DDoS attacks, such as those that flood server resources with fraudulent requests, can render legitimate users unable to access the site. In severe cases, this can lead to business interruptions, financial losses, and even damage to brand reputation. Faced with this threat, CDNs (Content Delivery Networks) have become the preferred defense for many businesses and individuals because they can distribute website content globally and alleviate traffic pressure. However, many people misunderstand the protective capabilities of CDNs, particularly the belief that using a CDN can completely prevent DDoS attacks. This is not entirely accurate.

　　The core function of a CDN is to cache website content on node servers closest to the user. When a user accesses a website, the request is directed to the nearest CDN node instead of directly to the origin server. This reduces pressure on the origin server, improves access speed, and distributes traffic across a distributed network. For standard access requests, a CDN can significantly improve the website experience. However, when facing DDoS attacks, a CDN's protection capabilities primarily manifest in two aspects: distributed stress resistance and traffic filtering. Distributed stress resistance means that attack traffic is not concentrated entirely on the origin server, but is distributed across CDN nodes worldwide. Each node receives only a portion of the traffic, reducing the risk of origin server downtime. Traffic filtering relies on the CDN provider's built-in security mechanisms to minimize the impact of attacks on services by identifying abnormal requests, limiting access frequency, and blocking malicious IP addresses or request patterns.

　　While CDNs play an important role in defending against DDoS attacks, they cannot completely prevent all types of attacks. First, CDNs primarily specialize in combating large-scale network-layer attacks, such as SYN floods and UDP floods, which overwhelm servers with a massive number of requests. If the attack scales significantly, exceeding the bandwidth or computing power of CDN nodes, it may still impact the origin server. Second, application-layer attacks (such as HTTP floods) are more subtle, mimicking normal user behavior by sending large numbers of requests. These attacks often bypass the CDN's basic protection mechanisms because the requests appear to be legitimate traffic, requiring more complex rules and manual intervention to effectively identify and block them. Furthermore, attackers may directly target the origin server's IP address. If the origin server's IP address is not hidden or protected, the origin server may still be affected even if the CDN is functioning properly.

　　The effectiveness of the CDN's protection also depends on the provider's technical capabilities and configuration. High-quality CDN providers typically offer advanced protection features, including high-security IP, real-time traffic cleaning, behavioral analysis, and access control, mitigating the impact of DDoS attacks through a multi-layered strategy. For example, high-security IP automatically triggers protection policies upon the onset of an attack, isolating or discarding abnormal traffic. Real-time traffic cleaning analyzes request characteristics to filter out malicious requests, allowing only legitimate traffic to reach the origin server. Access control policies can limit the access frequency of individual IP addresses, preventing single-point attacks from excessively consuming resources. Furthermore, some CDNs support integration with web application firewalls (WAFs) to further enhance security by identifying specific attack patterns (such as SQL injection and XSS). These combined measures can effectively mitigate DDoS attacks in most cases, but they cannot guarantee 100% protection against all attacks.

　　Another factor that can affect the effectiveness of protection is the security policy of the origin server itself. If the origin server does not conceal its true IP address or has no firewall configured, attackers may still bypass the CDN and attack the origin server directly, even if the CDN implements front-end protection. This is a key aspect that many enterprises overlook when using CDNs. Therefore, CDN deployment must be coordinated with origin server security measures, including hiding real IP addresses, configuring firewalls, properly allocating bandwidth and resources, and monitoring traffic anomalies. Only with the joint protection of the front-end CDN and back-end origin servers can a relatively complete DDoS defense system be established.

　　Furthermore, a CDN's defense capabilities are closely related to the scale and type of attack. Small-scale, low-intensity attacks can usually be easily handled by the CDN, while large-scale, long-lasting, or hybrid attacks may still pose a certain impact. Hybrid attacks involve simultaneous attacks at the network and application layers, or attackers use multiple methods to circumvent security measures. These attacks require a coordinated response from the CDN, high-security IP addresses, WAFs, load balancing, and professional operations and maintenance teams. Therefore, when selecting a CDN service, enterprises should not only consider traffic distribution capabilities and acceleration effects, but also evaluate the provider's security protection capabilities, emergency response mechanisms, and attack mitigation experience.

　　Overall, CDNs offer significant advantages in combating DDoS attacks, distributing traffic pressure, filtering abnormal requests, and improving origin server stability. However, it cannot completely prevent all types and scales of DDoS attacks. Application-layer attacks and direct attacks against origin server IP addresses can still pose a threat. A sound approach is to consider CDN as part of an overall security strategy, integrating it with high-defense IP, WAF, firewalls, bandwidth redundancy, and traffic monitoring to form a multi-layered defense system, while also maintaining real-time monitoring of network traffic and emergency response capabilities. These measures can minimize the risk posed by DDoS attacks, but vigilance and continuous optimization of protection strategies are still necessary.

　　When selecting a CDN service, consider the provider's global node coverage, bandwidth resources, traffic scrubbing capabilities, protection rule flexibility, integration with origin servers, and operational support capabilities. Users should also regularly test protection effectiveness and simulate attack scenarios to ensure rapid response and mitigation in real-world situations. Through scientific configuration and a balanced strategy, CDN can be a crucial component of DDoS protection, but relying solely on it cannot completely eliminate risks.