[Dnsmasq-discuss] IP assigning for wrong network

Simon Kelley simon at thekelleys.org.uk
Mon Feb 24 11:54:06 UTC 2014


On 22/02/14 22:58, Tamas Papp wrote:
> 
> On 02/20/2014 06:12 PM, Simon Kelley wrote:
>> On 19/02/14 23:03, Tamas Papp wrote:
>>> hi All,
>>>
>>>
>>> Feb 19 23:49:48 workhorse dnsmasq-dhcp[6678]: DHCPINFORM(eth-clients)
>>> 10.0.1.233 70:54:d2:1b:18:59
>>> Feb 19 23:49:48 workhorse dnsmasq-dhcp[6678]: DHCPACK(eth-clients)
>>> 10.0.1.233 70:54:d2:1b:18:59 vweiszfeiler-pc
>>> Feb 19 23:49:51 workhorse dnsmasq-dhcp[6678]: DHCPINFORM(eth-clients)
>>> 10.0.1.233 70:54:d2:1b:18:59
>>> Feb 19 23:49:51 workhorse dnsmasq-dhcp[6678]: DHCPACK(eth-clients)
>>> 10.0.1.233 70:54:d2:1b:18:59 vweiszfeiler-pc
>>>
>>
>> So, in that log fragment there's no assignment going on. The client is
>> asking for configuration information, and dnsmasq is sending it. The
>> only thing dnsmasq could do differently is to ignore the DHCPINFORM
>> when the IP address the client sends is not on the network that the
>> client appears to be on, but that bfreaks other, useful use-cases fro
>> DHCPINFORM.
> 
> What is the reason they do this?
> It doesn't make sense to me. I mean if they are just chatting, but don't
> do anything, then no reason. 

The clients are not using DHCP to get IP addreses (at least not using
DHCPINFORM they might have get a DHCP lease earlier, or they might have
been manually configured. The purpose of DHCPINFORM is for the client to
ask for _other_ configuration information: address of DNS servers, NTP
servers, routing information, etc etc. That's what is sent in the DHCPACK.
> In my logic (just human logic, I don't know
> rfc:) the dhcp should send DHCPNAK to let the client know about the
> situation.

My reading of the standard is that a DHCPNAK is not allowed as an answer
to DHCPINFORM
> What else could be the goal of DHCPINFORM? Maybe informing the server,
> that the client is using that IP address?
> 

No. The DHCPINFORM says "The client is using this address, and would
like other configuration information, please reply with that information
(which may depend on the IP address).



Cheers,

Simon.


>> If/when the client does DHCPREQUEST and attempts to renew the lease,
>> dnsmasq should respond with with DHCPNAK and then the client will move
>> IP addresses. When that happens depends on when the lease expires.
> 
> I see, thanks.
> 
> tamas
> 




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