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

Simon Kelley simon at thekelleys.org.uk
Tue Aug 25 22:18:30 BST 2015


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On 25/08/15 07:33, Harald Dunkel wrote:
> Hi folks,
> 
> AFAICS there is no way for dnsmasq to make a client stop using an
> IPv4 address if the lease expires. Esp. some Apple and Android
> devices seem to play dirty.
> 
> Sure, they accept the new IP address via DHCP and start using it,
> but the old address is not dropped. Result is
> 
> : Aug 25 08:08:04 gate /bsd: arp info overwritten for 10.10.123.204
> by 00:1f:f3:08:xx:xx on re1 Aug 25 08:08:25 gate /bsd: arp info
> overwritten for 10.10.123.204 by 6c:94:f8:e2:yy:yy on re1 Aug 25
> 08:20:12 gate /bsd: arp info overwritten for 10.10.123.204 by
> 00:1f:f3:08:xx:xx on re1 Aug 25 08:20:25 gate /bsd: arp info
> overwritten for 10.10.123.204 by 6c:94:f8:e2:yy:yy on re1 Aug 25
> 08:20:26 gate /bsd: arp info overwritten for 10.10.123.204 by
> 00:1f:f3:08:xx:xx on re1 Aug 25 08:21:55 gate /bsd: arp info
> overwritten for 10.10.123.204 by 6c:94:f8:e2:yy:yy on re1 :
> 
> This is from /var/log/messages on the dnsmasq server. Of course,
> there is only one lease for this IP address (I checked). I wonder
> if dnsmasq could detect and work around this conflict?
> 

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.

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.



Cheers,

Simon.


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