Re: two hosts with the same IP
Sten Carlsen <[email protected]> Thu, 11 Jul 2024 23:31:02 +0200
| Newsgroups | gmane.network.dhcp.isc.dhcp-server |
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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charset=3D=
utf-8"></head><body dir=3D"auto">Brian, you=E2=80=99re welcome. We have had t=
his discussion for maybe more than 10 years but it still surfaces now and th=
en. <div><br></div><div>Glad to see that the root cause is found, now j=
ust the solution needs to be implemented.</div><div><br></div><div><br id=3D=
"lineBreakAtBeginningOfSignature"><div dir=3D"ltr"><pre class=3D"moz-signatu=
re" cols=3D"72"><font face=3D".SFUIDisplay-Regular"><span style=3D"white-spa=
ce: normal; background-color: rgba(255, 255, 255, 0);">--=20
Best regards</span></font></pre><pre class=3D"moz-signature" cols=3D"72"><fo=
nt face=3D".SFUIDisplay-Regular"><span style=3D"white-space: normal; backgro=
und-color: rgba(255, 255, 255, 0);">Sten Carlsen</span></font></pre><pre cla=
ss=3D"moz-signature" cols=3D"72"><font face=3D".SFUIDisplay-Regular"><span s=
tyle=3D"white-space: normal; background-color: rgba(255, 255, 255, 0);">No i=
mprovements come from shouting:</span></font></pre><pre class=3D"moz-signatu=
re" cols=3D"72"><font face=3D".SFUIDisplay-Regular"><span style=3D"white-spa=
ce: normal; background-color: rgba(255, 255, 255, 0);">"MALE BOVINE MANURE!!=
!" </span></font></pre></div><div dir=3D"ltr"><br><blockquote type=3D"cite">=
On 11 Jul 2024, at 15.19, Cuttler, Brian R (HEALTH) <brian.cuttler@health=
.ny.gov> wrote:<br><br></blockquote></div><blockquote type=3D"cite"><div d=
ir=3D"ltr">=EF=BB=BF
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<p class=3D"MsoNormal">Sten,<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Okay, pretty much what I=E2=80=99d thought, just neve=
r actually saw it before.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Reservations don=E2=80=99t protect the IP, the right a=
nswer here is to change to limits on the dynamic pool and make sure my reser=
vations are outside of the pool<o:p></o:p></p>
<p class=3D"MsoNormal">I=E2=80=99m actually wondering why I have a reservati=
on for this at all, that would also have resolve the issue, and would have n=
ot caused the users an issue as that subnet creates DDNS entries for us.<o:p=
></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">An entry like this?<br>
boot.log.2:May 5 08:42:28 cedar dhcpd[863]: Remove host declaration su=
raj or remove 10.50.148.212<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">I don=E2=80=99t routinely scan the dhcp logs, will ma=
ybe have to create a job to find such messages and notify me.<o:p></o:p></p>=
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Our static entries by and large are non-global, they a=
re within the stanza but that hasn=E2=80=99t been a problem, will look to ma=
ke updates as time allows.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Joe, Nilesh, without CC=E2=80=99d the list, can you s=
ee any reason why we need a reserved IP for Suraj?<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Thanks,<o:p></o:p></p>
<p class=3D"MsoNormal">Brian<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<div>
<div style=3D"border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0=
in 0in">
<p class=3D"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 <[email protected]><br>
<b>Subject:</b> Re: two hosts with the same IP<o:p></o:p></p>
</div>
</div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
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<p align=3D"center" style=3D"text-align:center;line-height:105%"><i><span st=
yle=3D"font-size:10.0pt;line-height:105%;color:yellow">ATTENTION: This email=
came from an external source. Do not open attachments or click on links fro=
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<p class=3D"MsoNormal"><o:p> </o:p></p>
<div>
<p class=3D"MsoNormal">I believe there should be a specific warning in the l=
og during startup.<o:p></o:p></p>
<div>
<pre><span style=3D"font-family:".SFUIDisplay-Regular",serif">-- B=
est regards</span><o:p></o:p></pre>
<pre><span style=3D"font-family:".SFUIDisplay-Regular",serif">Sten=
Carlsen</span><o:p></o:p></pre>
<pre><span style=3D"font-family:".SFUIDisplay-Regular",serif">No i=
mprovements come from shouting:</span><o:p></o:p></pre>
<pre><span style=3D"font-family:".SFUIDisplay-Regular",serif">"MAL=
E BOVINE MANURE!!!" </span><o:p></o:p></pre>
</div>
<div>
<p class=3D"MsoNormal"><br>
<br>
<o:p></o:p></p>
<blockquote style=3D"margin-top:5.0pt;margin-bottom:5.0pt">
<p class=3D"MsoNormal" style=3D"margin-bottom:12.0pt">On 11 Jul 2024, at 02.=
23, Glenn Satchell <<a href=3D"mailto:[email protected]">Glenn.S=
[email protected]</a>> wrote:<o:p></o:p></p>
</blockquote>
</div>
<blockquote style=3D"margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class=3D"MsoNormal">=EF=BB=BF <o:p></o:p></p>
<div>
<div>
<div>
<p class=3D"MsoNormal">hi Brian,<o:p></o:p></p>
</div>
<div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class=3D"MsoNormal">fixed-address assignments must be outside the pool of=
dynamic addresses to prevent this situation.<o:p></o:p></p>
</div>
<div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class=3D"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 assign=
ed.<o:p></o:p></p>
</div>
<div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class=3D"MsoNormal">This is mentioned in the docs, dhcpd.conf man page i t=
hink.<o:p></o:p></p>
</div>
<div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class=3D"MsoNormal">regards,<br>
Glenn<o:p></o:p></p>
</div>
</div>
<div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<div>
<p class=3D"MsoNormal">On 11 July 2024 6:12=E2=80=AFam, "Cuttler, Brian R (H=
EALTH)" <<a href=3D"mailto:[email protected]">brian.cuttler@hea=
lth.ny.gov</a>> wrote:<o:p></o:p></p>
<blockquote style=3D"border:none;border-left:solid #CCCCCC 1.0pt;padding:0in=
0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<div>
<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 t=
he IP was good, ping from the IP was problematic, lots of dropping pings in a=
bout 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 ke=
ys 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 r=
eceiving 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 b0:7=
b: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 (be=
rkeley) 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 (10.50.15=
6.21) 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> &=
nbsp; hardware ethernet d4:5d:64:08:91:7c;<o:p></o:p></p>
<p> &=
nbsp; fixed-address 10.50.148.212;<o:p></o:p></p>
<p> &=
nbsp; }<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=E2=80=99m very surp=
rised by the behavior we were seeing.<br>
If the non-received MAC received the IP wouldn=E2=80=99t the MAC with the re=
servation still cause a ping test for availability to be performed?<br>
I can=E2=80=99t 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 p=
revent 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=3D"font-size:12.0pt;font-family:"Arial",serif">Bria=
n Cuttler, System and Network Administration</span><o:p></o:p></p>
<p><span style=3D"font-size:12.0pt;font-family:"Arial",serif">Wads=
worth Center, NYS Department of Health</span><o:p></o:p></p>
<p><span style=3D"font-size:12.0pt;font-family:"Arial",serif">Alba=
ny, NY 12201 POB 509</span><o:p></o:p></p>
<p><span style=3D"font-size:12.0pt;font-family:"Arial",serif"><a h=
ref=3D"mailto:[email protected]"><span style=3D"color:#0563C1">Bri=
[email protected]</span></a></span><o:p></o:p></p>
<p><span style=3D"font-size:12.0pt;font-family:"Arial",serif">518 4=
86-1697</span><o:p></o:p></p>
<p> <o:p></o:p></p>
</div>
</div>
</blockquote>
</div>
<p class=3D"MsoNormal"><o:p> </o:p></p>
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