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Date: Fri, 29 Nov 2013 22:59:13 -0500
From: Rich Felker <>
Subject: Re: IPv4 and IPv6 addresses in resolv.conf

On Fri, Nov 29, 2013 at 10:51:16PM -0500, Rich Felker wrote:
> On Fri, Nov 29, 2013 at 10:45:26PM -0500, Strake wrote:
> > On 29/11/2013, Rich Felker <> wrote:
> > > But that would mean complete unconditional DNS failure on systems
> > > lacking IPv6.
> > 
> > We could do so iff system has IPv6. Switching on whether system has
> > IPv6 rather than whether resolv.conf has any IPv6 nameservers means
> > * no check whether resolv.conf includes v6 server
> > * that adding a v6 server to resolv.conf can not break DNS even on
> > systems lacking v6
> > which seems saner.
> OK, so how do we detect if the system "has IPv6"? I don't think it's

BTW, short of an answer to this question, I think the approach I
already suggested is rather safe. I can't imagine how an IPv6
nameserver address would end up in resolv.conf on a system completely
lacking IPv6 support at the kernel level.


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