[Pdns-users] EDNS support + default buffer size

Michael Fincham michael at unleash.co.nz
Thu Mar 18 02:48:48 UTC 2010

Hi all,

I've just tested the PowerDNS Recursor 3.2 with its out of the box
configuration against the tests outlined at

It seems that EDNS is disabled by default, which is confirmed by the
comment attached to changeset #1430

Looking at the source it seems in 3.2 an option "disable-edns=no" was
added which turns EDNS support on. A cursory test here shows that adding
this to the stock config does cause the dns-oarc reply size test to
report a reply size of 1200 vs 512 when EDNS is off.

What is the status of EDNS support? Is it safe to rely on in production
environments? What specifically does the "nothing but trouble" comment
on the changeset refer to?

Also, the buffer size of "1200" appears to be hard coded. Is there any
particular reason for this value? I'm guessing it has to do with
avoiding fragmentation, but it'd be nice to know for sure.

-Michael Fincham
System Administrator, Unleash
Phone: 0800 750 250

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