[gPXE] How to modify the code can not get DHCP information on the2nd

[Shao Miller]

sqwbwh wrote:
> At 2010-11-05 23:13:19，"ShaoMiller"<Shao.Miller at yrdsb.edu.on.ca> wrote:
>
>     sqwbwh wrote:
>>     At 2010-11-05 22:39:05，"ShaoMiller"<Shao.Miller at yrdsb.edu.on.ca>
>>     wrote:
>>
>>>>>>         sqwbwh wrote:
>>>>>>>
>>>>>>>
>>>>>>>         How to modify the code can not get DHCP information on
>>>>>>>         the 2nd?(GPXE only used to boot the system from ISCSI)
>>>>>>>         Is to remove this step.
>>>>>>>         net0: 00:0 c:: 29:08:11:35 on UNDI-PCI02: 01.0 (OPEN)
>>>>>>>         [Link: up, TX: 0 TXE: 0 TX: 0 rxe: 0]
>>>>>>>         DHCP (net0 00:0 c: 29:08:11: d5 ).... ok
>>>>>>>         net0: 192.168.0.202/255.255.255.0
>>>>>>>
>>>>>>>
>>>>>>>         This can speed up boot speed.
>>>>>>>         Normal GPXE run to start from the boot system tftp
>>>>>>>         process takes about 8 seconds or so
>>>>>>>         If removed from the second time for DHCP information
>>>>>>>         will only need a very quick 2.5 seconds.
>>>>>>>
>>>>>         Miller, Shao wrote:
>>>>>>         You most likely want the 'use-cached' option.  It is DHCP gPXE encapsulated option number 178.  Or, you can set it in an embedded script:
>>>>>>
>>>>>>           #!gpxe
>>>>>>           set use-cached 1
>>>>>>           autoboot
>>>>>         Gene Cumm wrote:
>>>>>>
>>>>>>         What file and version are you using? It sounds as if
>>>>>>         you're using
>>>>>>         undionly.kpxe or a .pxe file. undionly.kkpxe will skip
>>>>>>         this second
>>>>>>         DHCP request but certain hardware/firmware has issues
>>>>>>         with this,
>>>>>>         assuming you trust the stability of your OEM's PXE/UNDI
>>>>>>         stack.
>>>>>>
>>>>         sqwbwh wrote:
>>>>>         Shao Miller
>>>>>
>>>>>         The method is successful.
>>>>>         Thank you
>>>>         sqwbwh wrote:
>>>>>         yes
>>>>>         thankyou Shao Miller
>>>>>         Your method is useful ：）
>>>         Miller, Shao wrote:
>>>>         You’re quite welcome, and thanks for including the list on
>>>>         your other reply. :) Have a nice day. - Shao
>>>
>>         sqwbwh wrote:
>>>         Shao Miller
>>>         1:
>>>         i use :
>>>         " set it in an embedded script:
>>>>
>>>>         #!gpxe
>>>>         set use-cached 1
>>>>         autoboot
>>>         it's good
>>>         2:
>>>         "It is DHCP gPXE encapsulated option number 178"
>>>         Specifically to ask how to use this method?
>>>         What can explain it in detail?
>>>         thank~you
>>         I enjoy using the search feature at the gPXE (Etherboot)
>>         wiki. Please see:
>>
>>         http://etherboot.org/wiki/doku.php?do=search&id=encapsulated&fulltext=Search
>>         http://etherboot.org/wiki/msdhcp
>>         http://etherboot.org/wiki/dhcpd
>>
>>     ShaoMiller
>>     Use the search function.
>>     Use hyperlinks to provide you with three options for the
>>     introduction of 178 not found.
>>     178 keyword search does not find use-cached search did not find
>>     the relevant presentation.
>>
>>     Hehe. Could you give me the answer it?. English is almost a maze
>>     for me
>>
>
>     I'm afraid that I'm not sure how to explain gPXE encapsulated
>     options any better than they are explained in the wiki. DHCP
>     option 175 should be a string of bytes. Within that byte sequence,
>     there are sub-options. 'use-cached' is sub-option 178. So your
>     DHCP option 175 could look like:
>
>     0xB2 0x01 0x01
>
>     where,
>
>     0xB2 : DHCP gPXE encapsulated option 178.
>     0x01 : The encapsulated option's value occupies 1 byte.
>     0x01 : The encapsulated option's value is 1 (true).
>
>     I do not know which DHCP service you use, so I do not know how you
>     can reconfigure your service to give PXE clients this 'use-cached'
>     option via DHCP.
>
> Shao Miller
> dhcp server is msdhcp
> Use 1781.jpg and 1782.jpg is set. Enable use-cached did not succeed
> Picture shows what can it?
Those screen-shots show a DHCP option 178, not a DHCP gPXE encapsulated
option 178.

You need DHCP option 175. _Inside_ option 175, you need to have gPXE
encapsulated option 178. See:

http://etherboot.org/wiki/msdhcp#setting_up_a_gpxe_encapsulated_options_on_windows_dhcp

It shows exactly how to create the DHCP gPXE encapsulated options. 175
is a _container_. 178 ('use-cached') goes inside that container. Change
to option 175 and you will be fine, since your bytes are exactly as I
explained above: Option 178, 1 byte long, value 1. All gPXE encapsulated
options go inside option 175. 0xB2 means 178.

Please remember to carbon-copy the list using Reply-All.

- Shao Miller
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