[ipxe-devel] custom dhcp client_id option

Michael Brown mcb30 at ipxe.org
Tue Apr 12 21:19:24 UTC 2016

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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