[U-Boot] u-boot soft and hard ethernet addresses
Date: Tue, 14 Nov 2017 10:31:56 +0100 From: Mike Looijmans mike.looijmans@topic.nl To: Wolfgang Denk wd@denx.de, Prabhakar Kushwaha prabhakar.kushwaha@nxp.com Cc: "u-boot@lists.denx.de" u-boot@lists.denx.de, "joe.hershberger@ni.com" joe.hershberger@ni.com Subject: Re: [U-Boot] ethernet: ROM MAC address vs env variable MAC address Message-ID: 45c912c9-ce5a-4ee0-326a-e1dadce04b65@topic.nl Content-Type: text/plain; charset="utf-8"; format=flowed
On 13-11-17 20:49, Wolfgang Denk wrote:
Dear Prabhakar,
In message HE1PR04MB12410876E4BA09FC9CD7800C97560@HE1PR04MB1241.eurprd04.prod.outlook.com you wrote:
Why ROM MAC address getting overwritten by environment env MAC address.
Because in U-Boot we give the user the freedom to do what he needs/wants to do. Usually the environment value gets initialized from the value in the ROM, so there is no difference anyway. But if the user wants a specific setting, he can change it.
MAC address is something unique and assigned to a particular device. So one should never change its MAC address.
U-Boot follows good old UNIX style here:
"UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things." - Doug Gwyn
Many board manufacturers "assign" this unique MAC address by printing it on a sticker and sticking that on the board somewhere. It's pretty darn hard to read a printed sticker in software, so we have to revert to solutions that actually work.
In the "clever things" department, protocols like IPv6 merrily broadcast your MAC address across gateways on the big bad internet, so if you value your privacy, you'll appreciate the possibility to change your MAC address at will.
Kind regards,
Mike Looijmans System Expert
TOPIC Products Materiaalweg 4, NL-5681 RJ Best Postbus 440, NL-5680 AK Best Telefoon: +31 (0) 499 33 69 79 E-mail: mike.looijmans@topicproducts.com Website: www.topicproducts.com
Please consider the environment before printing this e-mail
P to get the real hardware address used delete the variable ethaddr before saving the environment. This forces the board code the load the actual hardware address, if there is one, into the environment at start time. Otherwise you will always boot with the Ethernet address from the first time the environment was saved.
Which make the environment not portable to multiple boards.
Duncan Hare
714 931 7952
Dear Duncan,
In message 1814106598.1047276.1510787951141@mail.yahoo.com you wrote:
Many board manufacturers "assign" this unique MAC address by printing it on a sticker and sticking that on the board somewhere. It's pretty darn hard to read a printed sticker in software, so we have to revert to solutions that actually work.
Such solutions usually include a barcode reader attached to some PC which is used when you commission the board. And yes, in this case it is mandatory that the MAC address(es) stored in the environment (which gets initialized as part of the aforementioned commissioning procedure) takes precedence over any MAC address(es) that might be stored somewhere in the hardware.
In the "clever things" department, protocols like IPv6 merrily broadcast your MAC address across gateways on the big bad internet, so if you value your privacy, you'll appreciate the possibility to change your MAC address at will.
Right, this is another of a list of reasons why changing the MAC address makes a lot of sense.
Best regards,
Wolfgang Denk
participants (2)
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Duncan Hare -
Wolfgang Denk