<div dir='auto'><div dir="auto"><div>hi Brian,</div><div dir="auto"><br></div><div dir="auto">fixed-address assignments must be outside the pool of dynamic addresses to prevent this situation.</div><div dir="auto"><br></div><div dir="auto">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.</div><div><br></div><div dir="auto">This is mentioned in the docs, dhcpd.conf man page i think.</div><div dir="auto"><br></div><div data-smartmail="gmail_signature">regards,<br>Glenn</div></div><div><br><div class="elided-text">On 11 July 2024 6:12 am, "Cuttler, Brian R (HEALTH)" <brian.cuttler@health.ny.gov> wrote:<br type="attribution"><blockquote style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">
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<p>Running DHCP on Ubuntu 22.04.4 LTS</p>
<p> </p>
<p>brian@cedar:/var/log$ DHCP -V</p>
<p>Internet Systems Consortium DHCP Server 4.4.1</p>
<p>Copyright 2004-2018 Internet Systems Consortium.</p>
<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.</p>
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<p>Also having trouble maintaining SSH connection into the host, and host keys needed to be removed and reaccepted.</p>
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<p>On a hunch I checked the dhcp log and found two different MAC addresses receiving the same IP.</p>
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<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</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</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</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</p>
<p>Jul 10 15:05:16 cedar DHCP[1019]: DHCPDISCOVER from b0:7b:25:de:57:84 (berkeley) via 10.50.148.1</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</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</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</p>
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<p>I also note that one of the two hosts has a reservation.</p>
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<p> host Suraj {<!-- --></p>
<p> hardware ethernet d4:5d:64:08:91:7c;</p>
<p> fixed-address 10.50.148.212;</p>
<p> }</p>
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<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.</p>
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<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,</p>
<p>Brian</p>
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<p><span style="font-size:12pt;font-family:'arial' , serif">Brian Cuttler, System and Network Administration</span></p>
<p><span style="font-size:12pt;font-family:'arial' , serif">Wadsworth Center, NYS Department of Health</span></p>
<p><span style="font-size:12pt;font-family:'arial' , serif">Albany, NY 12201 POB 509</span></p>
<p><span style="font-size:12pt;font-family:'arial' , serif"><a href="mailto:Brian.Cuttler@Health.NY.gov"><span style="color:#0563c1">Brian.Cuttler@Health.NY.gov</span></a></span></p>
<p><span style="font-size:12pt;font-family:'arial' , serif">518 486-1697</span><span style="font-size:12pt;font-family:'arial nova' , sans-serif"></span></p>
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