Re: ifconfig change MAC address

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> Is there any reason why "ifconfig" doesn't implement any options on
> changing MAC addresses?

I think this is part history, part hardware incapability, and part lack
of generality.

> Did anybody try to patch "ifconfig" in order to add that
> functionality?

That wouldn't be enough; you'd have to add the capability to all the
Ethernet drivers as well.

I think the original basis for the resstriction is that some hardware
can't change its MAC.  While I suspect such hardware is exceedingly
rare these days - even on ports able to connect to the hardware,
soft-MAC hardware is probably more common - I don't see any reason
drivers for such hardware couldn't refuse the change.

The workaround you mention (in text I cut) amounts to putting the
hardware in promiscuous mode and doing MAC address filtering in host
software.  While this works, it is comparatively inefficient; Ethernet
interfaces normally filter on MAC addresses in hardware for a reason.
Worse, the additional expense is least affordable on the ports that are
most likely to have hard-MAC interfaces, such as vax.

Another, minor, reason is that not all network interfaces are
Ethernets, and it's not clear what should happen for interfaces not
sufficiently similar to Ethernet to use MACs.  (Given the stuff that's
already been shoehorned into ifconfig that belongs elsewhere, such as
vlan and ssid, this carries comparatively little force - that's why I
call it a "minor" reason - but not no force; having made a mistake N
times does not mean the N+1st instance isn't still a mistake.)

/~\ The ASCII                             Mouse
\ / Ribbon Campaign
 X  Against HTML                mouse%rodents-montreal.org@localhost
/ \ Email!           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B