Parent is a CNAME
Sam.Wilson at ed.ac.uk
Wed Dec 2 17:52:02 UTC 2009
In article <mailman.1165.1259775639.14796.bind-users at lists.isc.org>,
Joseph S D Yao <jsdy at tux.org> wrote:
> On Wed, Dec 02, 2009 at 12:47:08PM +0000, Sam Wilson wrote:
> > In article <mailman.1153.1259725836.14796.bind-users at lists.isc.org>,
> > Joseph S D Yao <jsdy at tux.org> wrote:
> > > No.
> > Not true. CNAME chains - CNAMEs pointing to other CNAMEs - are
> > inefficient and discouraged but the DNS spec is built to ensure that
> > they work. Check out www.google.com sometime (or www.google.co.uk) and
> > wonder at how many people would be annoyed if they didn't.
> CNAME chains have nothing to do with this. THIS is perfectly legal:
> a CNAME b
> b CNAME c
> c CNAME d
> d CNAME extra-ordinary
> although, as mentioned, inefficient.
My bad - I read your initial statement as banning names with CNAME
records from the RHS of other RRs, not from the LHS, and I was offering
> THIS is not legal:
> a CNAME b
> a CNAME c
> a A 220.127.116.11
To be pedantic, the first alone is legal, but once that exists neither
of the second nor third is legal.
> > > Why not do this?
> > >
> > > subdomain.b A 18.104.22.168
> > > subdomain.b NS ns1.subdomain.b
> > > ns1.subdomain.b A 22.214.171.124
> > If b was itself delegated the CNAME would be problematical again.
> And if all the name servers crashed, then the domain would be unserved.
> Why introduce unnecessary hypotheticals? ;-)
Because you introduced a delegation for a and I wanted to head off the
idea that you could delegate b and then point a to it as a CNAME. You'd
need to use DNAME in that situation.
> And, as pointed out in another post, the CNAME does not appear to be
> problematic in this case, even were it to exist.
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