[Dnsmasq-discuss] Re: DHCP: different IPs for same same MAC

[Jan 'RedBully' Seiffert]

Sven Köhler wrote:
>>>  here's the leases file from a currently running dnsmasq installation:
>>>  86400 00:12:f0:a1:81:7d 10.1.2.233 bert 01:00:12:f0:a1:81:7d
>>>  86400 00:12:f0:a1:81:7d 10.1.2.22 *
>>> ff:65:74:68:31:00:01:00:01:0e:91:06:82:00:00:f0:7a:14:04
>>>
>>>  How can that be? Same MAC-addresses, but different IPs?
>>>
>>>  Well, if i boot Linux on this comuter, it get's the 10.1.2.22.
>>>  If i boot Windows, then it get's the 10.1.2.233. Why is that?
>>>  (BTW: if i delete the leases file, restart dnsmasq, and boot windows 
>>> first,
>>> then windows get's the 22 and linux get's the 233).
>>
>> One is sending a client ID and one is not.  The fact that switching
>> them reverses it seems odd to me, since I would have a possible
>> explanation if it didn't...
> 
> My guess is, that the two DHCP-requests by the two OS differ - and 
> dnsmasq compares them, and then says: oh, different DHCP request, so 
> let's give him a different IP (which seems completely beyond the idea of 
> DHCP to me, since leases-file should only be a MAC->IP mapping).
> 

In dnsmasq, client-ID overrides MAC-Address, and thats the difference 
between the two requests.
I was bitten by this when my linux-distro updated the dhcpc, now sending 
a random id, when sending none before...

so you want to change in your dnsmasq.conf:
dhcp-host=00:00:F0:7A:14:04  ,  10.1.2.21 #bert
to
dhcp-host=00:00:F0:7A:14:04  , id:* , 10.1.2.21 #bert

Greetings
	Jan

-- 
The Theorem Theorem: If If, Then Then.