[Dnsmasq-discuss] Do "proxy-DHCP" without PXE

[Steven Maddox]

Thanks Simon,

I had a feeling it would be something like that... I can stop trying to 
make the impossible happen now! :D

Steven Maddox
Lantizia

On 29/04/2025 09:41, Simon Kelley wrote:
> 
> 
> On 29/04/2025 06:58, Steven Maddox wrote:
>> Ah and I just realised the final sentence I used in my original post 
>> said 'what' and not 'why' ... it meant to say...
>>
>> " But I have a feeling I'm going to be told that "proxy-DHCP" is, and 
>> can only be, a PXE specific thing?  if so, **why** is that? "
> 
> Exactly so. It's client behaviour that stops it, not server. The DHCP 
> protocol allows multiple _servers_ on a network, and the client 
> broadcasts, collects answers from potentially more than one, chooses 
> which one it likes best, and then transacts with that single server. 
> That's what the spec says, and that's what clients do.  Only PXE clients 
> have the ability to talk to both a DHCP server and a PXE server.
> 
> The only way to implement this that I can see is to put the clients you 
> want to mess with in a separate subnet with a DHCP relay back to the 
> main the DHCP server and make a relay that can add arbitrary options. 
> But that's kind of pointless, since if you've moved the phones (or 
> whatever) to a new subnet you may as well configure a DHCP server there.
> 
> Cheers,
> 
> Simon.
> 
> 
>>
>> Steven Maddox
>> Lantizia
>>
>> On 29/04/2025 06:55, Steven Maddox wrote:
>>> Hi Simon,
>>>
>>> I didn't know about that, I'll take a look at it.
>>>
>>> But I have a feeling that it's not what I'm after, as the scenario 
>>> I'm talking about doesn't involve any PXE clients.  See the example 
>>> scenario I gave before where I referred to a Polycom phone.
>>>
>>> Steven Maddox
>>> Lantizia
>>>
>>> On 28/04/2025 19:52, Simon Kelley wrote:
>>>> The latest release, 2.91, includes a new option --dhcp-option-pxe, 
>>>> which may be of use here.
>>>>
>>>> Cheers,
>>>>
>>>> Simon.
>>>>
>>>>
>>>> On 28/04/2025 13:32, Steven Maddox wrote:
>>>>> Hello,
>>>>>
>>>>> Sorry if what I'm about to ask is impossible, but I just really 
>>>>> needed to know one way or another.
>>>>>
>>>>> I find dnsmasq such a handy utility for all kinds of situations (so 
>>>>> huge thanks for creating it!)... one such situation was back when I 
>>>>> was working with ThinStation and I'd do something like this to 
>>>>> quickly test how a new build would boot on some PXE enabled 
>>>>> machines...
>>>>>
>>>>> dnsmasq -d -i enp2s0 -F192.168.1.0,proxy --enable-tftp --tftp- 
>>>>> root="$(pwd)/build/boot-images/pxe" -p0 --log-dhcp --pxe- 
>>>>> service=x86PC,'Network Boot',boot/lpxelinux/lpxelinux
>>>>>
>>>>> Ultimately it's the "proxy-DHCP" that I'm focussing on here.
>>>>>
>>>>> Would it be possible to use this technique to add extra arbitrary 
>>>>> DHCP options to a reply instead?  without touching the config of 
>>>>> the authoritative "other" DHCP server? e.g...
>>>>>
>>>>> dnsmasq -d -i enp2s0 -F192.168.1.0,proxy --enable-tftp --tftp- 
>>>>> root="$(pwd)" -p0 --log-dhcp -O 160,tftp://192.168.1.2
>>>>>
>>>>> This would be really handy in a scenario where you need to tell a 
>>>>> bunch of devices (e.g. Polycom phones) a new provisioning URL (in 
>>>>> that example option 160) on a temporary basis whilst you reboot/ 
>>>>> factory-reset them. Especially when you're stuck using whatever 
>>>>> existing DHCP server is on the network with no ability (or great 
>>>>> difficulty) to reconfigure it.
>>>>>
>>>>> But I have a feeling I'm going to be told that "proxy-DHCP" is, and 
>>>>> can only be, a PXE specific thing?  if so, what is that?
>>>>>
>>>>> Thanks
>>>>>
>>>>
>>>>
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