Re: [Dnsmasq-discuss] No Broadcast Dhcp Offers

[gravity70]

Hi Geert,

thanks for the answer.

 

>>I don't buy that. ARP also does ethernet broadcasts.
>>Without Address Resolution Protocol no IPv4 networking on ethernet.

 

Sorry dont understand what you dont buy, i'm not selling anything here ;-)

 

Amof, the first and only frames my dongle sends on eth at start, are some Dhcp DISCOVER, no arps at all.

Please note that such Dhcp DISCOVER frames come with the broadcast bit NOT set.

Afaik, that meas my dongle is indeed asking the Dhcp server to send a unicast response, directly to its mac.

Instead QNSMASQ sends those Dhcp OFFER frames to broadcast.

Why it happens so?

 

>>What I think is that no driver is loaded for the dongle during first DHCP Discover request.

>>Then just write your own DHCP server. ;-)

 

In fact I already did that, on server side I wrote few codes of C program which binds to eth.

It listens to QNSMASQ Dhcp OFFER frames messages with eth.dst=ff:ff:ff:ff:ff:ff.

When such frames arrive, it simply re-inject exactly the same frames in eth, but with eth.dst=<mac dongle> .

It works, dongle answers with REQUEST, then ACK, then all goes smoothly no problems.

 

As you can understand, that is just a very dirty workaround, can use it only to test the correct connectivity and driver load, because unfortunately I cant do nothing on the dongle side.

But can't use that thing in production...

Any hint for a decent solution to suggest me?

Thank you

 

 

Sent: Sunday, September 23, 2018 at 9:33 AM
From: "Geert Stappers" <stapp...@stappers.nl>
To: dnsmasq-discuss@lists.thekelleys.org.uk
Subject: Re: [Dnsmasq-discuss] No Broadcast Dhcp Offers

On Sat, Sep 22, 2018 at 07:06:53PM +0200, gravit...@gmx.com wrote:
> Hi all,
> I have a very simple question, but it seems difficult to find a solution...
>
> By default DNSMASQ sends Dhcp OFFER message with eth.dst=ff:ff:ff:ff:ff:ff , it
> sends to broadcast mac.
> I have a dongle which works a bit outside specs, and can't answer to broadcast
> mac.

I don't buy that. ARP also does ethernet broadcasts.
Without Address Resolution Protocol no IPv4 networking on ethernet.

What I think is that no driver is loaded for the dongle
during first DHCP Discover request.


> So, I need DNSMASQ to send the Dhcp OFFER messages (and better also ACK/NAK and
> the whole Dhcp stack) to a specific mac I set.
> Does it exist such option?

I don't know.


> I already was thinking to start crafting Dhcp frames myself... but I dont
> really want to rewrite my own DNSMASQ...

Then just write your own DHCP server. ;-)


Groeten
Geert Stappers
--
Leven en laten leven

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