[ntp:questions] better rate limiting against amplification attacks?

David Lord snews at lordynet.org
Thu Jan 16 21:51:43 UTC 2014

Steve Kostecke wrote:
> On 2014-01-16, Greg Troxel <gdt at ir.bbn.com> wrote:
>> Harlan Stenn <stenn at ntp.org> writes:
>>> William Unruh writes:
>>>> I do not mean the default in the config file, I mean the default if
>>>> there is no config file or if nothing is set in the config file.
>>> Then ntpd won't connect to anything and there will be no data to report.
>> This is a ridiculous strawman.   The ntp project is abdicating its
>> responsibility to provide sane default behavior by claiming that no
>> default behavior can make everyone happy and therefore it's not their
>> fault.  The notion that OS packagers somehow have a better idea of usage
>> is also specious.
>> Really, ntpd should, when run with a config file of only
>>   server 0.pool.ntp.org
>>   server 1.pool.ntp.org
>>   server 2.pool.ntp.org
>> behave relatively sanely, including declining to respond to packets that
>> could be amplification attacks,
> The majority use case for ntpd is to synchronize your clock to UTC (i.e.
> a leaf-node client). So an ntpd ought to have the following defaults:
> driftfile /path/to/ntp.drift
> pool pool.ntp.org iburst
> restrict -4 default kod notrap nomodify nopeer noquery
> restrict -6 default kod notrap nomodify nopeer noquery
> restrict
> restrict ::1
> This would enable the majority use case without the need for a
> configuration file.


I have "restrict -4 limited kod nomodify notrap nopeer noquery"

I've not checked most recent docs but thought "limited" was
needed for "kod".

There were also some posts indicating that "kod" could be
counter productive leading to self inflicted DOS.


>> while being usable as a s2/s3 to other nearby nodes.
> Operation as a LAN time server is probably a secondary use case. But the
> defaults listed above would also enable that usage.
>> This notion of good behavior under minimal config seems
>> really obvious to me, yet there is a huge resistance to it, with the
>> notion that every end user should invest the time to be an expert.
> This.

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