[Dnsmasq-discuss] ARP ignores DHCP ACKs !

Simon Kelley simon at thekelleys.org.uk
Tue Dec 24 19:22:02 GMT 2013

On 24/12/13 12:35, Nikita N. wrote:
> 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 :(

Are you sure about the order of these events? Most DHCP clients will 
check that the address they've been offered is not in use by anonther 
machine before accepting it, and they do that by sending ICMP echo 
requests. To send the echo request, the client's kernel will need to 
send ARP requests and that probably what you are seeing.

I'd expect to see the client sending these ARPs _afer_ the DHCPOFFER and 
before the DHCPREQUEST.



> 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 :)

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