[syslinux] pxelinux magic options 208

[Gene Cumm]

On Sun, Nov 7, 2010 at 16:11, Daniel Feenberg <feenberg at nber.org> wrote:
> On Wed, 3 Nov 2010, Jeffrey Hutzelman wrote:
>> --On Wednesday, November 03, 2010 06:18:52 PM -0400 Daniel Feenberg
>> <feenberg at nber.org> wrote:
>>> I have 2 groups of machines, and within each group the pxelinux menu
>>> configuration is standard. It would be great to have 2 configuration
>>> files rather than one for each machine.
>>>
> ...
>>
>> It works fine, but you failed to copy the block above which defines the
>> "pxelinux" option space.  Without that, the DHCP server doesn't know what
>> you're talking about.
>>
>
> OK, thanks, I am unable to find any documentation for declaring option
> spaces in the ISC dhcpd README, RELNOTES or man page, but they are mentioned
> as being supported since version 3.  The various RFCs do not specify syntax
> for the ISC dhcpd.conf file. But following the wiki example I added to
> dhcpd.conf:
>
>  option space pxelinux;
>  option pxelinux.configfile code 209 = text;
>
> as global options and then for each client:
>
>  option pxelinux.configfile "bsddefault";
>
> On rebooting the client it reports that the configuration file name is
> "pxelinux.cfg/default" and not what I want - "pxelinux.cfg/bsddefault".
>
> Any idea what I am missing?

http://syslinux.zytor.com/wiki/index.php/PXELINUX#Can_I_send_information_to_PXELINUX_via_special_options_in_the_DHCP_response.3F

Look at the part about dhcp-parameter-request-list and the code
section just above that point on the wiki page for some information
about specifying it in vendor space and forcibly returning that
option.

Also, try a packet capture.  More than likely, you'll see that your
server is not returning option 209 as most DHCP servers don't return
options that are not requested.

-- 
-Gene