Semi-urgent: Disable NTP replies?

Polytropon freebsd at
Wed Feb 19 00:47:50 UTC 2014

On Wed, 19 Feb 2014 00:37:18 +0000, Matthew Seaman wrote:
> On 18/02/2014 22:53, Ronald F. Guilmette wrote:
> > So, um, I've had to put in a new stopgap ipfw rule, just to stop these
> > bloody &^%$#@ NTP reply packets from leaving my server, but what is
> > that Right Way to solve this problem?  I'm guessing that there's
> > something I need to add to my /etc/ntp.conf file in order to tell
> > my local ntpd to simply not accept incoming _query_ packets unlees
> > they are coming from my own LAN, yes?  But obviously, I still need it
> > to accept incoming ntp _reply_ packets or else my machine will never
> > know the correct time.
> > 
> > Sorry.  The answer I'm looking for is undoubtedly listed in an FAQ
> > someplace, but I am very much on edge right at the moment... because
> > I was basiaclly being DDoS'd by all of this stupid NTP traffic... and
> > thus I'm seeking a quick answer.
> Yep.  This is the latest scumbag trick: sending spoofed packets to ntpd
> and using it as an amplifier to do a DDoS against some victim.

For those interested in learning more about how this attack
is being used by scumbags, here are a two links to read:

In this case, CloudFlare has been declared the victim.

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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