TWC (AS11351) blocking all NTP?

Matthew Petach mpetach at
Sun Feb 2 22:49:49 UTC 2014

On Sun, Feb 2, 2014 at 2:17 PM, Cb B <cb.list6 at> wrote:

> On Feb 2, 2014 8:35 AM, "Jonathan Towne" <jtowne at> wrote:
> >
> > The provider has kindly acknowledged that there is an issue, and are
> > working on a resolution.  Heads up, it may be more than just my region.
> >
> And not just your provider, everyone is dealing with UDP amp attacks.
> These UDP based amp attacks are off the charts. Wholesale blocking of
> traffic at the protocol level to mitigate 10s to 100s of gigs of ddos
> traffic is not "knee jerk", it is the right thing to do in a world where
> bcp 38 is far from universal and open dns servers, ntp, chargen, and
> whatever udp 172 is run wild.
> People who run networks know what it takes to restore service. And
> increasingly, that will be clamping ipv4 UDP in the plumbing,  both
> reactively and proactively.

Please note that it's not that UDP is at fault here; it's
applications that are structured to respond to small
input packets with large responses.

If NTP responded to a single query with a single
equivalently sized response, its effectiveness as
a DDoS attack would be zero; with zero amplification,
the volume of attack traffic would be exactly equivalent
to the volume of spoofed traffic the originator could
send out in the first place.

I agree the source obfuscation aspect of UDP can be
annoying, from the spoofing perspective, but that
really needs to be recognized to be separate from
the volume amplification aspect, which is an application
level issue, not a protocol level issue.


PS--yes, I know it would completely change the
dynamics of the internet as we know it today to
shift to a 1:1 correspondence between input
requests and output replies...but it *would*
have a nice side effect of balancing out traffic
ratios in many places, altering the settlement
landscape in the process.  ;)

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