Daniele Albrizio albrizio at univ.trieste.it
Wed Apr 2 13:48:19 UTC 2014

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 to ...
>> Mar 17 14:27:48 luna dhcpd: DHCPREQUEST for ...: lease 
>> unavailable.
>> Mar 17 14:27:48 luna dhcpd: DHCPNAK on
> 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.

   Daniele ALBRIZIO - albrizio at univ.trieste.it
           Tel. +39-040.558.3319
    UNIVERSITY OF TRIESTE - Network Services
Divisione V - Infrastrutture e Servizi Informativi
  via Alfonso Valerio, 12 I-34127 Trieste, Italy
Sezione Infrastrutture Informatiche e Telematiche

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