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<p>Thanks for your reply.</p>
<p>What I found si that you don't need any of those three options -
option host-name caused problems, option dhcp.host-name didn't
help but with option fqdn.hostname it seemed to work, but then I
read man pages for dhcp-options and they say:</p>
<p><tt>option fqdn.hostname --never set--;</tt><tt><br>
</tt><tt><br>
</tt><tt> This option should never be set, but it can be
read back using the option and config-option operators in an
expression, in which case it returns</tt><tt><br>
</tt><tt> the first label in the fqdn.fqdn suboption - for
example, if the value of fqdn.fqdn is "foo.example.com.", then
fqdn.hostname will be "foo".</tt></p>
so I tried it without and everything seems to work (DDNS update
included). So now I just have <br>
<br>
<tt> set mac_6 = suffix(concat("0", binary-to-ascii(16, 8,
"", substring(hardware, 6, 1))), 2);</tt><tt><br>
</tt><tt> ddns-hostname = concat("vm1", mac_6);<br>
</tt><br>
I don't know if it's correct so would appreciate any insight.<br>
<br>
But I have another issue, which I initially thought is related to
this, so would appreciate any halp there too -
<a class="moz-txt-link-freetext" href="https://lists.isc.org/pipermail/dhcp-users/2017-June/020656.html">https://lists.isc.org/pipermail/dhcp-users/2017-June/020656.html</a>.<br>
<br>
Thanks again, Rado.<br>
<br>
<br>
<div class="moz-cite-prefix">On 06/23/2017 04:23 PM, Bill Shirley
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:32000ed4-760e-34ff-61f3-adda9725197d@c3po.polymerindustries.biz">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
I have a some devices that don't provide a hostname. Dynamic DNS<br>
doesn't get updated without a hostname. I use:<br>
<font color="#993300"><tt>#
------------------------------------------------------------------------------</tt><tt><br>
</tt><tt>class "NoName" {</tt><tt><br>
</tt><tt> match if not (</tt><tt><br>
</tt><tt> exists server.ddns-hostname</tt><tt><br>
</tt><tt> or exists fqdn.hostname</tt><tt><br>
</tt><tt> or exists host-name</tt><tt><br>
</tt><tt> );</tt><tt><br>
</tt><tt><br>
</tt><tt> ddns-hostname = concat("NoName-",
binary-to-ascii(16, 8, "", substring(hardware, 4, 3)));</tt><tt><br>
</tt><tt> option dhcp.host-name = config-option
server.ddns-hostname;</tt><tt><br>
</tt><tt># option fqdn.hostname = config-option
server.ddns-hostname;<br>
}</tt><tt><br>
</tt><tt>#
------------------------------------------------------------------------------</tt><tt><br>
</tt></font>to create a hostname for them. It uses the last 3
bytes of the MAC address<br>
as part of the host name. Note: I'm using '<font color="#993300">option
dhcp.host-name</font>' instead<br>
of '<font color="#993300">option host-name</font>'. I really
don't know if that matters. You might also<br>
try '<font color="#993300">option fqdn.hostname</font>'.<br>
<br>
You can even confine them to a pool:<br>
<font color="#993300"><tt> pool {</tt><tt><br>
</tt><tt> deny dynamic bootp clients;</tt><tt><br>
</tt><tt> allow members of "NoName"; </tt><tt><br>
</tt><tt>.</tt><tt><br>
</tt><tt>.</tt><tt><br>
</tt><tt> }</tt></font><br>
<br>
HTH,<br>
Bill<br>
<br>
<div class="moz-cite-prefix">On 6/23/2017 7:28 AM, Radoslav Pešek
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:b8af0147-6fc1-fef5-cb9d-f061a7a27db2@stuba.sk">
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charset=utf-8">
<p> </p>
<div class="moz-text-html" lang="x-unicode">
<div class="post-text" itemprop="text">
<p>Hi all, <br>
</p>
<p>I sent this email few weeks ago (without being subscribed
here), and didn't receive any reply, nor do I see it in
lists archive. So I write once again after subscription,
hope it will work now.<br>
</p>
<p>~~~~<br>
</p>
<p>My isc dhcp server behaves strangely - it sends some
clients dhcp hostname option value which I don't know
where it is getting it from.</p>
<p>It's on Debian 8.5, version 4.3.1. It's in failover mode.</p>
<p>I'm using dynamic hostname generation for some clients
based on last byte of their mac address:</p>
<pre><code>set mac_6 = suffix(concat("0", binary-to-ascii(16, 8, "", substring(hardware, 6, 1))), 2);
ddns-hostname = concat("vm1", mac_6);
option host-name = config-option server.ddns-hostname;
</code></pre>
<p>So for example client with mac address ending 02 should
get hostname vm102 - and it seems to work correctly - I
added logging to my dhcp config and I see in log file both
option host-name and config-option server.ddns-hostname
set to vm102. </p>
<p>I also see in dhcpd.leases </p>
<pre><code>set mac_6 = "02";
client-hostname "vm102";
</code></pre>
<p>But when I run tcpdump for this client, I see</p>
<p><code>Hostname Option 12, length 5: "vm121" </code></p>
<p>and at least once it changed to vm103.</p>
<p>So where is it getting it from? What are the sources for
this option when dhcp server sends DHCPOFFER or DHCPACK?</p>
<p>It works after dhcp server restart, but then it starts
again after a whlie.</p>
<p>I tried to read isc-dhcp-server's source code but got bit
lost as it was hard to follow.</p>
<p>Thanks for any help.</p>
<p>Rado.</p>
<p><br>
</p>
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