[Dnsmasq-discuss] Slow response to DHCPDISCOVER

[Simon Kelley]

On 24/04/12 04:21, Adrian May wrote:
> Hi Simon,
>
> In the meantime I installed ClearOS, which uses dnsmasq. Now the PCs get
> served fast but my embedded boards are still not getting IPs. If I plug
> these embedded boards into my 10 dollar domestic router, they get an IP
> instantly. I already tried setting bootp-dynamic and dhcp-broadcast in
> the config. If I grep everything under /var/log for dnsmasq, there's no
> evidence that requests were even received from these boards. So I still
> suspect the networking layer.
>
> As for the boards themselves, I'm not entirely sure what they do.
> They've got some kind of embedded linux. One boots into yamon where I
> can only say "net init", the other into something of its own invention
> where I start udhcpc.
>
> I tried no-ping but it had no effect. I can't get my brain around your
> tag system. I've just been writing things like bootp-dynamic with no
> tags right in the main config file, or in the case of ClearOS, in the
> dhcp config file which is referenced from the main config file. Could it
> be that these settings have no effect unless I attach some tags, or put
> them inside a subnet declaration?
>

No tags -> applies everywhere, so that's not the problem.

Do you have some combination of --interface, --listen-address and 
--dhcp-except that's telling dnsmasq not to do DHCP on the network these 
things are plugged into? Can you plug a laptop or something into the 
same port and get a DHCP lease?

If you can narrow it down to just these embedded boards, then we'll have 
to start looking at packet dumps.


Cheers,

Simon.

> Adrian.
>
>
>
> On 04/23/2012 08:01 PM, Simon Kelley wrote:
>> On 23/04/12 12:02, Adrian May wrote:
>>>
>>> Hi all,
>>>
>>> I get the same result with dnsmasq, dhcp3-server and isc, namely, that
>>> the client has to send several DHCPDISCOVER packets before the server
>>> finally responds after about 30 seconds. This is breaking a couple of
>>> embedded platforms because they aren't that patient, and I have no way
>>> of configuring that.
>>>
>>> Why don't DHCP servers just respond to the first DHCPDISCOVER?
>>> Especially when I made them authoritative?#
>>
>> Servers allocate an address and then ping it for a few seconds just to
>> be sure it's not in use. That's the main delay. In dnsmasq --no-ping
>> will stop this behaviour. Also the client is entitled to wait around
>> collecting answers from more than one server before deciding which one
>> to use; they rarely do this and it doesn't sound like yours are.
>>>
>>> I think I might have seen in the logs that the dhcp processes aren't
>>> even getting the earlier packets, even though the machine is. It's as if
>>> they get discarded by the networking layer. This is a ubuntu server
>>> 10.04 machine.
>>
>>
>> Firewall rules can affect things, but the result is rarely
>> intermittent. Is your network heavily loaded and dropping packets?
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>>
>>> Any ideas?
>>>
>>> Adrian.
>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>> Dnsmasq-discuss at lists.thekelleys.org.uk
>>> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
>>>
>>
>>
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