On 20/08/2020 11:44, Maciej Rabeda wrote:
@Michael
I am now wondering whether bit 3 is actually relevant to server choice.
Bit 3:
== 0 -> prompt user to choose a boot file. Which means to me: show
minimal menu with prompt (tag 10 - PXE_MENU_PROMPT) and options (tag 9 -
PXE_BOOT_MENU).
== 1 -> do not prompt user. If boot file name is present (option 67),
download that boot file.
Bit 3 does not seem to specify/regulate which server to use.
Choice of server IP might look like:
if (option 43 is present, tag 6 is present, tag_6.bit_2 is set and tag 8
is present and valid)
take server IP from tag 8 (PXE_BOOT_SERVERS)
else if (option 66 is present)
take server IP from option 66 (TFTP server name)
else if (option 54 is present)
take server IP from option 54 (Server Identifier)
else
failure
RFC 2132 defines option 66 as a hostname (not an IP address): it is the
equivalent of the non-option "sname" field.
RFC 2132 defines option 54 as the DHCP server identifier, which is
unrelated to the TFTP server.
In the simple case (with no PXE menus involved), the TFTP server IP is
provided by the non-option "siaddr" field.
If option 60 is set to "PXEClient" and option 43 tag 9 is present and
option 43 tag 6 bit 3 is clear then this initiates a convoluted process
in which the user is first presented with an interactive menu
(constructed from the contents of option 43 tag 9) in order to select a
"boot server type", after which a second convoluted process is performed
to query the network using a protocol that is almost, but not quite,
entirely unlike DHCP. The TFTP server IP and boot filename are
eventually taken from the selected response packet in this final
almost-DHCP exchange.
Michael
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