reduce your loading times and affect performance during busy periods.
- Load balancing
Load balancing is often part of the service provided by a web host and your ability to take advantage of it may depend upon the hosting solution that your website or app is using. What load balancing does is distribute traffic coming to your website or applications across different servers, ensuring that individual servers can’t be overwhelmed. Depending upon your host and your hosting setup, this can be done across different servers within a data centre or even across different data centres.
What load balancing does is ensure that there is always capacity available for your website or application to deal with spikes in traffic. This is great for busy websites or applications with high processing demands at any time, however, it also provides increased resilience against DDoS attacks.
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- Use a content delivery network (CDN)
A lot of website owners already use content delivery networks as a means to speed up their site’s loading times. Essentially, CDNs store a site’s static content on servers around the globe so that it can be delivered more quickly to different geographic locations. For instance, if your site is hosted in the UK and uses a CDN, users in other parts of the world will enjoy quicker loading times as the static data won’t have to travel all the way from the UK, just the nearest CDN server.
The advantage in terms of defending against DDoS attacks is that by using a CDN, you are reducing the amount of data your own server needs to send when your website is requested. Whilst this doesn’t prevent a DDoS attack from taking place, it does lessen its impact on your server, making it more resistant to an attack.
- Third-party DDoS protection
There are a growing number of third-party providers that offer dedicated DDoS protection services for businesses. These services use a range of methods to prevent attacks and mitigate any impact. Some of these include DNS firewalls, IP blacklist and HTTP header filters and JavaScript challenges that are designed to block botnet requests while letting legitimate requests through. Additionally, some of these services operate as a reverse proxy that sits between your server and your visitors and can absorb the traffic sent to your server by a DDoS attack. Cloudflare, for example, has data centres in 120 countries with a total network capacity of 280 Tbps, enough to protect against very large attacks. While many of the DDoS protection services come with a price tag, some providers offer free basic packages that can be worthwhile taking advantage of.
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- Choose a secure web host
Ideally, your web host should be your first port of call when looking to defend against DDoS attacks. A good host will implement their own DDoS protections as well as deploying application firewalls and load balancing. Additionally, they will enable you to make use of advanced tools like Imunify360, designed for Linux servers, which includes a web application firewall and blocks malicious IP addresses, while letting you implement modules like mod_evasive on Apache servers. Your host should also provide you with 24/7 technical support so that, should a DDoS attack happen, you will have an expert on hand to help you remediate the situation.
Conclusion
DDoS attacks are not only used by criminals but increasingly by state-sponsored hackers looking to disrupt national infrastructure and its supply chain. While these attacks can take websites and applications offline for long periods and cause immense disruption, there are ways to defend against them. Hopefully, from reading the tips above, you’ll now have a better understanding of how to put these measures into place.
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