[plug] using several ethernet cards problem...

Anthony Woods anthony at monkey.id.au
Fri Jan 4 15:32:37 WST 2008

On Fri, 2008-01-04 at 14:35 +0900, Marcos Raul Carot Collins wrote:
> El Thu, 3 Jan 2008 10:54:20 pm Ian Kent escribió:
> > On Thu, 2008-01-03 at 22:16 +0900, Richard Meyer wrote:
> > > Maybe not.
> > >
> > > This is the way I see it, and I MAY be wrong, but ...
> > >
> > > You've got a computer w/ 4 interfaces, which means 4 IP addresses.
> >
> > How does your server know what interface to send a reply to if they are
> > all on the same network!
> >
> > Setup a bonded interface or subnet.
> >
> > Ian
> Sorry Ian, but I don't know what you mean.
> My guess is that you tell me that each ethernet card has to be in a different 
> subnet?
> Can't it be done without doing it?
> Also, is it possible to build a "virtual" ethernet card with the four? I mean 
> all having the same IP, and behaving as if it were one.
> Thank you!
> Marcos
> _______________________________________________

You cant have the 4 different interfaces all servicing the same subnet.
Your PC makes routing decisions based on destination IP, your routing
table will have 4 routes for the subnet and will pick the one with the
highest priority, though that may not be the interface that the host is
connected to. Your PC is most likely using the onboard interface as the
preferred route, hence why PC's plugged into that port work.

It is possible to build a virtual ethernet card, it is called a bonded
interface, as Ian has already pointed out. This should work for you. see
http://www.linuxhorizon.ro/bonding.html for more details. I think that
mode 3 will probably be best for you.  
Though i still think that using subnets is a much better solution.
Using subnets will also allow all of the PCs to talk to each other (if
you enable ip_forwarding on the computer with the 4 interfaces.)


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