[ipxe-devel] custom dhcp client_id option

Hummel Frank F.Hummel at ads-tec.de
Wed Apr 13 07:15:57 UTC 2016

Please have a look at this: http://www.intel.com/content/www/us/en/support/software/manageability-products/000007129.html

The problem arises if you work in a production environment where you set up completely new systems.
Start condition is:
- MAC addresses programmed
- System UUID not yet programmed or set to e.g. 0000-0000-..... (same on all systems)

Now imagine, you have some dozens of systems that simultaneously PXE-boot to get their system UUID assigned and programmed by the central server and the systems are all identified by their UUID instead of the MAC.
This results in all systems getting the same IP from the DHCP server and therefor stops your production.
We ran into that problem and had to update the option ROM because of that.

mit freundlichen Grüßen
with kind regards

i. A. Dipl.Ing. (FH) Frank Hummel
System development

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-----Ursprüngliche Nachricht-----
Von: ipxe-devel-bounces at lists.ipxe.org [mailto:ipxe-devel-bounces at lists.ipxe.org] Im Auftrag von Michael Brown
Gesendet: Dienstag, 12. April 2016 23:19
An: Maule Mark; ipxe-devel at lists.ipxe.org; Wissam Shoukair
Betreff: Re: [ipxe-devel] custom dhcp client_id option

On 12/04/16 17:08, Maule Mark wrote:
> Yea, they use client-identifier a lot, but I don't see that they ever 
> say what the id should be, only that it is unique on the subnet.  
> Since in the general case a system might want to have independent 
> ipaddr's from the same subnet assigned to dhcp clients running 
> per-port, wouldn't that mean we need in general for the client id to 
> be unique per port (with the ability to override in special case instances)?

Some DHCP identifiers are intended to be unique to the machine, rather than unique to the network interface.  It's unclear (to me) which is intended by the RFC.

> On a separate note, is it even required that the client identifier for 
> the purposes of address assignment come from DHCP option 61?  The pxe 
> spec seems to use the ambiguous "DHCP option tags" terminology, 
> implying that maybe it is the dhcp server that should be configurable.

Section 2.3 (page 21) of the PXE spec states:

   The Client UUID field specifies a universally unique ID (UUID), retrieved
   from the client system.  The client must have a UUID and must report it in
   tag #97 and #61.

so the PXE spec does require that we put the (SMBIOS) UUID into DHCP option 61.  There's nothing in the PXE spec that requires the DHCP server to use option 61 for the purposes of address assignment, however.

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