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<div class="moz-cite-prefix">On 01/11/2013 07:58 AM, Kyle Johnson
wrote:<br>
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cite="mid:CAK9Qi6VKrAb2Te=t1p2qyZe7Z0zF7JgY1XX3cy+RfSM8U0yaMQ@mail.gmail.com"
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<div>Hello everyone,<br>
<br>
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DHCP isc-dhcpd-4.1.1-P1<br>
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BIND 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6_3.5 <br>
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<div>CentOS 6.3 clients<br>
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<div><br>
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I am having an issue. I am going to step through my
scenario below. Please forgive me if I get a few details
wrong. <br>
<br>
I create a VM with the hostname foobar. DHCP gives it a
lease, and with DDNS, creates the DNS (A, PTR and TXT)
records. This is good. Now I destroy foobar and recreate
him with the same hostname, but put him on a different
network (vlan); foobar's MAC address has obviously changed.<br>
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At this point, after firing foobar back up, he will get a DHCP
lease, but the DNS records will not be updated because the TXT
record (a hash of MAC + hostname?) does not match.<br>
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<div>This seems to be the expected behavior, however it is not
the behavior that I want to see. So now I modify foobar's
dhclient.conf and tell it to send an identifier, like so:<br>
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<div>send dhcp-client-identifier "foobar.domain.tld";<br>
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<div>Next I freeze my forward and reverse zones, manually remove
any offending entries (A, PTR and TXT), thaw the zones, and
then reboot foobar.<br>
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<div>Now his DNS records are created, because there is nothing
to conflict with. This time, the TXT record should match the
client's identifier (his hostname, in this case, as sent in
dhclient.conf).<br>
<br>
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<div>So once again, I shutdown foobar, remove his NIC, add a new
NIC (changing the MAC address), and put him on a different
network. After firing him back up, he gets a DHCP lease on
the correct network, but still his DNS records are not
updated!<br>
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<div>I am imagining that my understanding of DDNS and TXT
records is way wrong.<br>
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<ol>
<li>Are my above assumptions correct?</li>
<li>Is a TXT record, by default, a hash of MAC + hostname?</li>
<li>
If I specify a dhcp-client-identifier in dhclient.conf,
how is the TXT record now created (a hash of just the
hostname now)?</li>
<li>I understand that the above behavior is in place to
prevent clients from assuming the hostname of existing
clients. In most environments, this is fine, but in mine,
I have enough control over my network to consider that
possibility moot.<br>
</li>
<li>Can I achieve my desired results? I am working in a
very dynamic environment and do not want to manually
freeze and thaw zones every I need to move a host.</li>
<li>I did not post any log output as I don't think it is
needed at this point. If it is, please ask, and I will
provide.<br>
</li>
</ol>
<p>Thank you for your time!</p>
<p>Kyle Johnson<br>
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</blockquote>
<br>
<span style="font-family: "Courier New";">You need to set
'update-conflict-detection false' which will allow dhcpd to over
write the A/PTR/TXT when the TXT hash doesn't match or is
non-existent (as when windows clients self update). For multiple
NIC hosts under the same host name (wired/wireless) this will also
allow the entry to have the most recent assigned address or
updated address if you have update optimization set to false as
well. </span><br>
<br>
<pre class="moz-signature" cols="72">--
-James</pre>
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