[ipxe-devel] keep-san - skip-san dhcp options

[Michael Brown]

On Friday 04 Feb 2011 13:13:33 Paul Geraedts wrote:
> Recently I came across iPXE and yesterday I tried it. It has added
> some nice features to gPXE!
> 
> What is the exact syntax of the dhcp-options related to keep-san and
> skip-san? I know that:
>   dhcp-option=175,8:1:1 # keep-san=on (and skip-san=off?)
> 
> But how to set the 3 other combinations of keep-san and skip-san? E.g.
> what is the exact meaning of the :1:1 part?

Option 175 is an encapsulated option field.  That "175,8:1:1" breaks down to:

  option 175 contains:
     option 8, length 1, value 1

i.e. option 175.8 (DHCP_EB_KEEP_SAN) has value 1.  You can see this from the 
iPXE command prompt using

  show 175.8:hex

which should show

  175.8:hex = 01

The instructions for ISC dhcpd (http://ipxe.org/howto/dhcpd) show that skip-
san-boot is sub-option 9:

  option ipxe.skip-san-boot code 9 = unsigned integer 8;

so for your (dnsmasq?) syntax, you would need to use

  dhcp-option=175,9:1:1

You can concatenate multiple options within option 175: to specify both skip-
san-boot and keep-san, you would use

  dhcp-option=175,8:1:1:9:1:1

If you're doing anything remotely sophisticated with iPXE options, you may find 
it easier to use ISC dhcpd instead, since this allows you to use syntax such 
as:

  option ipxe.keep-san 1;
  option ipxe.skip-san-boot 1;

which is easier to read and maintain.

Michael