FORMERR responses after upgrading resolver from 9.16 to 9.18.8

[Mark Andrews]

> On 20 Oct 2022, at 22:49, Andreas S. Kerber <ask at ag-trek.de> wrote:
> 
> Am Thu, Oct 20, 2022 at 01:23:47PM +0200 schrieb Ondřej Surý:
>> did you try writing to elbrev.com <http://elbrev.com/> operators to fix their servers to stop breaking DNS protocol? It often helps. (I'm ccing the contact in their SOA records, so let's see if anything happens.)
>> 
>> It's not lack of EDNS0 support, but they fail to properly process unknown EDNS0 options - DNS Cookie in this specific example:
> 
> Hi Ondřej,
> 
> thanks for your quick reply and analysis regarding DNS cookies.
> Is there maybe an option to configure 9.18 to act as if it was 9.16 in this regard?
> Honestly I haven't contacted the elbrev.com people (see below).
> 
> 
>>> Of course I would prefer to upgrade back to 9.18.X, but I guess I won't be able to find all EDNS0 incompatible servers and loosing customers to 8.8.8.8 - which is able to resolve these names..
>> This is kind of moot argument - the DNS needs to evolve, and it can't evolve if we keep supporting broken stuff. This needs to be fixed on the authoritative operator side, not in BIND 9.
> 
> You're absolutely right. I guess I've just kind of given up on convincing other people the fix their stuff (dayjob trauma). Sorry about that.

It’s also a very small percentage of servers that are broken.  If you look at the time series
on https://ednscomp.isc.org/ you can drill done and see the values.  For example there are a
little over 10 servers for all zones in .GOV that exhibit this broken behaviour.  It’s gone
from ~11% in 2014 to 0.26% currently.  We are at the mop up stage.  For some other populations
we are at 0%.

The EDNS specification was updated in April 2013 to specify some unspecified behaviour.  In
particular this was added.

   Any OPTION-CODE values not understood by a responder or requestor
   MUST be ignored.  Specifications of such options might wish to
   include some kind of signaled acknowledgement.  For example, an
   option specification might say that if a responder sees and supports
   option XYZ, it MUST include option XYZ in its response.


Mark
-- 
Mark Andrews, ISC
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PHONE: +61 2 9871 4742              INTERNET: marka at isc.org