[dns-operations] DNSviz and G-root: EDNS issue?

Stephane Bortzmeyer bortzmeyer at nic.fr
Wed Oct 13 07:07:14 UTC 2021


On Tue, Oct 12, 2021 at 01:01:08PM -0400,
 Matthew Pounsett <matt at conundrum.com> wrote 
 a message of 11 lines which said:

> > This might be a known intermittent IPv6 routing issue with DNSviz, do
> > you see this problem for v4 and/or v6 ?
> 
> That would show up as a non-answer over IPv6, rather than an apparent
> PMTU/EDNS problem.

DNSviz (and similar tools) may wrongly diagnose a PMTU problem if
there are random losses.

1) Try with bufsize=4096. No answer, because of a random packet loss.
2) Retry with bufsize=1024. Answer received, therefore it must be a
   PMTU problem.


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