[ipxe-devel] Change cached DHCP responses possible using set?

Michael Brown mcb30 at ipxe.org
Wed Feb 26 17:43:47 UTC 2014

On 26/02/14 14:23, Andreas Buschka wrote:
> To fix this problem, I need to be able to modify the cached DHCP response packet (in my scenario, there is no proxy DHCP server involved). In SYSLINUX, there is a module called pxechn.c32, which is able to do exactly that (see the description on http://www.syslinux.org/wiki/index.php/Pxechn.c32 for details). However, since this SYSLINUX module does not work on EFI, I cannot use it to solve my problem.
> So, my question is: Is there a feature in iPXE (UEFI version) that would allow me to change parts of the cached DHCP response like “boot file name” so that bootmgfw.efi uses the correct file names?

With the BIOS version of iPXE, you can use the "set" command to modify 
the stored DHCP parameters before loading an external PXE NBP.  The NBP 
uses the PXE API provided by iPXE to retrieve the DHCP packet, which 
iPXE constructs on the fly.

Unless I'm missing something, the UEFI version of iPXE provides no 
equivalent way for the booted program to obtain the DHCP information.  I 
think bootmgfw.efi is accessing the EFI_DHCP4_PROTOCOL provided by the 
platform's builtin DHCPv4 driver.

iPXE could potentially expose its own EFI_DHCP4_PROTOCOL, but this would 
be a non-trivial amount of work.


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