[NLNOG] What =?utf-8?Q?if=E2=80=A6_?=DNS over TCP?

Thomas de Looff - PCextreme thomas at pcextreme.nl
Fri Feb 9 16:16:55 CET 2018

Hi Mark and Benno,

On 7 February 2018 at 17:16:11, Mark Schouten (mark at tuxis.nl) wrote:
> Hi Benno,
> On woensdag 7 februari 2018 16:53:55 CET Benno Overeinder wrote:
> > Question 1: Was the recent DDOS armed by open resolvers allowing for a
> > DNS amplification attack? I didn't heard about the specifics other than
> > a botnet, hired for a nominal fee.
> I don't know.

The recent DDoS attacks that I see are mainly synflood attacks. Relatively small in Gbit/s.
UDP attacks are not that popular anymore in comparison with 2016.
We received over 100 DDoS attacks last month, between 2 - 40 Gbit/s.

> > Question 2: Are DNS amplification attacks still an issue? As far as I
> > understand are most name servers equipped with RRL (response rate
> > limiting), effectively nullifying (well almost) the spoofed traffic
> > reflection.
> IMHO RRL is a workaround (which might be pretty effective, but still), not a
> solution. And correctly configured nameserver probably aren't a big issue
> whatsoever. But, by depending on DNS over UDP, we cannot just filter it and let
> people that misconfigure their servers be the victim of their own fault.
> > I guess most DNS name servers (authoritative/recursive) do support TCP
> > to deal with TC bit (truncated answer) and (should try) TCP fallback.
> > Measuring name server TCP capabilities by scanning name servers might be
> > quite an effort (i.e. which name server to scan?), but you can also look
> > at the different DNS server implementations, e.g. BIND, PowerDNS, Knot
> > DNS and NSD/Unbound. ;-)
> I'm scanning as we speak. The script I wrote (which probably contain a few
> bugs, but gives some insight) has scanned 8240 nameservers so far, 495 of
> which did not respond to TCP. Input is a version of the alexa top 1 million
> and a dump of my resolvercaches, of which the nameservers are looked up and
> checked. Newly discovered domains get added to the queue in the process.
> > In the past years, we (the open source DNS community) made substantial
> > progress with introducing DNS-over-TLS in the different code bases.
> > This started in the IETF DPRIVE working group and implementations are
> > well on the way. See for more information https://dnsprivacy.org/wiki/.
> >
> > All this DNS-over-TLS work focuses on stub to resolver interactions: the
> > easy part wrt scaling (up to 10.000 clients). The hard part is still
> > the authoritatives that see up to millions queries per second.
> DNS-over-TLS specifically focus on client-resolver communication. Which is
> nice, but still doesn't allow me to just filter UDP/53 on my edges.
> Possibly handling millions of queries over TCP is hard (not an expert on
> that), but I guess we have other services handing lots of requests as well,
> don't we?
> --
> Kerio Operator in de Cloud? https://www.kerioindecloud.nl/
> Mark Schouten | Tuxis Internet Engineering
> KvK: 61527076 | http://www.tuxis.nl/
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Thomas de Looff 

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