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Date: Thu, 8 Feb 2001 18:54:49 -0500
From: "Michael H. Warfield" <mhw@wittsend.com>
To: "H. Peter Anvin" <hpa@transmeta.com>
Cc: "Michael H. Warfield" <mhw@wittsend.com>, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org
Subject: Re: DNS goofups galore...
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	"Michael H. Warfield" <mhw@wittsend.com>,
	"H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
In-Reply-To: <95ulrk$aik$1@forge.intermeta.de> <Pine.LNX.4.10.10102081346001.16513-100000@innerfire.net> <95v8am$k6o$1@cesium.transmeta.com> <20010208183232.A1642@alcove.wittsend.com> <3A833005.5C8E0D81@transmeta.com>
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In-Reply-To: <3A833005.5C8E0D81@transmeta.com>; from hpa@transmeta.com on Thu, Feb 08, 2001 at 03:47:17PM -0800
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On Thu, Feb 08, 2001 at 03:47:17PM -0800, H. Peter Anvin wrote:
> "Michael H. Warfield" wrote:
> > 
> > On Thu, Feb 08, 2001 at 02:58:30PM -0800, H. Peter Anvin wrote:
> > > Followup to:  <Pine.LNX.4.10.10102081346001.16513-100000@innerfire.net>
> > > By author:    Gerhard Mack <gmack@innerfire.net>
> > > In newsgroup: linux.dev.kernel
> > > >
> > > > Thanklfully bind 9 barfs if you even try this sort of thing.
> > > >
> > 
> > > Personally I find it puzzling what's wrong with MX -> CNAME at all; it
> > > seems like a useful setup without the pitfalls that either NS -> CNAME
> > > or CNAME -> CNAME can cause (NS -> CNAME can trivially result in
> > > irreducible situations; CNAME -> CNAME would require a link maximum
> > > count which could result in obscure breakage.)
> > 
> >         It generally forces another DNS lookup.  If you do a resolve on
> > a name of type=ANY it returns any MX records and A records.  If you then
> > do a resolve on the MX records, you then get a CNAME and then have to
> > add an additional lookup for the CNAME.  If you have a lot of MX records
> > and not all the servers are "up" that can add up to a significant
> > increase in DNS traffic.
> > 

> Wouldn't that be true for any CNAME anyway?

	That's the point...

	In other words, you do a lookup, you start with a primary lookup
and then possibly a second lookup to resolve an MX or CNAME.  It's only
the MX that points to a CNAME that results in yet another lookup.  An
MX pointing to a CNAME is almost (almost, but not quite) as bad as a
CNAME pointing to a CNAME.

> 	-hpa

> -- 
> <hpa@transmeta.com> at work, <hpa@zytor.com> in private!
> "Unix gives you enough rope to shoot yourself in the foot."
> http://www.zytor.com/~hpa/puzzle.txt

	Mike
-- 
 Michael H. Warfield    |  (770) 985-6132   |  mhw@WittsEnd.com
  (The Mad Wizard)      |  (678) 463-0932   |  http://www.wittsend.com/mhw/
  NIC whois:  MHW9      |  An optimist believes we live in the best of all
 PGP Key: 0xDF1DD471    |  possible worlds.  A pessimist is sure of it!

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