Re: ethtool documentation

From: Ryan Anderson (
Date: Tue Aug 06 2002 - 21:54:10 EST

> The EEPROM (SEEPROM) on these NICS is used to contain the startup
> configuration bits and the IEEE Station Address. This must be a
> unique number that is assigned so that there is no other such
> number in (preferably) the world, and certainly in the LAN.
> If you let a user write to this area, you will allow the user
> to destroy the connectivity on a LAN.
> If you provide an ioctl() to write new SEEPROM contents, it had
> better be disabled in code that user's (any, including root)
> can execute because, if caught, your company may lose it's IEEE
> Station Addresses and never again be allowed to configure Ethernet
> Controllers.

I think you overstate the seriousness here - it's not unheard of for
manufacturers to ship hardware with duplicate MAC addresses - a trivial
search on Google turns up Cisco as one offender:

> Because of this, there is no such thing as 'unused eeprom space' in
> the Ethernet Controllers. Be careful about putting this weapon in
> the hands of the 'public'. All you need is for one Linux Machine
> on a LAN to end up with the same IEEE Station Address as another
> on that LAN and connectivity to everything on that segment will
> stop. You do this once at an important site and Linux will get a
> very black eye.

Worse than GE?

Being able to permanently fix a screwed up card that duplicated another
card on my LAN would be nice, imo.

Of course, this assumes that IEEE Station Address == MAC address.

Ryan Anderson
  sometimes Pug Majere
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