DDoS attacks are becoming a bigger and bigger threat to online services, overwhelming servers with malicious traffic and resulting in costly downtime.
Recent attacks have seen unprecedented traffic volumes – Cloudflare mitigated a 2.5 Tbps DDoS attack in 2022, and Google Cloud documented a Layer-7 attack peaking at 46 million requests per second.
Such multi-terabit attacks show we need robust, multilayered defences: “Implementing scalable and resilient multilayered DDoS protection solutions is key to this”. Among the many DDoS protection techniques, one important layer is the proxy server.
By sitting between clients and backend systems, proxies can filter, absorb, and mitigate malicious traffic before it hits critical infrastructure, so DDoS attacks can be mitigated and prevented.
This article explains how proxies provide an extra layer of protection against DDoS attacks and best practices for proxy server security in this context.
What are Proxies and Their Role in Defence?
A proxy server is an intermediary network node that sits between clients (end users or devices) and origin servers.
In practice, a reverse proxy is placed at the edge of the network to receive incoming requests and forward them to backend servers. (This is different from a forward proxy, which sits on the client side to mediate outgoing requests.)
Reverse proxies are often called “traffic cops”: they terminate client connections, apply security and caching logic, and then relay requests to the origin.
By directing all traffic through proxies, organisations create a choke point where security policies can be enforced. In cyber defence architectures (e.g., Zero Trust networks), proxies “are strategic choke points, where content filtering, deeper inspection of traffic, and robust proxy server security can be applied”.
In short, a proxy can inspect, filter, or transform client requests before they hit the protected servers, so it’s the perfect place to implement DDoS protection techniques like traffic scrubbing and rate limiting.
How Proxies Enhance DDoS Protection
One of the biggest benefits of using a reverse proxy is that it hides the origin server’s IP address. An attacker launching a DDoS attack targets an IP address.
If the origin’s IP is not exposed, attackers can only send their malicious traffic to the proxy’s address. This makes targeted DDoS attack prevention much harder.
For example, Imperva says when connections are routed through a reverse proxy, “connections are first terminated by the proxy and then reopened with the backend server.
As a result, your origin server’s IP address is masked. This makes it much harder for attackers to get in and launch a direct-to-IP denial-of-service attack. Cloudflare notes that a reverse proxy “never has to reveal the IP address of its origin server(s).
This makes it much harder for attackers to target…a DDoS attack. In effect, the proxy server becomes a sacrificial lamb that can be more heavily protected and scaled up, while the origin server stays behind the scenes.
Distributing and Scrubbing Traffic
Another benefit is that proxies can scrub incoming traffic and distribute load to mitigate volumetric DDoS. Reverse proxies and CDNs are typically deployed in multiple locations (often using Anycast networks) so that incoming traffic is spread across a mesh of proxy nodes.
Imperva describes this “traffic scrubbing” role: Reverse proxies are ideally situated to scrub all incoming application traffic before it’s sent on to your backend servers.
In a DDoS scenario, the load is shared among many proxies: incoming traffic is distributed among a mesh of reverse proxy servers during a DDoS attack to deflate its overall impact. This dispersion ensures no single backend is overwhelmed.
Likewise, Zscaler (a security platform) observes that proxies “can help distribute or filter the load” during a high-volume attack, effectively mitigating the impact of a DDoS attack.
In practice, proxy clusters or CDNs at the network edge serve as large traffic “shock absorbers”: they route abusive traffic through redundant paths and even blackhole malicious streams without interrupting legitimate user connections.
The combination of traffic distribution and filtering at the proxy layer is a proven DDoS attack mitigation technique.
Filtering and Blocking Malicious Requests
Proxies also act as powerful gatekeepers for filtering malicious requests. Because all external traffic flows through the proxy, it can enforce security rules and inspect each request.
For example, many enterprises place a Web Application Firewall (WAF) on the proxy. A WAF operates as a reverse proxy and examines HTTP/HTTPS traffic against rule sets to detect and block attacks.
Cloudflare explains that a WAF “may act as a reverse proxy, protecting the targeted server from certain types of malicious traffic”. In essence, the proxy can be configured to drop or challenge suspicious connections (e.g., automated flood requests) while letting normal users through.
Zscaler likewise notes that by funneling traffic through a single checkpoint, administrators can apply “real-time filtering and inspection routines to sniff out malicious activity”.
In short, the proxy does early traffic inspection: IP allowlists/denylists, geofencing, source rate limiting, or CAPTCHA tests can be applied by it. It’s one of the main DDoS defense mechanisms of this filtering level: the bad traffic is blocked in the proxy, so the backend isn’t loaded.
Some of the proxies monitor client activity and slow down or block all IP blocks with DDoS-like activity. Proxies, in short, help in preventing DDoS attacks by filtering out bad packets even before they reach the main services.
Caching and Performance Offloading
Beyond filtering, many proxies improve performance via caching, which helps with DDoS mitigation. A caching proxy stores copies of frequently requested content (static web pages, images, files, etc.) and serves them directly to clients without hitting the origin server.
During a DDoS attack or sudden traffic surge, cached responses can absorb much of the load.
For example, NGINX (a popular reverse proxy and load balancer) can be tuned to “absorb much of the traffic spike…by enabling caching and setting certain caching parameters to offload requests from the backend”.
In other words, if an attacker floods the site with repeated requests for the same URLs, the proxy can return cached (or “stale”) content instead of forwarding every hit to the origin. This reduces server CPU and bandwidth consumption, smoothing out spikes.
CDNs (which are networks of proxy caches) cache content globally so most user requests never reach the origin. By serving cached content to legitimate users even under attack, a proxy layer increases resilience.
Caching also works hand-in-hand with content delivery. Many reverse-proxy setups use anycast DNS to direct users to the nearest proxy node, reducing latency and localizing traffic.
The proxied cache not only speeds up legitimate traffic but keeps the user experience acceptable even if part of the network is under attack.
All of these benefits – reduced backend load, preserved performance, and bandwidth relief – help with DDoS attack mitigation.
As Imperva notes, reverse proxies deployed in multiple geographic locations can compress and cache content to “reduce page load times and improve user experience,” which in turn lightens the load on origin servers.
Load Balancing and Failover
Reverse proxies also provide load balancing among multiple servers, which helps with DDoS defense. Because the proxy manages traffic routing, it can spread each client session across several backends.
If one server starts to struggle under load, the proxy can send new requests to healthier nodes. By spreading sessions, the reverse proxy can distribute the load efficiently and improve user experience and high availability.
Crucially, if a server goes down during an attack (or for any reason) the proxy can reroute traffic to others (“failover”) and keep the service up. This means an attacker must overwhelm all backend resources at the same time, much harder.
In short, the built-in load balancing of proxies helps with DDoS defense by making no single resource a point of failure.
Rate Limiting and Connection Controls
Many proxies support granular rate limiting and connection policies. For example, an admin can configure a proxy to limit the number of connections or requests from any one IP within a time window.
If a client exceeds the threshold, further requests can be dropped or delayed. This is a classic DDoS attack prevention measure. Cloudflare has rate-limiting rules that apply at the proxy, while NGINX has limit_conn and limit_req directives to cap connections and request rates per client IP.
Geonode (a proxy service provider) says enabling rate limiting on the proxy “will not allow any traffic to reach your proxied site after the set period,” so bot-generated floods are automatically blocked.
By throttling suspicious bursts, proxies give admins time to react before an outage. Combined with filtering rules, rate limiting at the proxy is a great way to slow down and neutralize many DDoS attacks.
Ensuring Proxy Server Security
While proxies add DDoS protection, the proxy servers themselves must be secure. This is proxy server security hygiene: since proxies are exposed to the internet and handle all incoming traffic, they become a target.
Best practices include keeping proxy software up to date, restricting management interfaces, and placing proxies in a segmented security zone. In a layered security approach, proxies often form part of a zero-trust perimeter.
As Zscaler succinctly describes adding proxies to zero trust as “adding a strict level of authentication between external requests and your systems,” of course, translating to “robust proxy server security” in the real world, making the proxy stronger with the implementation of firewalls, intrusion-detection monitoring, and strict access controls.
IT professionals also have to seek anomalies in the proxy logs (like repeated failed requests) and keep the os and applications running on the proxy with no unpatched vulnerabilities.
In reality, the proxy level itself needs to be defended as hard as the origin servers since a compromised proxy is an attack vector. Proxies are used by the majority of companies in the cloud or with DDoS defense services (CDNs, managed WAFs, etc) so the company can leverage the scale and experience of the service provider.
Whether on premises or cloud-based, careful configuration is key. For example, ensuring SSL/TLS is terminated at the proxy and only legitimate traffic is forwarded helps prevent bypass attacks. By keeping proxy server security strong, organizations ensure the proxy layer adds to DDoS defense rather than introducing new weaknesses.
Conclusion
Proxy servers create a powerful second line of defense against DDoS attacks as part of a well-rounded defense strategy. Placed between the Internet and back-end servers, proxies can conceal source IPs, clean and filter out malicious traffic, cache and normalize bursts with cached content, and load balance between resources.
All these functions make the majority of DDoS defense techniques—from IP masking and traffic cleaning to rate limiting and WAF integration—enforceable on the proxy layer.
In practice, a well-set-up reverse proxy or Content Delivery Network can soak up or bounce most of the attacking traffic and still leave the legitimate users accessible even when under assault.
Observe, however, that proxies are only part of the answer for the prevention of DDoS attacks. Proxies would work optimally as part of multi-level strategy including monitoring, incident response plans, etc.
But by enhancing proxy server security and employing proxies effectively, IT administrators can make a significant difference to their ability to block DDoS attacks.
Where uptime is valuable down to the millisecond, proxies offer the extremely robust “shock absorber” against traffic spikes and a potent defense against malicious flood attacks.
Featured Image – Freepik
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