[Dnsmasq-discuss] ARP ignores DHCP ACKs !

Albert ARIBAUD albert.aribaud at free.fr
Tue Dec 24 12:45:03 GMT 2013

Le 24/12/2013 13:35, Nikita N. a écrit :
> Hi :) Im having a strange issue here with DHCP/ARP I cant solve..
> DHCP works good, it receives a REQ from client MAC asking the preferred
> ip, e.g., and DHCP answers correctly ACK..
> But after that, my client keeps asking the following ARP requests to
> broadcast: "Who has Tell" .. it expects the answer
> like " is at XX.XX.XX.XX.XX", where XX is the client MAC..
> but it never comes :(
> those ARP frames are generated by the client (source=XX) and never
> receive any answer..
> on the opposite, when the client sends ARPs requesting the GW (Who has
> the ARP responses come correctly pointing to the correct
> GW MAC..
> It looks like dnsmasq does NOT inform the system ARP about the client ip
> it just ACKed, resulting always in connection error/absent ..
> So, my question is, how can I instruct dnsmasq to inform the system ARP
> with the new client MAC/ip, after DHCP sent correctly the ACK?
> Thanks :)

As far as I can tell, the answer to an ARP request comes from the actual 
owner of the IP, not from the DHCP server which gave it.

You should do a tcpdump/wireshark on the client, to see if it actually 
sees and handles the DHCP ACK. If for some reason it does not, then that 
might explain why it asks on ARP for its own address.


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