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SubjectRe: DNS goofups galore...
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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