Re: MVP for a DHCP server

[Roy Marples <roy%marples.name@localhost>]

 ---- On Tue, 15 Jul 2025 22:39:58 +0100  Mouse <mouse%Rodents-Montreal.ORG@localhost> wrote --- 
 > >>> You configure the DHCP client to [...]
 > >> You're assuming the DHCP client is configurable.  Sometimes (eg, PXE
 > >> boot ROMs), they're not.
 > > PXE does not need a static address.
 > 
 > PXE proper, no.  But (a) that was just one example of an unconfigurable
 > DHCP client and even with just PXE, (b) how would you address different
 > machines needing different kernels?
 > 
 > >> Any DHCP server which can't be configured to serve a client-specific
 > >> IP based on MAC address is a nonstarter for some of my, at least,
 > >> use cases.  (Which is not, of course, to say that such a feature is
 > >> necessary in an in-NetBSD-tree DHCP server.  I would like it if it
 > >> were, but NetBSD long ago stopped caring about what I like.)
 > > Sadly I do care about what people need.
 > 
 > Why "sadly"?

Because it takes me too long to try and pick the right words and even then I still pick the wrong ones.
I'm 30 mins into replying to this email for example.

 > 
 > > But often what they want isn't what they really need.
 > 
 > True.  But trying to tell them you know better than they do what they
 > need - even, or sometimes even especially, if you're right - is quite
 > often a recipe for raised hackles and a quick switch to something that
 > doesn't come across that way.
 > 
 > I am ready to listen to reasons why what I want may not be what I need.
 > But I am unlikely to listen to anyone who comes across as "I know
 > better than you do, so you should do it my way".
 > 
 > None of this is to say that that's what you're saying, nor what you
 > meapn.  But "we don't support this; even if it's what you want, we
 > think it isn't what you need" in the documentation is liable to come
 > across that way.

Ah we finally get to what you need :)
I'll quote what you said again.

 > PXE proper, no.  But (a) that was just one example of an unconfigurable
 > DHCP client and even with just PXE, (b) how would you address different
 > machines needing different kernels?

You need to be able to identify which kernel to send to a PXE client to boot.
Vendor class identifier is sent by PXE clients - could that be keyed off to pick a kernel?
Even if not, there could be a new PXE plugin to detect some magic in the VCI option, examine the hlen, hytpe and chaddr of the bootp message and add some options based on some config.

I think that people are too fixated on static config == static address and that's really not the case.
I mean I've just today written two plugins to lookup your IP by hostname or by ethernet address. That's what they want, but it's not what they need.

The absolute dream goal for me is that either the client OR the DNS server is the source of truth for hostname <-> ip address mapping.
DHCP plays a part sure but it's more of a middleman, not a source of truth.
If it was a source of truth for addresses, we would not need to perform Duplicate Address Detection on offered addresses.

I have a ton of devices I have zero control over, can't be customised and yet I only have one box, my main router, with a fixed IP.
The IP's of my other devices change from time to time, but it's not really important as every box I need to manualy connect to can be reached by mDNS or DDNS.

Roy