[Dnsmasq-discuss] Boot file name not given (DHCP Option: 67 Bootfile name - is set but not used in PXE clients)

[Oliver Freyermuth]

Hi,

Am 08.03.21 um 00:42 schrieb Christoph Loesch:
> Hi,
> 
> with dnsmasq (version 2.80 on current OpenWRT 19.07.7) I noticed following (in my opinion wrong) behaviour:
> 
> when using the setting "dhcp-boot=/pxelinux.0,servername,192.168.1.123" the DHCP Offer/ACK packets sent do not contain the "Boot file name" in the header but "Option: (67) Bootfile name" is set.

it's not "wrong" in my opinion, however, there are still many legacy / broken clients out there which don't conform to the DHCP standard completely,
and only check the classic BOOTP headers. A noteworthy quite recent example is Grub2, which only learnt this in 2019:
  https://github.com/rhboot/grub2/commit/93289dc67c7e213b21df0eb09afea5e3b00ad7df#diff-93cd75cf8712d66c15ae5885f7cac5dae3531aaef211a17ef9885eb443ecdb0b

> Some DHCP clients, who read Option 67 can work with that, but some clients like PXE do not read that option therefor are failing for first tftp file rrq.
> 
> As I could not find a git commit regarding a fix for this, I wanted to ask if someone can confirm (and/or possibly fix) this on recent dnsmasq version?

I also have such legacy clients in use. The option "dhcp-no-override" forces dnsmasq to use the classic BOOTP headers.
Note that in general, using the dedicated options for servername and filename is preferrable, since it allows to reuse the space in the headers for options,
but if you have legacy clients (as we also have) you have to set "dhcp-no-override".

Does this also solve your issue?

Cheers,
	Oliver

> 
> Kind regards,
> Christoph
> 
> 
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