Last Call Review of draft-ietf-dnsop-dns-tcp-requirements-12
review-ietf-dnsop-dns-tcp-requirements-12-tsvart-lc-kuehlewind-2021-08-25-00

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Thanks for the well-written document! I have a couple of points below regarding
the recommend TCP tuning in section 4. Other parts of the document don't seem
to have any transport issues and are clear to me.

First a minor comment here:
"TCP connection timeout, which is often around 60-120 seconds."
I guess this value relates to an RTO of 1s and 6 SYN retries which is the
default in Linux. Maybe say that...? I also recommend to add a link to RFC6298.

And a more general comment on section 4.2: this section takes about various
limits but doesn't recommend any values. I understand that there is not a
one-fits-all solution here but not knowing how to set these values correctly
might scared people aways from supporting TCP. So I think having a discussion
either of default values or how to derives these values based on a certain
configuration would be a very valuable contribution in this document.

Similarly section 4.3 talks about tuning net.ipv4.tcp_fin_timeout, however, it
doesn't provide any guidance on how to tune it; Linux recommend a value of
15-30 seconds. Also setting net.ipv4.tcp_fin_timeout to a too low value and
net.ipv4.tcp_tw_reuse to 1 can cause trouble and should not be done for the
general case. So I don't think that guidance is appropriate without further
discussion of the risks. Please reconsider this part of the document!

On section 4.4, maybe mention TCP fast open here again as well?