Re: [dane] An AD bit discussion

Viktor Dukhovni <viktor1dane@dukhovni.org> Wed, 26 February 2014 17:36 UTC

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Date: Wed, 26 Feb 2014 17:36:30 +0000
From: Viktor Dukhovni <viktor1dane@dukhovni.org>
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Subject: Re: [dane] An AD bit discussion
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On Wed, Feb 26, 2014 at 05:24:37PM +0000, Tony Finch wrote:

> > A) strip the AD bit in struct addrinfo for "untrusted nameservers". A new
> >    configuration mechanism will allow white-listing nameservers and 127.0.0.1
> >    will always be on the whitelist.
> 
> That sounds like a fair plan.

It is in fact problematic if both 127.0.0.1 and another nameserver
are listed.  The correct semantics of that are hard to define.  It
makes more sense to define a boolean primitive that marks all the
nameservers collectively as either trusted or not.

> Question: along with this change are you planning to change the resolver
> to set the AD flag in queries when the nameserver is known to be safe?
>
> Usually the AD flag only appears in responses if the query had the AD or
> DO flags set. DO is a bit wasteful for clients that only care about the AD
> bit. However the only DNSSEC switch that libc resolvers currently have is
> options edns0 (which implies DO).

The RES_USE_DNSSEC flag turns on the "DO" bit.  I would be surprised
if RES_USE_EDNS0 enabled "DO".  As for setting the "AD" bit in the
request automatically, it probably should still require an explicit
indication of interest from the application or be set via a default
option value /etc/resolv.conf.

-- 
	Viktor.