[klibc] ipconfig and boot filename option

Άλκης Γεωργόπουλος alkisg at gmail.com
Mon May 26 00:26:57 PDT 2008

I guess I need to explain the big picture here, maybe I'm not
describing the problem well or maybe I'm missing an obvious solution.

In a typical school ltsp environment, we have a switch in which there
are connected:
* An adsl router with a dhcp server and with a pool of e.g. -
* An ltsp server with a static address of and a (second)
dhcp server with a pool of -
(ignore some details, the ltsp server has a second card 192.168.1.x to
reach the router)
* A dozen PCs which are supposed to boot from the ltsp server and
become ltsp clients.
* Some other, Windows PCs which are supposed to get an ip address from
the router.

We cannot have 1 dhcp server, because the router can't give boot
information, and the ltsp server is not always online, so the Windows
PCs should be able to get their address from the router.
We don't want to buy extra hardware, like another switch, we'd prefer
a software solution so that it can be deployed in hundreds of schools
with minimum cost.
We don't want to use static IPs, because a teacher with a laptop might
want to use the internet.

Typical boot sequence for ltsp clients:
1) They boot using pxe, so they definitely get a correct address from
the ltsp server, since the router doesn't give a boot file name.
2) They load initramfs and then they call ipconfig for a second dhcp request.

At this stage there is the problem, the ltsp clients might get an ip
from the router so they can't complete the booting process (contact
the ltsp server and use either nbd/squashfs or nfs file system).

> Seriously speaking, this is really messy.  You need to consider not just how
> this will affect ipconfig, but how it will affect whatever DHCP client you
> are using that is actually respecting the DHCP lease times, renewing your
> lease, etc.

I really don't get this, you may shoot me. The dhcp server (of the
ltsp server) which hands over the ip addresses is only responsible for
these dozen clients and is on a different, private subnet. How can
there be problems with lease times?

I'm not an ltsp developer, I'm a school teacher who bumped into a
problem. The best solution that I've found so far and that I can
actually implement is to modify the ltsp boot script so that it calls
ipconfig -c bootp.
If anyone can see a better solution that doesn't involve writing
custom software, I'll be glad to hear it.

Thanks for your time,

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