<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Brian, you’re welcome. We have had this discussion for maybe more than 10 years but it still surfaces now and then. <div><br></div><div>Glad to see that the root cause is found, now just the solution needs to be implemented.</div><div><br></div><div><br id="lineBreakAtBeginningOfSignature"><div dir="ltr"><pre class="moz-signature" cols="72"><font face=".SFUIDisplay-Regular"><span style="white-space: normal; background-color: rgba(255, 255, 255, 0);">--
Best regards</span></font></pre><pre class="moz-signature" cols="72"><font face=".SFUIDisplay-Regular"><span style="white-space: normal; background-color: rgba(255, 255, 255, 0);">Sten Carlsen</span></font></pre><pre class="moz-signature" cols="72"><font face=".SFUIDisplay-Regular"><span style="white-space: normal; background-color: rgba(255, 255, 255, 0);">No improvements come from shouting:</span></font></pre><pre class="moz-signature" cols="72"><font face=".SFUIDisplay-Regular"><span style="white-space: normal; background-color: rgba(255, 255, 255, 0);">"MALE BOVINE MANURE!!!" </span></font></pre></div><div dir="ltr"><br><blockquote type="cite">On 11 Jul 2024, at 15.19, Cuttler, Brian R (HEALTH) <brian.cuttler@health.ny.gov> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
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<p class="MsoNormal">Sten,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Okay, pretty much what I’d thought, just never actually saw it before.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Reservations don’t protect the IP, the right answer here is to change to limits on the dynamic pool and make sure my reservations are outside of the pool<o:p></o:p></p>
<p class="MsoNormal">I’m actually wondering why I have a reservation for this at all, that would also have resolve the issue, and would have not caused the users an issue as that subnet creates DDNS entries for us.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">An entry like this?<br>
boot.log.2:May 5 08:42:28 cedar dhcpd[863]: Remove host declaration suraj or remove 10.50.148.212<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I don’t routinely scan the dhcp logs, will maybe have to create a job to find such messages and notify me.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Our static entries by and large are non-global, they are within the stanza but that hasn’t been a problem, will look to make updates as time allows.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Joe, Nilesh, without CC’d the list, can you see any reason why we need a reserved IP for Suraj?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Brian<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> dhcp-users <dhcp-users-bounces@lists.isc.org> <b>
On Behalf Of </b>Sten Carlsen<br>
<b>Sent:</b> Thursday, July 11, 2024 6:12 AM<br>
<b>To:</b> Users of ISC DHCP <dhcp-users@lists.isc.org><br>
<b>Subject:</b> Re: two hosts with the same IP<o:p></o:p></p>
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<p class="MsoNormal">I believe there should be a specific warning in the log during startup.<o:p></o:p></p>
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<pre><span style="font-family:".SFUIDisplay-Regular",serif">-- Best regards</span><o:p></o:p></pre>
<pre><span style="font-family:".SFUIDisplay-Regular",serif">Sten Carlsen</span><o:p></o:p></pre>
<pre><span style="font-family:".SFUIDisplay-Regular",serif">No improvements come from shouting:</span><o:p></o:p></pre>
<pre><span style="font-family:".SFUIDisplay-Regular",serif">"MALE BOVINE MANURE!!!" </span><o:p></o:p></pre>
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<p class="MsoNormal" style="margin-bottom:12.0pt">On 11 Jul 2024, at 02.23, Glenn Satchell <<a href="mailto:Glenn.Satchell@uniq.com.au">Glenn.Satchell@uniq.com.au</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">hi Brian,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">fixed-address assignments must be outside the pool of dynamic addresses to prevent this situation.<o:p></o:p></p>
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<p class="MsoNormal">If the fixed-address device is down, then the dynamic pool will see that as free when it does a ping check and happily assign it. then when the fixed-address device requests the ip it will always be assigned.<o:p></o:p></p>
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<p class="MsoNormal">This is mentioned in the docs, dhcpd.conf man page i think.<o:p></o:p></p>
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<p class="MsoNormal">regards,<br>
Glenn<o:p></o:p></p>
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<p class="MsoNormal">On 11 July 2024 6:12 am, "Cuttler, Brian R (HEALTH)" <<a href="mailto:brian.cuttler@health.ny.gov">brian.cuttler@health.ny.gov</a>> wrote:<o:p></o:p></p>
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<p>Running DHCP on Ubuntu 22.04.4 LTS<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>brian@cedar:/var/log$ DHCP -V<o:p></o:p></p>
<p>Internet Systems Consortium DHCP Server 4.4.1<o:p></o:p></p>
<p>Copyright 2004-2018 Internet Systems Consortium.<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Noted one system in particular was having network issues, ping to the IP was good, ping from the IP was problematic, lots of dropping pings in about 25 second groups/blocks.<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Also having trouble maintaining SSH connection into the host, and host keys needed to be removed and reaccepted.<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>On a hunch I checked the dhcp log and found two different MAC addresses receiving the same IP.<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Jul 9 11:49:38 cedar DHCP[1019]: DHCPREQUEST for 10.50.148.212 from d4:5d:64:08:91:7c via 10.50.148.1<o:p></o:p></p>
<p>Jul 9 11:49:38 cedar DHCP[1019]: DHCPACK on 10.50.148.212 to d4:5d:64:08:91:7c via 10.50.148.1<o:p></o:p></p>
<p>Jul 10 15:04:17 cedar DHCP[1019]: DHCPREQUEST for 10.50.148.212 from b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p>Jul 10 15:04:17 cedar DHCP[1019]: DHCPACK on 10.50.148.212 to b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p>Jul 10 15:05:16 cedar DHCP[1019]: DHCPDISCOVER from b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p>Jul 10 15:05:16 cedar DHCP[1019]: DHCPOFFER on 10.50.148.212 to b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p>Jul 10 15:05:16 cedar DHCP[1019]: DHCPREQUEST for 10.50.148.212 (10.50.156.21) from b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p>Jul 10 15:05:16 cedar DHCP[1019]: DHCPACK on 10.50.148.212 to b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>I also note that one of the two hosts has a reservation.<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> host Suraj {<o:p></o:p></p>
<p> hardware ethernet d4:5d:64:08:91:7c;<o:p></o:p></p>
<p> fixed-address 10.50.148.212;<o:p></o:p></p>
<p> }<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>While I realize that a host with a reservation might be down, and another machine could get the IP if its in the available pool I’m very surprised by the behavior we were seeing.<br>
If the non-received MAC received the IP wouldn’t the MAC with the reservation still cause a ping test for availability to be performed?<br>
I can’t think of any other way this could have happened.<o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Can anyone help me to understand what actually happened and how best to prevent similar events in the future?<br>
<br>
thanks in advance,<o:p></o:p></p>
<p>Brian<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> <o:p></o:p></p>
<p><span style="font-size:12.0pt;font-family:"Arial",serif">Brian Cuttler, System and Network Administration</span><o:p></o:p></p>
<p><span style="font-size:12.0pt;font-family:"Arial",serif">Wadsworth Center, NYS Department of Health</span><o:p></o:p></p>
<p><span style="font-size:12.0pt;font-family:"Arial",serif">Albany, NY 12201 POB 509</span><o:p></o:p></p>
<p><span style="font-size:12.0pt;font-family:"Arial",serif"><a href="mailto:Brian.Cuttler@Health.NY.gov"><span style="color:#0563C1">Brian.Cuttler@Health.NY.gov</span></a></span><o:p></o:p></p>
<p><span style="font-size:12.0pt;font-family:"Arial",serif">518 486-1697</span><o:p></o:p></p>
<p> <o:p></o:p></p>
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