dhcpcd-discuss

On Thu, Apr 4, 2013 at 3:25 PM, Roy Marples <roy@xxxxxxxxxxxx> wrote:

> On 04/04/2013 23:18, Kobi Cohen-Arazi wrote:
>
>> On Thu, Apr 4, 2013 at 3:10 PM, Roy Marples <roy@xxxxxxxxxxxx> wrote:
>>
>>  On 04/04/2013 22:20, Roy Marples wrote:
>>>
>>>  In this specific scenario, the target DHCPD server is not the same
>>>>> one giving this IP to the client so it remains silent. (this is by the
>>>>> spec IMO).
>>>>> client backs off for 10 second and start again with DISCOVER. From
>>>>> this point everything goes as it should be.
>>>>>
>>>>
>>> I would also point out that it's recommended these days that DHCP
>>> servers are authorative which means they should NAK any invalid address.
>>> Only non authorative DHCP servers would remain silent.
>>>
>>
>> Totally agree with you on this one. This would solve my issue. There
>> is a "but" :) here:
>> What I noticed is that if your client moved from one IP subnet config
>> network (say 192.168.1.0/24) to another network with a different
>> IP subnet config network (e.g. 10.10.1.0/24), then DHCP will
>> NAK immediately (well, I still needed to config "always-reply-rfc1048"
>> on the DHCP server).
>> But if the client moved from one network to another network and both
>> networks have the same IP subnet config (e.g. both has 192.168.1.0/24
>> [1]) then DHCP will *not* NAK despite always-reply-rfc1048 is on.
>>
>> Simple googling shows that it is really the expected behavior.
>>
>
> I would not expect that behaviour.
> Can you provide links where this is the case?
>

http://manpages.ubuntu.com/manpages/intrepid/man5/dhcpd.conf.5.html

Here is the confusing part:


       If the server knows nothing
       about the address,  it  will  remain  silent,  unless  the  address  is
       incorrect for the network segment to which the client has been attached
       and the server is authoritative for that network segment, in which case
       the  server  will  send a DHCPNAK even though it doesn’t know about the
       address.


In other words, my client had 192.168.1.10 from network A and I moved to
network B which happen to have the same IP network config and client issue
a DHCP request, DHCP server (which knows nothing about the client having
this IP) will remain silent even if it is authoritative.

In another words - server knows nothing about the address, BUT the address
*is* correct for the network segment, so it will keep silent.
If server knows nothing about the address AND the address is incorrect for
this network subnet (e.g. 10.10.1.10) AND server is autoritative, then
server replies with NAK.

I might be wrong here, but this is how I understand the above.



>
> Also, I'm not clear how always-reply-rfc1048 would affect NAK?
>

Sorry, I actually meant "authoritative;" though I also use
"always-reply-rfc1048 on;" in my /etc/dhcp/dhcpd.conf.

Thanks,
Kobi