Andrew Brown wrote:
> 
> >> i was thinking of the link layer address.  there's currently no way to
> >> get that from the network layer in the kernel on a per-packet basis,
> >> unlike, say, the receiving ip address.
> >
> >What makes you think the link layer address is unique?
> 
> because it has to be?

You don't believe the standards do you?
You can use 'locally administered' addresses (eg x2:xx:xx:xx:xx:xx)
provided
you ensure they are unique to your lan segment.  If you run DecNet you
HAVE
to use locally administered addresses.
Interesting some cards come with such addresses!
> 
> >It only needs to be unique on a (bridged) LAN segment.
> 
> there, like that.
> 
> >Indeed some of the sBus ethernet cards sold by sun do not have a MAC
> >address PROM.  The solaris driver (and I assume the netbsd one) uses
> >the system mac address for these add-on cards.
> 
> sure, i knew that.  suns (by default) take the top three octets of the
> mac address from the prefix assigned to them by sun, who gets it from
> iee, i suppose) and the bottom three from the hostid and use the same
> mac address on each physical interface.  typically, there should be no
> reason not to.  in practice, however, i don't like it, so i set this:
> 
>         local-mac-address?=true
> 
> and it uses the mac address from the interface, not the constructed
> one.

No - it can only do that if your card has a MAC address.
I'm sure that some of the sun cards don't have one - certainly they
don't have an address in the place where you would expect it to be.
Was a long time ago, don't know if we searched through the fcode worms.

IP will work fine provided you don't enable IP_FORWARDING on hosts
that share mac addresses !

	David