<div dir="ltr"><div>We are currently moving some of our DNS infrastructure, and we would like to test it in one scope before we deploy globally and I am running in to a somewhat unusual problem. Running ISC DHCP on Ubuntu 12.04 LTS, it seems that whenever a client is sending a DHCPINFORM, the DHCP daemon responds with options that are set globally, rather than the options set in the appropriate scope.</div>
<div><br></div><div style>The DHCP configuration file:</div><div style><br></div><div style>--- begin config file ---</div><div style><div>ddns-update-style none;</div><div><br></div><div>option domain-name "test.internal";</div>
<div>option domain-name-servers 10.80.1.2, 10.80.2.3;</div><div><br></div><div>default-lease-time 86400;</div><div>max-lease-time 86400;</div><div><br></div><div>authoritative;</div><div><br></div><div>log-facility local7;</div>
<div><br></div><div>subnet 10.80.0.0 netmask 255.255.0.0 {</div><div> pool {</div><div> range 10.80.10.0 10.80.11.255;</div><div> option subnet-mask 255.255.0.0;</div><div> option routers 10.80.1.1;</div>
<div> option domain-name-servers 10.3.12.100, 10.3.12.121;</div><div> }</div><div>}</div><div style>--- end config file ---</div><div><br></div><div style>When a client on the <a href="http://10.80.0.0/16">10.80.0.0/16</a> subnet does a normal release/discover/offer/request/ack, it is given the correct nameserver info (10.3.12.100 and 10.3.12.121). However, when that same client does an inform/ack, he is given nameservers 10.80.1.2 and 10.80.2.3. In my understanding, scope should always override global, but that doesn't seem to be the case here.<br>
</div><div style><br></div><div style>We have a workaround, which is not defining any global DNS servers and specifying the correct ones for each scope, but after having spent a few days on troubleshooting the issue, I want to find out WHY this is happening. Are we missing something obvious (or even something obscure?)</div>
</div><div><br></div><div>Interesting side-note: After finding 48 offending packets in a packet trace of over 1 million, I am now at a point where I can fairly confidently state that the only time my clients are sending DHCPINFORM is when they are actively running a Windows Update cycle on Windows 7, or if after having applied updates, they have not yet rebooted. While that gives us an interesting metric as to who has not yet rebooted after applying updates, it is not what I'm looking for at this time ;-)</div>
<div><br></div><div style>I look forward to any responses,</div><div style><br></div><div>-Kees</div><div><br clear="all"><div><div><em>Dr. Kees Leune</em></div><div>Information Security Officer</div><div>Adelphi University<br>
Garden City, NY<br><br></div></div>
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