The somewhat illegal fix for NTP attacks

Jared Mauch jared at
Sat Feb 22 12:43:21 UTC 2014

On Feb 21, 2014, at 5:08 PM, Baldur Norddahl <baldur.norddahl at> wrote:

> Hi
> The following would probably be illegal so do not actually do this. But
> what if... there are just 4 billion IPv4 addresses. Scanning that
> address-space for open NTP is trivially done in a few hours. Abusing these
> servers for reflection attack is as trivial, hence the problem. How can we
> get the responsible parties to fix their NTP servers?
> Answer: DDoS them. With their own service.

One of the attacks that was mitigated the fastest was the SQL Slammer worm due to the broad impact it had across the internet.

The OpenNTP and OpenResolver projects provide inventories of these servers for operators to take action and to take to their customer cone.

> Or it could be a DDoS defense. As a victim of an ongoing NTP reflection
> attack, you know exactly the IP-addresses of the vulnerable NTP servers
> used to attack you. Make them stop by sending back forged NTP packets, so
> they use up their available bandwidth to DDoS each other instead of you.

> This could even be automated. If you let them attack their next-hop as
> discovered by traceroute, it might not even be illegal or harmful. They
> will only bring down their own link, do no more harm to the internet at
> large and they can fix it by stopping the NTP service. If they are part of
> an ongoing DDoS attack it is just self defence to shut them down in the
> least harmful way possible.

Do you have a letter from the local law enforcement or legal counsel on this topic?  If so, can you please share it with the class or submit a presentation to an upcoming conference on this?

- Jared

More information about the NANOG mailing list