Re: [Ntp] Antw: Re: Antw: [EXT] Re: WGLC on draft‑ietf‑alternative‑port‑01

Miroslav Lichvar <mlichvar@redhat.com> Mon, 02 August 2021 07:37 UTC

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Date: Mon, 2 Aug 2021 09:37:36 +0200
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
Cc: halmurray+ietf@sonic.net, "ntp@ietf.org" <ntp@ietf.org>
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On Mon, Aug 02, 2021 at 08:02:16AM +0200, Ulrich Windl wrote:
> I just wonder: Wouldn't rate limiting (or bandwidth limiting) be the correct
> way to do?

I think that's what they currently do. It effectively causes a DoS on
NTP. See the discussions at community.ntppool.org. Large numbers of
servers are randomly rejected from the pool due to heavy packet loss
specific to port 123 on the path to the monitoring system.

> I don't consider the smart solution to be smart actually.
> Maybe even considering the input/output (request/response) ratio would be even
> better.

That would require tracking each address separately. Good luck doing
that at the network speeds the ISPs work with.

A more practical solution would be to specifically drop only NTP mode
6/7 packets, but even this functionality is missing in (most of?) the
hardware.

-- 
Miroslav Lichvar