[syslinux] syslinux.efi and vendor-class-identifier

James Pearson james-p at moving-picture.com
Thu Nov 21 06:21:44 PST 2019

H. Peter Anvin wrote:
>> Watching the dhcp/tftp traffic via wireshark, I see the initial DHCP
>> Discover, Offer, Request and ACK, followed by the tftp download of
>> syslinux.efi - and then the client sends another DHCP Discover request,
>> gets no reply - and repeats the DHCP Discover request 3 more times and
>> then gives up.
>> I believe the issue is that the 2nd set of DHCP Discover requests don't
>> include a 'vendor-class-identifier' - so our dhcpd config ignores the
>> request?
>> ...
> DHCP is executed by firmware, not Syslinux, so either file a bug report
> with your vendor or you have to change your configuration.
>  From reading RFC 2131, your configuration is wrong. RFC 2131 explicitly
> states the vendor class identifier is optional (table 3, page 28.)

I did contact Dell about this - but never heard anything back ... and 
I'm not holding my breath waiting for anything to come of it :-)

I've worked around this now, but I'm still puzzled as to why a Dell 3930 
workstation starts a second DHCP Discover transaction after 
'syslinux.efi' has been download, whereas a Dell Latitude 7480 doesn't

I accept that Dell probably have different UEFI firmware for different 
types of hardware - which may be the reason for this different behaviour ?

However, if I set up UEFI booting of grub for the (same) Dell 3930, then 
the file 'shim.efi' is initially downloaded followed by the file 
'grubx64.efi' - but this time, without a second DHCP Discover 
transaction after the first downloaded file

So, hence my query of, is 'syslinux.efi' doing anything that might 
somehow trigger (in some cases) a 2nd DHCP Discover before it attempts 
to download 'ldlinux.e64' ? - i.e just wondering what might be different 
in the way 'shim.efi' is loaded/executed that doesn't trigger this 2nd 
DHCP Discover?

That said, I know very little of how the UEFI firmware interacts with 
what gets downloaded and executed (and vice versa) - so I might very 
well be completely off track ... but still puzzled :-)


James Pearson

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