blog/Combining_PowerDNS_and_ISC_DHCP_LDAP_objects.html

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   6     <title>Petter Reinholdtsen: Combining PowerDNS and ISC DHCP LDAP objects</title>
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  12  <h1>
  13      <a href="http://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
  14
  15  </h1>
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  20     <div class="entry">
  21       <div class="title">Combining PowerDNS and ISC DHCP LDAP objects</div>
  22       <div class="date">14th July 2010</div>
  23       <div class="body"><p>For a while now, I have wanted to find a way to change the DNS and
  24 DHCP services in Debian Edu to use the same LDAP objects for a given
  25 computer, to avoid the possibility of having a inconsistent state for
  26 a computer in LDAP (as in DHCP but no DNS entry or the other way
  27 around) and make it easier to add computers to LDAP.</p>
  28
  29 <p>I've looked at how powerdns and dhcpd is using LDAP, and using this
  30 information finally found a solution that seem to work.</p>
  31
  32 <p>The old setup required three LDAP objects for a given computer.
  33 One forward DNS entry, one reverse DNS entry and one DHCP entry.  If
  34 we switch powerdns to use its strict LDAP method (ldap-method=strict
  35 in pdns-debian-edu.conf), the forward and reverse DNS entries are
  36 merged into one while making it impossible to transfer the reverse map
  37 to a slave DNS server.</p>
  38
  39 <p>If we also replace the object class used to get the DNS related
  40 attributes to one allowing these attributes to be combined with the
  41 dhcphost object class, we can merge the DNS and DHCP entries into one.
  42 I've written such object class in the dnsdomainaux.schema file (need
  43 proper OIDs, but that is a minor issue), and tested the setup.  It
  44 seem to work.</p>
  45
  46 <p>With this test setup in place, we can get away with one LDAP object
  47 for both DNS and DHCP, and even the LTSP configuration I suggested in
  48 an earlier email.  The combined LDAP object will look something like
  49 this:</p>
  50
  51 <blockquote><pre>
  52   dn: cn=hostname,cn=group1,cn=THINCLIENTS,cn=DHCP Config,dc=skole,dc=skolelinux,dc=no
  53   cn: hostname
  54   objectClass: dhcphost
  55   objectclass: domainrelatedobject
  56   objectclass: dnsdomainaux
  57   associateddomain: hostname.intern
  58   arecord: 10.11.12.13
  59   dhcphwaddress: ethernet 00:00:00:00:00:00
  60   dhcpstatements: fixed-address hostname
  61   ldapconfigsound: Y
  62 </pre></blockquote>
  63
  64 <p>The DNS server uses the associateddomain and arecord entries, while
  65 the DHCP server uses the dhcphwaddress and dhcpstatements entries
  66 before asking DNS to resolve the fixed-adddress.  LTSP will use
  67 dhcphwaddress or associateddomain and the ldapconfig* attributes.</p>
  68
  69 <p>I am not yet sure if I can get the DHCP server to look for its
  70 dhcphost in a different location, to allow us to put the objects
  71 outside the "DHCP Config" subtree, but hope to figure out a way to do
  72 that.  If I can't figure out a way to do that, we can still get rid of
  73 the hosts subtree and move all its content into the DHCP Config tree
  74 (which probably should be renamed to be more related to the new
  75 content.  I suspect cn=dnsdhcp,ou=services or something like that
  76 might be a good place to put it.</p>
  77
  78 <p>If you want to help out with implementing this for Debian Edu,
  79 please contact us on debian-edu@lists.debian.org.</p>
  80 </div>
  81
  82       <div class="tags">Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian">debian</a>, <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/ldap">ldap</a>, <a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug</a>.</div>
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