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Diffstat (limited to 'en/preparing')
| -rw-r--r-- | en/preparing/bios-setup/arm.xml | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/en/preparing/bios-setup/arm.xml b/en/preparing/bios-setup/arm.xml index 24c2a0818..0db9a1ce2 100644 --- a/en/preparing/bios-setup/arm.xml +++ b/en/preparing/bios-setup/arm.xml @@ -27,3 +27,44 @@ product-independend instructions for ARM-based systems. </para> </sect2> + + <sect2 arch="arm" id="uboot-macsetting"> + <title>Setting the ethernet MAC address in u-boot</title> + <para> + The MAC address of every ethernet interface should normally be + globally unique, and it technically has to be unique within its + ethernet broadcast domain. To achieve this, the manufacturer usually + allocates a block of MAC addresses from a centrally-administered + pool (for which a fee has to be paid) and preconfigures one of these + addresses on each item sold. + </para> + <para> + In the case of development boards, sometimes the manufacturer wants to + avoid paying these fees and therefore provides no globally unique + addresses. In these cases the users themselves have to define MAC + addresses for their systems. When no MAC address is defined for an + ethernet interface, some network drivers generate a random MAC address + that can change on every boot, and if this happens, network access + would be possible even when the user has not manually set an address, + but e.g. assigning semi-static IP addresses by DHCP based on the MAC + address of the requesting client would obviously not work reliably. + </para> + <para> + To avoid conflicts with existing officially-assigned MAC addresses, + there is an address pool which is reserved for so-called + <quote>locally administered</quote> addresses. It is defined by + the value of two specific bits in the first byte of the address (the + article "MAC address" in the English language Wikipedia gives a + good explanation). In practice this means that e.g. any address starting + with hexadecimal ca (such as caffee123456) can be used as a locally + administered address. + </para> + <para> + On systems using u-boot as system firmware, the ethernet MAC address + is placed in the <quote>ethaddr</quote> environment variable. + It can be checked at the u-boot command prompt with the command + <quote>printenv ethaddr</quote> and can be set with the command + <quote>setenv ethaddr caffee123456</quote>. After setting the value, + the command <quote>saveenv</quote> makes the assignment permanent. + </para> + </sect2> |