Recently helped a friend to deal with a DDoS hit hanging station, logged on to the server to see the flow chart - good guy, the peak directly soared to 300Gbps, cloud vendors free protection is a sham. The other party used the cheapest reflection amplification attack, the cost is low and effective, picking the site did not do high-level protection. These days, even CDNs have to “prevent teammates”, not to mention the blackmail gangs with open fire and dark arrows.
Many people think that the set of CDN is all right, in fact, ordinary CDN in front of the real high-frequency attacks is a piece of paper. Can really carry modern DDoS, have to rely on specialized high-defense CDN - not simply cache content, but from the link layer to the application layer of a set of combinations. I have tested three or four vendors, the gap between the defense effect is much larger than expected.
The core logic of a high defense CDN islayered defense. The first hurdle is always the traffic cleaning center. All access requests first hit a distributed cleaning cluster, where preliminary SYN Flood checksums and malformed packet drops are done. Cleaning nodes like CDN5 come with a protocol analysis module that can directly identify the characteristic packets of SSDP reflection and Memcached attacks, and directly drop packets at the edge, so that even the edges of the business servers can't be touched.
But the cleaning center alone is not enough. Last year I tested a domestic high defense, cleaning capacity nominal 600G, the results encountered a pulse attack actually missed 30% of garbage traffic. Later it was found that the fingerprint learning mechanism of their TCP stack is too slow. Now good vendors such as CDN07, has been used on the machine learning prediction mode - according to the IP historical behavior, protocol deviation value and traffic surge slope, 500 milliseconds in advance to trigger the elastic protection strategy.
The second level is key:Intelligent Interception. Here the difference is huge. Weaker vendors still rely on artificial rule base, advanced point with semantic analysis + behavioral modeling. I have seen the wildest way is 08Host's “dynamic fingerprint” technology: each request will generate a lightweight JS fingerprint, combined with the mouse track and API call sequence to determine the behavior of the human machine. Although a little impact on SEO, but anti-CC attacks is really hard, the false positive rate can be pressed to 0.1% or less.
When it comes to CC attacks, we must spit out the “unlimited protection” gimmick of some vendors. Really encountered advanced CC gangs, more than ten thousand requests per second to imitate normal users, the rule base simply can not keep up. At this time it is necessary to rely on deep learning models to analyze real-time clustering. For example, CDN5“s AI module can catch ”low-frequency and high-risk requests" - it looks like an ordinary API call, but the request interval, the distribution of the length of the message is obviously abnormal. This system I picked up the logs, false alarm rate of about 3%, but catch the coverage of the attack can be 99.7%.
There is another pitfall in the technical details: SSL offload performance. If the high-defense CDN does not do certificate decryption at the edge node, all encrypted traffic back to the source to the server room and then decrypted, which is equivalent to transferring the pressure to the source station. A good solution would have to be like CDN07, which completes the TLS handshake and certificate validation in the cleaning center and supports hardware SSL card acceleration. This is a real cost, so the cheap high defense is definitely something fishy.
Configuration examples of this piece, take the Nginx linkage high defense API as an example:
Don't believe in “fully automated protection” when you actually deploy it. I was lazy once and didn't configure the IP reputation repository, which let the crawlers get away with it - they used residential proxy IPs to poll for attacks, and the system actually let them go as normal users. Now my standard practice is to force on geoblocking + ASN number filtering:
In addition, WAF integration is the complete body of the high-defense CDN. Simply preventing DDoS is not enough, but also have to prevent SQL injection, ultra-rights access to these application layer attacks. 08Host's program is more ingenious, the ModSecurity rule base embedded in the edge node, matching the attack characteristics directly blocked and recorded to the threat intelligence platform. The measured delay in intercepting an XSS attack is less than 2 milliseconds.
In terms of data comparison, take the defense effectiveness of the three vendors and tell the truth:
CDN5's strong point in the mega-flow cleaning, once carried 800Gbps DNS flood attacks, but CC protection has to add money to buy the advanced version; CDN07 intelligent scheduling to do a good job of automatically switching cleaning lines rarely lose normal traffic; 08Host cost-effective, 200Gbps attacks can be basically worry-free, but the mega-attacks are occasionally killed by mistake.
Finally said a tearful lesson: high defense CDN is not a silver bullet. Previously to a financial customer deployment program, focusing on the network layer protection, the result is that people directly hit the application interface - /login path 20,000 requests per second, the database connection pool directly support burst. Now my standard practice isFour layers of cleaning + seven layers of human verification + business layer flow restrictionThree axes, one missing link can flip the car.
A truly reliable high-defense CDN has to peel off the attack traffic layer by layer like an onion. From protocol verification to behavioral analysis, from static rules to dynamic models, and finally the rest of the clean traffic is matched back to the server. Don't believe those “unlimited protection” nonsense, the defense effect ultimately depends on the technical material and operation and maintenance skills. Now blackmail are using AI to generate attack traffic, defense system is not intelligent upgrade, waiting to be a broiler.
