[U-Boot] DHCP Command Does Not Populate all DHCP Options supplied by DHCP Server

[U-Boot] DHCP Command Does Not Populate all DHCP Options supplied by DHCP Server

[dh at synoia.com]

The u-boot DHCP Command appears to populate some DHCP options, for example: rootpath and gateway, netamsk and ipaddress. It does not appear to populate Bootfile Name (Option 67) and Boot Server Host Name (Option 66)

Can populating all option returned from DHCP. BOOTP etc be added?

I can (possibly) write the code, but an not that skilled, nor do I have much understanding of the u-boot code review and approval process.
?Duncan Hare

714 931 7952

[U-Boot] DHCP Command Does Not Populate all DHCP Options supplied by DHCP Server

[Stefan Bruens]

On Samstag, 4. Februar 2017 18:38:38 CET dh at synoia.com wrote:
> The u-boot DHCP Command appears to populate some DHCP options, for example:
> rootpath and gateway, netamsk and ipaddress. It does not appear to populate
> Bootfile Name (Option 67) and Boot Server Host Name (Option 66)
> 
> Can populating all option returned from DHCP. BOOTP etc be added?
> 
> I can (possibly) write the code, but an not that skilled, nor do I have much
> understanding of the u-boot code review and approval process. Duncan Hare

Unfortunately you are not stating which messages you are referring to, I 
assume you refer to DHCPDISCOVER and DHCPREQUEST.

DHCP is an extension to BOOTP, but there are some points where DHCP deviates 
from BOOTP behaviour. One such point are the sname and file fields. While in 
BOOTP these are used to select a specific server/image to boot, in DHCP these 
are no longer used as such in the DHCPDISCOVER/REQUEST messages. The server/
file are selected by the DHCP server based on e.g. MAC address, client 
identifier or any other option.

RFC2131, page 37 [1] states for both sname/file, DISCOVER/REQUEST:

"options, if indicated in 'sname/file' option; otherwise unused"

Option 67 and 66 are only relevant in OFFER/ACK messages.

Kind regards,

Stefan


[1] https://tools.ietf.org/html/rfc2131#page-37


-- 
Stefan Br?ns  /  Bergstra?e 21  /  52062 Aachen
home: +49 241 53809034     mobile: +49 151 50412019
work: +49 2405 49936-424

[U-Boot] DHCP Command Does Not Populate all DHCP Options supplied by DHCP Server

[Stefan Bruens]

On Samstag, 4. Februar 2017 20:16:20 CET dh at synoia.com wrote:
> Stefan
> Thanks for the reply
> I suspect it is the offer response to the DHCP u-boot command.
> 
> Options 66/67 are important in the netboot scenario.
> 
> Regards Duncan Hare

Dear Duncan,

it would be good if you were more specific in your messages. Scenario, DHCP 
server, what do you want to achieve. You should also tell what you are 
referring to - messages on the wire, u-boot environment variables, ... Please 
be terse in your questions, but also give *all* necessary information. If in 
doubt, there is seldom to much information.

Of course bootserver and image url are typically [2] required for netboot 
scenarios. Although Option 66/67 is one possibility to specify this 
information, the "traditional"/non-PXE method of specifying these values is 
using the siaddr/sname/file fields. U-Boot currently evaluates siaddr and the 
file field. The sname field is ignored, as it would eventually require DNS 
resolution.

It is the obligation of the DHCP server to set these fields. The DHCP client 
*must not* use the sname/file fields in its DISCOVER/REQUEST (but for option 
overloading).

Specifically which information the DHCP *should* give to the client is 
specified in the DHCP Parameter Request List option (55). As u-boot uses 
siaddr/file for the bootstrapping, it omits the options 66/67. *If* a DHCP 
server sends out option 67 (bootfile name) although not requested, u-boot 
prefers its value over the file field.

Kind regards,

Stefan

[2] both values can be pre-set in the u-boot environment

-- 
Stefan Br?ns  /  Bergstra?e 21  /  52062 Aachen
home: +49 241 53809034     mobile: +49 151 50412019
work: +49 2405 49936-424