[Pdns-users] Slow query and SERVERFAIL from local pdns_recursor

Thomas Mieslinger miesi at mail.com
Fri Sep 11 07:25:13 UTC 2020

On 9/10/20 3:40 PM, Christian Degenkolb wrote:
> what is a reasonable low value for udp-truncation-threshold? I tried
> with 900 and 600 (as low as half the default value) but found no
> improvements.

I use 1220 because the always recommended 1232 does not work for me with

Some months ago the network team forgot to configure fragment handling
correctly on JunOS. As soon as I lowered the udp-truncation-threshold
dhl.com and others started working immediately.

> Also I don't think this is a vmware.com problem since I have the same
> problem with multiple domains.

Another thing that I noticed is that not well utilized recursors perform
bad because they need to work through the whole chain from . to the
zones nameserver including many extra queries for dnssec.

"not well utilized" as in less than 10k queries/second.

Please try to "preheat" your recursor and see what changes. For use at
home I've written https://github.com/miesi/DNS-Standheizung to have all
tld namesserver with their A/AAAA/... in the recursors chache



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