[dns-operations] Questions on DNS Flag day 2020 proposal

Tony Finch dot at dotat.at
Mon Jun 17 11:05:17 UTC 2019

Paul Vixie <paul at redbarn.org> wrote:
> the position i heard was, we know how to do tcp at scale, look at any
> modern web server or load balancer -- so, just do what they do. i didn't
> agree that we know how to do tcp at scale, or that web servers or load
> balancers are good examples. however, that seems to have been consensus.
> noting, such a web server can require tens of gigabytes of kernel memory
> to hold all of the necessary connection state. not a design worthy of
> emulation, according to me.

This is a nice description of the discussion, but I think what's going on
is people yelling at each other across a canyon (yelling in a reasonably
friendly manner, I think).

There are two break points in "at scale" here: DNS servers have
historically been (and often still are) terrible at handling TCP. This is
an entirely userland problem, and there is a lot of scope (orders of
magnitude) for DNS servers being less terrible by doing what web servers

The other break point is the whole-system performance differences due to
the extra state that TCP requires compared to UDP. This should not be
ignored, even though that kind of performance problem is a long way out of
reach for many systems :-)

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
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4 later. Slight or moderate, becoming smooth or slight later. Occasional rain
or drizzle in south. Good, occasionally moderate in south.

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