[Unbound-users] Disabling EDNS0?

Jelte Jansen jelte.jansen at sidn.nl
Wed Oct 15 08:48:22 UTC 2014

On 10/14/2014 09:13 PM, Michael Tokarev wrote:
> Hello.
> It looks like a there's a common problem in various networks, -- some
> resolvers does not understand EDNS0 OPT record at the end of the DNS
> query packet and returns either NXDOMAIN or NODATA response to *any*
> such query, no matter if the domain in question exists or not.

I guess you mean authoritative servers, not resolvers?

> After facing this prob multiple times, I finally tried to configure
> unbound (1.4.22) to stop using EDNS0 in the first place.  But it looks
> like there's no way to turn it off, as far as I can see at least.
> I only found edns-buffer-size setting, and it works, by changing
> adverticing buffer size in the OPT record.  Yes, I can set it to
> 512 just fine, and unbound will happily add the corresponding OPT
> record.
> But the question is how to stop it from _adding_ this record in
> the first place?

Not sure if there is such an option, but I kind of hope there isn't;
you'd be getting yourself stuck in compatibility with broken
authoritative servers (because they sure are broken if they respond with
NXDOMAIN or NODATA because of EDNS0), and in the long run this isn't a
good approach. No large DNS packets, no DNSSEC (at all!), etc.

BTW, if you are looking for a way to disable EDNS0, you should disable
it *only* for those domains (or nameservers). Not sure if that is
possible either :)

But I'd rather see we try to get those broken domains fixed. Note that
they do not need to support EDNS0, they just need to follow the RFCs
instead of giving false answers.

Note that any reasonably modern resolver would be adding EDNS0 by
default, so if they are responding badly to it they should have a lot
more problems.


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