Re: duplicate MAC - Re: 13.1R problems on Pi3

On 2022-Jul-5, at 16:37, Karl Denninger <karl@denninger.net> wrote:

> On 7/5/2022 19:34, bob prohaska wrote:
>> On Tue, Jul 05, 2022 at 07:02:18AM -0700, Mark Millard wrote:
>> 
>> 
>>>> So for you I would guess:
>>>> 
>>>> ifconfig_ue0="ether ??:??:??:??:??:?? inet 50.1.20.28 netmask 255.255.255.0"
>>>> 
>>  
>> I tried a few variants, all produced a dead connection. 
>> 
>> Using  one like you suggested:
>> 
>> # ethernet address increased by 1 in the last digit
>> ifconfig ue0="ether b8:27:eb:71:46:4f inet 50.1.20.28 netmask 255.255.255.0"
>> 
>> produced a flood of errors during boot:
>> ifconfig: interface ue0=ether b8:27:eb:71:46:4f inet 50.1.20.28 netmask 255.255.255.0 does not exist
>> 
>> There was clearly no network connectivity, but the serial console
>> remained responsive. The host sharing the same MAC address exhibited
>> no connectivity problems. 
>> 
>> 
>> Another suggestion was found in an old forum post, assigning the IP
>> in the usual fashion but adding an alias:
>> 
>> ifconfig_ue0="inet 50.1.20.28 netmask 255.255.255.0" 
>> ifconfig_ue0_alias0="link b8:27:eb:71:46:4f"
>> (trading ether for link had no effect)
>> 
>> resulted in the gateway (and everything else) being unreachable. 
>> 
>> Thanks for writing!
>> 
>> bob prohaska
>> 
> Crap - you have to see if you can get u-boot (e.g. in config.txt) to do it then....

config.txt is for the RPi* firmware. I've sent notes
about doing this earlier.

U-Boot is not part of the RPi* firmware, it is an optional,
separate addition. (An alternative is EDK2 UEFI/ACPI
software.) FreeBSD choose to use U-Boot instead of
EDK2. Some linux based distributions do not use either.
But all use some vintage of RPI* firmware.

> that's not supposed to happen (manufacturing two devices with the same MAC address) and is EXTREMELY not-nice for the very reason you've discovered.

Bob P. has not reported on what a RaspiOS reports
for:

# vcgencmd otp_dump

Parts of the output should be interesting relative
to the duplication if he can generate and capture
the output.

> Linux's boot line has an override available for it, so there IS a way.

Quoting a prior message that avoid even boot line use:
I've found references to an undocumented control in config.txt :

force_mac_address=??:??:??:??:??:??

See, for example, https://forums.raspberrypi.com/viewtopic.php?t=327562

Apparently, force_mac_address controls what value shows up in
the device tree for what the ethernet0 alias points to in the
device tree.

Note that having a odd .dtb file could lead to force_mac_address
not working. (The RPi* firmware reads the file and then makes
a device tree with some modifications applied.)
END QUOTE

While the official documentation does  not cover it, RPi*
engineers talk about it on the forums at times when supporting
people with problems.


===
Mark Millard
marklmi at yahoo.com