[Dnsmasq-discuss] can't take away IPv4 address

Simon Kelley simon at thekelleys.org.uk
Wed Aug 26 22:25:35 BST 2015


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On 26/08/15 07:57, Harald Dunkel wrote:
> Hi Simon,
> 
> On 08/25/15 23:18, Simon Kelley wrote:
>> 
>> Dnsmasq does the check which the standards require, which is to
>> send an ICMP ping (echo request) to the address it's about to
>> allocate. The fact that the client doesn't respond would seem to
>> indicate that the clients are NOT using IP addresses after the
>> lease has expired.
>> 
> 
> I think the ping test would be pretty helpful.
> 
> The IPv4 address range is set to 10.10.0.0/16. Lease time is 1h. 
> There are less than 200 DHCP clients in my net. Even without ping 
> test it should be easy to avoid a conflict.
> 
>> My guess is that what's happening here is that the ARP-table
>> entry on the server persisting after the lease expires. When the
>> IP address is given to a new client, dnsmasq updates the ARP
>> table, and those are just warnings that the ARP table for
>> 10.10.123.204 is being overwritten.
>> 
> 
> That would mean its a one-time event within the lease time. Looking
> at the log file it seems to me that both clients keep on using the
> same IP address for days and that the ARP entry for the conflicting
> IP address is overwritten again and again within a few minutes.
> 
> BTW, I found both devices of my test case: Its an AppleTV 2 and an 
> old Airport. I gave the Airport a static IP address 10.10.255.254. 
> It started using it, but the ARP warnings about 10.10.123.204 and 
> the Airport's MAC address continued to popup in the logfile. After 
> a power cycle of the Airport the warnings are gone.
> 

That's pretty strong evidence of mis-behavior, but I don't understand
how neither dnsmasq (using ICMP ping) or the DHCP clients (using ARP)
are noticing these hosts still camping on the IP addresses.



Cheers,

Simon.

> 
> Hope this helps. Regards Harri
> 
> 
> 
> _______________________________________________ Dnsmasq-discuss
> mailing list Dnsmasq-discuss at lists.thekelleys.org.uk 
> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
> 

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