[Dnsmasq-discuss] Slow response to DHCPDISCOVER

Wed Apr 25 04:53:46 BST 2012

Daryl may still be correct.  Linux's bridge module also implements the
learning phase (for detection of loops) before it begins forwarding packets.

On Tue, Apr 24, 2012 at 10:38 PM, Adrian May <adrian.may at oregan.net> wrote:

> Hi Daryl,
>
> There is no switch. I'm trying to build a router and I'm plugging clients
> directly into it. It's actually a little fanless thing with 8 ethernet
> ports, 7 of which I bridge to make the private LAN, and the other of which
> dials pppoe. I installed ubuntu server 10.04, followed by the bridge, and
> then dnsmasq.
>
> In the meantime, I got another result. With IPFire, I found dhcp very
> fast, and it turned out that some of the home made cables around here can't
> connect the embedded boards to the little box I'm making the router out of.
> But they can connect any PC to my router or the 10 dollar router, and they
> can connect any PC or embedded board to the 10 dollar router, and the
> proper cables can connect anything to anything. In other words, the only
> combination that doesn't work is the home-made cable connecting the
> embedded boards to my new router. What's more, it doesn't matter whether I
> use a 100Mb or 1Gb socket on the new router. Very strange. That's all under
> IPFire, so now I'm reinstalling ubuntu to see if I get the same result.
>
> Adrian.
>
>
>
>
> On 04/24/2012 10:51 PM, Daryl Richards wrote:
>
>> Actually, the "10 dollar domestic router" fix points to the probable
>> solution. You likely have spanning tree turned on on your usual switch,
>> which will block all traffic on that port for the first 50 seconds after
>> a link state change. Either switch to rapid spanning tree, or look into
>> your switch's version of "portfast"..
>>
>> On 12-04-23 11:21 PM, 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?
>>>
>>> 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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