two hosts with the same IP
"Cuttler, Brian R (HEALTH)" <[email protected]> Wed, 10 Jul 2024 20:12:39 +0000
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Running DHCP on Ubuntu 22.04.4 LTS
brian@cedar:/var/log$ DHCP -V
Internet Systems Consortium DHCP Server 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
Noted one system in particular was having network issues, ping to the IP w=
as good, ping from the IP was problematic, lots of dropping pings in about =
25 second groups/blocks.
Also having trouble maintaining SSH connection into the host, and host keys=
needed to be removed and reaccepted.
On a hunch I checked the dhcp log and found two different MAC addresses rec=
eiving the same IP.
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
Jul 9 11:49:38 cedar DHCP[1019]: DHCPACK on 10.50.148.212 to d4:5d:64:08:9=
1:7c via 10.50.148.1
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
Jul 10 15:04:17 cedar DHCP[1019]: DHCPACK on 10.50.148.212 to b0:7b:25:de:5=
7:84 (berkeley) via 10.50.148.1
Jul 10 15:05:16 cedar DHCP[1019]: DHCPDISCOVER from b0:7b:25:de:57:84 (berk=
eley) via 10.50.148.1
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
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
Jul 10 15:05:16 cedar DHCP[1019]: DHCPACK on 10.50.148.212 to b0:7b:25:de:5=
7:84 (berkeley) via 10.50.148.1
I also note that one of the two hosts has a reservation.
host Suraj {
hardware ethernet d4:5d:64:08:91:7c;
fixed-address 10.50.148.212;
}
While I realize that a host with a reservation might be down, and another m=
achine could get the IP if its in the available pool I'm very surprised by =
the behavior we were seeing.
If the non-received MAC received the IP wouldn't the MAC with the reservati=
on still cause a ping test for availability to be performed?
I can't think of any other way this could have happened.
Can anyone help me to understand what actually happened and how best to pre=
vent similar events in the future?
thanks in advance,
Brian
Brian Cuttler, System and Network Administration
Wadsworth Center, NYS Department of Health
Albany, NY 12201 POB 509
[email protected]<mailto:[email protected]>
518 486-1697
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<p class=3D"MsoNormal">Running DHCP on Ubuntu 22.04.4 LTS<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">brian@cedar:/var/log$ DHCP -V<o:p></o:p></p>
<p class=3D"MsoNormal">Internet Systems Consortium DHCP Server 4.4.1<o:p></=
o:p></p>
<p class=3D"MsoNormal">Copyright 2004-2018 Internet Systems Consortium.<o:p=
></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Noted one system in particular was having netw=
ork 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 class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Also having trouble maintaining SSH connection into =
the host, and host keys needed to be removed and reaccepted.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">On a hunch I checked the dhcp log and found two diff=
erent MAC addresses receiving the same IP.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Jul 9 11:49:38 cedar DHCP[1019]: DHCPREQUEST f=
or 10.50.148.212 from d4:5d:64:08:91:7c via 10.50.148.1<o:p></o:p></p>
<p class=3D"MsoNormal">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 class=3D"MsoNormal">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 class=3D"MsoNormal">Jul 10 15:04:17 cedar DHCP[1019]: DHCPACK on 10.50.1=
48.212 to b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p class=3D"MsoNormal">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 class=3D"MsoNormal">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 class=3D"MsoNormal">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 class=3D"MsoNormal">Jul 10 15:05:16 cedar DHCP[1019]: DHCPACK on 10.50.1=
48.212 to b0:7b:25:de:57:84 (berkeley) via 10.50.148.1<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">I also note that one of the two hosts has a reservat=
ion.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal"> host Sura=
j {<o:p></o:p></p>
<p class=3D"MsoNormal"> &nbs=
p; hardware ethernet d4:5d:64:08:91:7c;=
<o:p></o:p></p>
<p class=3D"MsoNormal"> &nbs=
p; fixed-address 10.50.148.212;<o:p></o=
:p></p>
<p class=3D"MsoNormal"> &nbs=
p; }<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">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 res=
ervation 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 class=3D"MsoNormal"><o:p> </o:p></p>
<p class=3D"MsoNormal">Can anyone help me to understand what actually happe=
ned and how best to prevent similar events in the future?<br>
<br>
thanks in advance,<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>
<p class=3D"MsoNormal"><span style=3D"font-size:12.0pt;font-family:"Ar=
ial",serif;mso-ligatures:none">Brian Cuttler, System and Network Admin=
istration<o:p></o:p></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:12.0pt;font-family:"Ar=
ial",serif;mso-ligatures:none">Wadsworth Center, NYS Department of Hea=
lth<o:p></o:p></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:12.0pt;font-family:"Ar=
ial",serif;mso-ligatures:none">Albany, NY 12201 POB 509<o:p></o:p></sp=
an></p>
<p class=3D"MsoNormal"><span style=3D"font-size:12.0pt;font-family:"Ar=
ial",serif;mso-ligatures:none"><a href=3D"mailto:Brian.Cuttler@Health.=
NY.gov"><span style=3D"color:#0563C1">[email protected]</span></a=
><o:p></o:p></span></p>
<p class=3D"MsoNormal"><span style=3D"font-size:12.0pt;font-family:"Ar=
ial",serif;mso-ligatures:none">518 486-1697</span><span style=3D"font-=
size:12.0pt;font-family:"Arial Nova",sans-serif;mso-ligatures:non=
e"><o:p></o:p></span></p>
<p class=3D"MsoNormal"><o:p> </o:p></p>
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