[Dnsmasq-discuss] [EXTERNAL] Re: UEFI PXE Boot Issue: dhcp-option 60

Swanand Vaidya Swanand.Vaidya at veritas.com
Tue Dec 8 11:57:10 GMT 2020


Hi,



Indeed this was due to "pxe-prompt" which I was using that was causing this issue for UEFI. This worked fine for BIOS clients.

After removing pxe-prompt, dnsmasq ver. 2.76 worked successfully for PXE booting of UEFI hosts.



On the left is DHCP-ACK packet send from server without "pxe-prompt" and on the right the same packet when "pxe-prompt" is specified.

Specifying pxe-prompt made dnsmasq send dhcp options 60, 97 and 43.



[cid:image002.png at 01D6CD87.586E9710]



Thank you for your help.



-swanand



-----Original Message-----
From: Wang Shanker <shankerwangmiao at gmail.com>
Sent: Monday, December 7, 2020 8:50 PM
To: Swanand Vaidya <Swanand.Vaidya at veritas.com>
Cc: Geert Stappers <stappers at stappers.nl>; dnsmasq-discuss at lists.thekelleys.org.uk
Subject: Re: [Dnsmasq-discuss] [EXTERNAL] Re: UEFI PXE Boot Issue: dhcp-option 60



Hi,



In theory, `dhcp-pxe-vendor` cannot prevent the special handling of dhcp-option 60 when replying to pxe clients.



However, dnsmasq identifies a pxe client by matching "PXEClient"

string sent in the requests. By using this setting, you can specify a dummy string for this like DUMMY6789, and normal pxe clients won't be seen as pxe clients anymore by dnsmasq and thus the special handling of dhcp-option 60 is disabled.



As I wrote in my previous mail. I strongly suspect the `pxe-prompt` option is the cause of the problem.



Cheers,



Miao Wang



> 2020年12月07日 22:04,Swanand Vaidya <Swanand.Vaidya at veritas.com<mailto:Swanand.Vaidya at veritas.com>> 写道:

>

> Hi Geert,

>

> Yes, the source I had taken included this commit. But as I understand it allow you to send specific value for vendor class in dhcp-option 60.

> I want to totally stop dhcp-option 60 from being sent as different clients may have different requirements.

> Does the new setting 'dhcp-pxe-vendor' allow you to stop dhcp-option 60 from being sent?

>

> Thanks,

> -swanand

>

> -----Original Message-----

> From: Geert Stappers <stappers at stappers.nl<mailto:stappers at stappers.nl>>

> Sent: Monday, December 7, 2020 7:19 PM

> To: Swanand Vaidya <Swanand.Vaidya at veritas.com<mailto:Swanand.Vaidya at veritas.com>>;

> dnsmasq-discuss at lists.thekelleys.org.uk<mailto:dnsmasq-discuss at lists.thekelleys.org.uk>

> Subject: [EXTERNAL] Re: [Dnsmasq-discuss] UEFI PXE Boot Issue:

> dhcp-option 60

>

> On Mon, Dec 07, 2020 at 01:11:18PM +0000, Swanand Vaidya wrote:

>> Hi,

>>

>> I am trying to PXE boot a UEFI enabled Dell machine with dnsmasq

>> acting as both the DHCP and TFTP server.

>> The client and server perform the DHCP steps: DHCP Discover, DHCP

>> Offer, DHCP Request and DHCP Ack as expected.

>>

>> But, thereafter, the client simply aborts the protocol (it does not

>> do TFTP to download the NBP file syslinux.efi and others) and I can

>> see

>> error:

>> "PXE-E21: Remote boot canceled" on the client console.

>>

>> The same dnsmasq configuration works for booting a BIOS based machine.

>>

>> I found that dnsmasq is sending dhcp-option 60 with value as "PXEClient"

>> which is causing this issue.

>>

>> I could not find any way to disable this from being sent to the client.

>>

>> Finally, I modified the source code in rfc2131.c by adding "return"

>> statement at the top of the function pxe_misc(). The dnsmasq binary

>> so built now works fine for booting the UEFI machine.

>>

>> I would like to know:

>>

>>  1.  If this is a known issue? I tried latest 2.82 version of dnsmasq

>>      as well as building from the latest source snapshot from HEAD.

>

> Did that include http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=4ded96209e8346711f9d0b9e13a835d42835853d ?

> Yes, that is a very very fresh commit.  And it is 'PXEClient' related ...

>

>

>>  2.  Is there any way to disable dhcp-option 60 from being sent over

>>      to the client by setting some configuration param in

>>      dnsmasq.conf? We can force certain option to be sent using

>>      dhcp-option-force directive, but there is nothing for the opposite

>>      direction to "force disable" a specific DHCP option. (Setting

>>      dhcp-option = <option_number> without a value only works for

>>      certain dhcp options).

>>

>

>

>

>> Thanks,

>

> You are welcome.

>

>

>

>> -swanand

>

> Regards

> Geert Stappers

>

> P.S.

> I usually don't do "Reply to All", but I do take insults.

> --

> Silence is hard to parse

>

> _______________________________________________

> Dnsmasq-discuss mailing list

> Dnsmasq-discuss at lists.thekelleys.org.uk<mailto:Dnsmasq-discuss at lists.thekelleys.org.uk>

> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss


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