DHCPOFFER NACKed upon first REQUEST - SOLVED

[Glenn Satchell]

On Thu, April 3, 2014 12:48 am, Daniele Albrizio wrote:
> On 17/03/2014 19:34, Peter Rathlev wrote:
>> On Mon, 2014-03-17 at 17:33 +0100, Daniele Albrizio wrote:
>>> Some clients (quasi 40 out of 2000) are being NACKed just after
>>> offering
>>> a lease like this:
>>>
>>> Mar 17 14:27:48 luna dhcpd: DHCPDISCOVER from 74:f0:6d:0c:6e:6f ...
>>> Mar 17 14:27:48 luna dhcpd: DHCPOFFER on 140.105.105.75 to ...
>>> Mar 17 14:27:48 luna dhcpd: DHCPREQUEST for 140.105.105.75 ...: lease
>>> 140.105.105.75 unavailable.
>>> Mar 17 14:27:48 luna dhcpd: DHCPNAK on 140.105.105.75...
>>
>> We have seen some clients using a DISCOVER for what should be a REQUEST,
>> since they had an already valid lease and had the address configured and
>> replying to ICMP echoes. But you have "ping-check" set to false in the
>> configuration you posted, so that shouldn't be it.
>>
>> Maybe not terribly constructive, but if you're running DHCPd v3 (which I
>> have a feeling you do) you should seriously consider upgrading. Many
>> many things have been fixed the last decade-or-so.
>
> dhcp3 is the old name of the config dir, dhcpd is instead Debian's
> flavour of isc dhcpd 4.2.2
>
> But, hear the news! I found how to reproduce this behaviour.
>
> The problem arised when I forgot an orphan /24 subnet in a far away
> network segment (shared network) included in the running configuration
> of dhcp.
> I then reused the addresses inside an /23 network in another shared
> network with other 6 pools in other 6 subnets.
>
> This misconfiguration lead in nacking just offered ip addresses not
> necessarily inside that subnet but in the whole address space of the
> shared network for some same clients variyng at each server restart.
>
> What is worse is that some (a lot of) clients once nacked a just offered
> address will immediately discover for another one.
>
> Result: server and network flooded with requests. Connectivity disrupted
> also for static clients.
>
> --
Hi Daniele

Nice work! Good to hear you found a real cause of the problem and were
able to fix it. I hate those weird problems which seem to just go away and
you wonder whether it's really fixed or not.

ciao
-glenn