Common operational misconceptions

Thu Feb 16 12:01:43 UTC 2012

> If you want to know if your resolver talks IPv6 to the world and
> supports 4096 EDNS UDP messages the following query will tell you.
> 
> 		dig edns-v6-ok.isc.org txt
> 
> Similarly for IPv4.
> 
> 		dig edns-v4-ok.isc.org txt

Both PowerDNS recursor 3.3 and Nominum CNS 3.0.5 have problems
with these queries. They both get the TC answer from 149.20.64.58 /
2001:4f8:0:2::8. Then:

- CNS tries with 4000 EDNS UDP size (4000 is the CNS documented max
UDP size), gets another TC.

- PowerDNS doesn't try to used EDNS at all.

Then they both try TCP and get a RST. And then they return SERVFAIL.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no