The DDoS That Almost Broke the Internet

The DDoS That Almost Broke the Internet

March 27, 2013

The New York Times this morning published a story about the Spamhaus DDoS attack and how CloudFlare helped mitigate it and keep the site online. The Times calls the attack the largest known DDoS attack ever on the Internet. We wrote about the attack last week. At the time, it was a large attack, sending 85Gbps of traffic. Since then, the attack got much worse. Here are some of the technical details of what we've seen.

Growth Spurt

On Monday, March 18, 2013 Spamhaus contacted CloudFlare regarding an attack they were seeing against their website spamhaus.org. They signed up for CloudFlare and we quickly mitigated the attack. The attack, initially, was approximately 10Gbps generated largely from open DNS recursors. On March 19, the attack increased in size, peaking at approximately 90Gbps. The attack fluctuated between 90Gbps and 30Gbps until 01:15 UTC on on March 21.

The attackers were quiet for a day. Then, on March 22 at 18:00 UTC, the attack resumed, peaking at 120Gbps of traffic hitting our network. As we discussed in the previous blog post, CloudFlare uses Anycast technology which spreads the load of a distributed attack across all our data centers. This allowed us to mitigate the attack without it affecting Spamhaus or any of our other customers. The attackers ceased their attack against the Spamhaus website four hours after it started.

Other than the scale, which was already among the largest DDoS attacks we've seen, there was nothing particularly unusual about the attack to this point. Then the attackers changed their tactics. Rather than attacking our customers directly, they started going after the network providers CloudFlare uses for bandwidth.

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While we don't have direct visibility into the traffic loads they saw, we have been told by one major Tier 1 provider that they saw more than 300Gbps of attack traffic related to this attack. That would make this attack one of the largest ever reported.

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The Full Impact of the Open Recursor Problem

At the bottom of this attack we once again find the problem of open DNS recursors. The attackers were able to generate more than 300Gbps of traffic likely with a network of their own that only had access 1/100th of that amount of traffic themselves. We've written about how these mis-configured DNS recursors as a bomb waiting to go off that literally threatens the stability of the Internet itself. We've now seen an attack that begins to illustrate the full extent of the problem.

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Unlike traditional botnets which could only generate limited traffic because of the modest Internet connections and home PCs they typically run on, these open resolvers are typically running on big servers with fat pipes. They are like bazookas and the events of the last week have shown the damage they can cause. What's troubling is that, compared with what is possible, this attack may prove to be relatively modest.

As someone in charge of DDoS mitigation at one of the Internet giants emailed me this weekend: "I've often said we don't have to prepare for the largest-possible attack, we just have to prepare for the largest attack the Internet can send without causing massive collateral damage to others. It looks like you've reached that point, so... congratulations!"

At CloudFlare one of our goals is to make DDoS something you only read about in the history books. We're proud of how our network held up under such a massive attack and are working with our peers and partners to ensure that the Internet overall can stand up to the threats it faces.

Full post and charts: The DDoS That Almost Broke the Internet - CloudFlare blog

See also:
Spamhaus DDoS grows to Internet-threatening size | Ars Technica
That Internet War Apocalypse Is a Lie - Gizmodo

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