On Fri, Mar 20, 2020 at 7:16 AM Ralf Weber <[email protected]> wrote:

> Moin!
>
> If the hardware and the location of the client and server are
> identical it is impossible to get more throughput, better latency using
> DoT or DoH, then DNS over UDP/53 given two similar written servers.
>

Hi Ralf,

A trivial example in which this is not true is in the case where one or
more routers in the network path maintain different queues for UDP and TCP
traffic.  When this is the case, a robust queue for TCP and a meager one
for UDP can easily mean that the end-to-end performance for the client is
better for DoT (or DNS over TCP/53), simply because the loss on the UDP
path is high.  This is especially true if you measure over a flight of
queries (say, all the DNS queries a web page needs to resolve) and DoT
keeps an open session for the whole flight.  To put this another way,
if what you are measuring is the DNS component of page load time,  DNS
timeouts for the lost UDP packets  in a queue-starved path can kill the
performance.

As Eric points out, we have to be careful to describe what we're measuring
here, and there are definitely different views of what we're optimizing
for.

regards,

Ted Hardie



> —--
> Ralf Weber
>
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