option 67 boot-file-name FF00 at the end of the data string

[Jan-Philipp Snizek]

Hi Darren

Thanks for pointing in the right direction.

For everyone else digging into PXE Boot with Windows Deployment Server in a Microsoft Configuration Manager and Kea DHCP server environment, this is the solution that seems to work for both, older and newer (Lenovo) laptops.


                {

                        "name": "boot-file-name",

                        "csv-format": false,

                        "data": "53 4d 53 42 6f 6f 74 5c 78 36 34 5c 77 64 73 6d 67 66 77 2e 65 66 69 00 ff"

                },

where the last to bytes 00 ff are the string termination sequence.

Everything preceeding that is converted to SMSBoot\\x64\\wdsmgfw.efi

I wonder if there could be a more Administrator friendly way in Kea DHCP to configure this.


Best,
Philipp


From: dhcp-users <dhcp-users-bounces at lists.isc.org> on behalf of Darren Ankney <darren.ankney at gmail.com>
Date: Tuesday, 7 May 2024 at 08:51
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: Re: option 67 boot-file-name FF00 at the end of the data string
Hi Philipp,

You would need to specify the entire string in hex instead as noted in
the ARM: https://kea.readthedocs.io/en/kea-2.4.1/arm/dhcp4-srv.html#standard-dhcpv4-options

---
Kea supports the following formats when specifying hexadecimal data:

Delimited octets - one or more octets separated by either colons or
spaces (":" or " "). While each octet may contain one or two digits,
we strongly recommend always using two digits. Valid examples are
"ab:cd:ef" and "ab cd ef".

String of digits - a continuous string of hexadecimal digits with or
without a "0x" prefix. Valid examples are "0xabcdef" and "abcdef".
---

There is also an example of doing this there:

---
"Dhcp4": {
    "option-data": [
        {
            "name": "domain-name-servers",
            "code": 6,
            "space": "dhcp4",
            "csv-format": false,
            "data": "C0 00 03 01 C0 00 03 02"
        },
        ...
    ],
    ...
}
---

Thank you,
Darren Ankney

On Fri, Apr 26, 2024 at 4:52 AM Jan-Philipp Snizek
<jan-philipp.snizek at business.uzh.ch> wrote:
>
> Hi
>
> In isc-dhcpd I use as option 67 option bootfile-name "SMSBoot\\x64\\wdsmgfw.efi\000";
> This works with any uefi bios, older or new.
>
> How do I do the end of string sequence \000 in kea-dhcp4?
>
> There seem to be older uefi BIOSes that upon receiving the option 67 string, they attach FF00 at the end of the string and then try to load the efi file. This ends with the ftfp server returning 'file not found'.
> How do I have to do this end-of-file sequence in Kea-dhcp4? Is that even the correct name for this? I'm not sure, I usually don't play with these lower level things.
>
> For reference, here's the relevant part of the kea-dhcp4 config file that works with recent uefi bioses:
>
>     "client-classes": [
>        {
>             "name": "pxeclientx64",
>             "test": "option[60].text == 'PXEClient:Arch:00007:UNDI:003016'",
>             "option-data": [
>                 { "name": "boot-file-name", "data": "SMSBoot\\x64\\wdsmgfw.efi" },
>                 { "name": "tftp-server-name", "code": 66, "data": "tftp-server.mydomain.local" }
>            ]
>        }
>     ],
>
> Thanks,
>
> --
>
>   Philipp
> --
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