Script to run on DHCPNAK

Thu Jul 20 18:26:28 UTC 2017

Mark, 

Is it the ISC server that is also handing out the 192.168.100.20 address or a different DHCP server? If its all the same server, I'm thinking class {} statements and allow members of "class"; would be the appropriate fix right inside the DHCP config... 

If it is a different DHCP server that is ALSO ISC that you could modify, you could use class {} statements in there to cause it to ignore booting from clients it shouldn't serve. 

> From: "Mark Spring" <mspring at nktelco.com>
> To: "Users of ISC DHCP" <dhcp-users at lists.isc.org>
> Sent: Thursday, July 20, 2017 8:53:11 AM
> Subject: Re: Script to run on DHCPNAK

> The trouble is that the end device boots too quick and grabs the 192 address
> from the modem(cable labs spec) then moments later it halts and asks for all
> the information that would normally be in the DHCP options. The lease from the
> modem expires, it requests...server NAK's it. It then gets all the proper info
> but the client doesn't read in all of the options. In a perfect world I have
> advised the vendor to read in the options and continue with the client. In the
> real world, I am trying to setup things so when I see a NAK, I execute a
> script...if it matches an OUI then I lookup the IP that it received, SSH into
> the client and reboot it. The modem is online and everything starts up normal.
> We are essentially building a reboot script into the client where it reboots if
> it fails to receive options the first time around.
> Hope this helps, thanks for replying!

> Mark Spring
> Information Systems Manager

> On Thu, Jul 20, 2017 at 8:45 AM, perl-list < [ mailto:perl-list at network1.net |
> perl-list at network1.net ] > wrote:

>> Mark,

>> That is completely normal. The device 00:03:e6:6f:42:14 previously had an
>> address of 192.168.100.20 and attempted to renew such address. Apparently that
>> address is not valid on the network your DHCP server is on. So, a NAK was sent
>> followed by a discover from the client. The client and server then negotiated a
>> 10.4.2.191 address.

>> What is the actual problem that you are having as I am not sure this has
>> anything to do with it...

>>> From: "Mark Spring" < [ mailto:mspring at nktelco.com | mspring at nktelco.com ] >
>>> To: "Users of ISC DHCP" < [ mailto:dhcp-users at lists.isc.org |
>>> dhcp-users at lists.isc.org ] >
>>> Sent: Thursday, July 20, 2017 8:31:30 AM
>>> Subject: Re: Script to run on DHCPNAK

>>> isc, just one server here is an example
>>> Jul 19 10:04:36 dhcp dhcpd: DHCPREQUEST for 192.168.100.20 from
>>> 00:03:e6:6f:42:14 via [ http://10.4.0.1/ | 10.4.0.1 ] : wrong net
>>> Jul 19 10:04:36 dhcp dhcpd: DHCPNAK on 192.168.100.20 to 00:03:e6:6f:42:14 via
>>> 10.4.0.1
>>> Jul 19 10:04:39 dhcp dhcpd: DHCPDISCOVER from 00:03:e6:6f:42:14 via 10.4.0.1
>>> Jul 19 10:04:40 dhcp dhcpd: DHCPOFFER on 10.4.2.191 to 00:03:e6:6f:42:14 via
>>> 10.4.0.1
>>> Jul 19 10:04:40 dhcp dhcpd: DHCPREQUEST for 10.4.2.191 (192.168.100.3) from
>>> 00:03:e6:6f:42:14 via 10.4.0.
>>> Jul 19 10:04:40 dhcp dhcpd: DHCPACK on 10.4.2.191 to 00:03:e6:6f:42:14 via
>>> 10.4.0.1

>>> Mark Spring
>>> Information Systems Manager

>>> On Thu, Jul 20, 2017 at 8:22 AM, perl-list < [ mailto:perl-list at network1.net |
>>> perl-list at network1.net ] > wrote:

>>>> Are the NAK and ACK coming from the same server? Can you post example log
>>>> messages of the NAK and ACK and related communication? I assume this is ISC
>>>> DHCP that we are speaking of and not some proprietary DHCP server?

>>>>> I am having some issues with network gear, and while arguing with vendors about
>>>>> who's problem it really is..I noticed that my device receives a NAK before it
>>>>> receives the proper IP address from our server(when the gear comes back
>>>>> online). If I can track this down in the logs then I can look for the ACK that
>>>>> follows, login to the device and reboot it properly.

>>>>> ___
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> NKTelco
> 301 W. South St.
> New Knoxville, OH 45871

> Phone: 1-888-NKTELCO
> Fax: 419-753-2950

> This message and the file(s) attached are confidential and proprietary
> information of NKTelco for the sole use of the intended recipient. Any
> unauthorized review, distribution, disclosure, copying, use, or
> dissemination, either whole or in part, is strictly prohibited. Do not
> transmit these documents, in any form, to any third party without the
> expressed written permission of NKTelco.

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