Why DNSSEC errors for bund.de?

[Chris Thompson]

On May 24 2011, I wrote:

>We are getting DNSSEC-related SERVFAILs on names in bund.de (e.g.
>mx1.bind.de). This happens with all of BIND 9.7.3-P1, 9.7.4b1 and
>9.8.0-P1 configured with the root and dlv.isc.org trust anchors.
>
>However, I can't see what is actually wrong with it, using dig +cd as
>necessary. All the signatures appear to have valid start/stop times, and
>http://dnsviz.net/d/mx1.bund.de/dnssec/ seems pretty happy with it. There
>are a lot of false trails (e.g. the DS records for it in "de") but that
>shouldn't stop BIND finding the one that works (DLV in dlv.isc.org ->
>KSK with tag 10923 -> ZSK with tag 4814), should it?
>
>It may be significant that this problem was reported to us on the same
>day that obscured DNSKEY records were introduced into the "de" zone...

That seems almost certain to be the precipitating event, in fact.
I can produce the same effect for all 31 zones that are both registered
in dlv.isc.org *and* have a DS record in dlv.isc.org:

  adns1.de.                           ralf-pulz.de.
  brj-berlin.de.                      reichel-jens.de.
  btw-kinderdorf.de.                  schrimpe.de.
  buergerhaushalt-marzahn.de.         sgfun.de.
  bund.de.                            sgmail.de.
  com.de.                             stadtteilzeitung-nordwest.de.
  exanames.de.                        stefan-gransow.de.
  gun.de.                             stegranet.de.
  idkom-networks.de.                  steinmuss.de.
  ifw-dresden.de.                     unixbuero.de.
  iks-jena.de.                        verein-kiekin.de.
  ipse-online.de.                     wartenbergerhof.de.
  judo-dresden.de.                    wikileaks.de.
  ombudschaft.de.                     zrb-kiekin.de.
  ombudschaft-jugendhilfe.de.

Among other oddities:

  dig +dnssec dnskey [zone] gives the right answer *without* the ad bit
  dig +dnssec soa [zone] gives SERVFAIL, unless +cd is used as well.

-- 
Chris Thompson
Email: cet1 at cam.ac.uk