> > For a router or firewall, you really, really want to have all
> > interfaces running on add-in NICs, so that you can avoid this
> > problem.
> 
> Which problem?  High interrupt load due to poor interface buffering?

There isn't an interrupt problem, one interrupt per rx or tx packet.
(A shame that you can't disable the 'end of tx' interrupt - we got
a significant increase in throughput with the pcnet-isa, pcnet-pci
and FEPS by only enabling the end of tx interrupt when the tx side
was lan limited...)

> Isn't a dedicated router box just where you _don't_ care about that?
> My main house LAN gateway box is an IPX with an addon Ethernet in each
> SBus slot (Ethernet/SCSI, but I don't normally use scsibus[12]).
> (le0 (on-board) is the main (routable) portion of the house LAN, le1 is
> the DSL, and le2 is the non-routable portion of the house LAN.)

Seems right - all things being equal the motherboard interface can handle
the higher traffic rate.

With one proviso (I've just remembered) the (nmos) 7990 lance only has a
single fifo, it cannot generate a collision on a frame that closely
follows one it received (because it isn't ready to tx until there are 64ish
bytes in the fifo) and it would have to receive the next packet.
This usually only affects bridges on VERY heavily loaded LANs
If you have a 7990 on the motherboard and a 79c90 on an sbus card and
are suffering from the inability to tx packets, then try swapping the
interfaces about - or modify the (single system) that is blasting the
LAN to limit itself to (say) 95%.

    David