Trying to understand isc-dhcpd log ...

I try to understand something about "vendor" in the isc-dhcp server... My main computer act a a dhcp/tftp server for my spares.

I added
log(info, concat("vendor-class-identifier = ", option vendor-class-identifier));
log(info, concat("vendor-string ", vendor-string));
to dhcpd.conf.

The "spare" is my toy, with a multiboot Win XP / Linux Mint /Linux CNC/ FreeBSD / NetBSD (no Haiku yet, and I lost my BeOS 4.5 genuine cd ... :) )

When it boots with PXE, I see "PXE-xxxxx" in /var/db/dhcpd/dhcpd.leases.

Booting NetBSD gives "NetBSD-7.0.1:i386:i386".
Booting Win XP gives "MSFT 5.0"

But when the toy boots on Linux Debian or FreeBSD, there's no info ..

This computer as a multiboot Linux Mint/FreeBSD, but same behavior with Linux (in /var/syslog).

Did I miss something ?
Sorry, I've been using *BSD for years, but I'm a noob.