On Sun, Dec 01, 2002 at 03:58:19PM +1000, Ray Phillips wrote:
> Is it possible to increase a machine's network bandwidth by 
> installing two (or more network cards) which all have IP numbers in 
> the same subnet? 

Not really.  If they're going to have different IP addresses, you
will have to do some client-based load sharing between them anyway.
At that point, if you can manage to put them on different subnets,
it will work - though you'll need to arrange your routing table so
that replies to clients take different outbound interfaces too.

> (Perhaps they might all have to have the same number?)

This won't work either.  What you're looking for here is called
EtherChannel (or FastEtherChannel) where, with the cooperation of
the switch, 2 or 4 ports are "bundled" together as a single logical
interface.  Packets are distributed between the interfaces based
on a hash of the mac addresses. NetBSD doesn't have FEC support,
but it probably wouldn't be too hard to add, using drivers like
bridge(4) as a model.

This used to be quite common for servers onto a lan of many clients,
but is generally done with GigE instead these days. I haven't yet
seen the equivalent bundling for Gig-E ports.

--
Dan.