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

[Harald Dunkel]

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.


Hope this helps. Regards
Harri

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