[PLUG] which NIC is which

[J Henshaw]

----- Original Message -----
From: "Derek Loree" <derek at infotects.com>
To: <plug at lists.pdxlinux.org>
Sent: Tuesday, July 09, 2002 9:26 PM
Subject: Re: [PLUG] which NIC is which


> On Tue, 2002-07-09 at 13:45, John Telford wrote:
> > I'm building routers.  It's difficult to tell in advance which NIC will
> > be assigned eth0 and which will assigned eth1 when using two NICs.  Ping
> > testing usually clears up the identification problem.
> >
> > The identification problem gets worse when adding a third NIC, after
> > sorting out the first two NICs.  Frequently the eth0 or eth1 assignment
> > for the first two NICs change.
> >
> > Of course adding a fourth and fifth NIC multiplies the identification
> > problem.  Yes, some of my routers are supporting five network segments.
> >
> > My question is, what's the algorithm for assigning Ethernet
> > designations?  I know it not placement order in the PCI bus, and I know
> > its not the NIC data-link address.
> >
> > So what is it?
>
> I know the order of the modules can change the eth ordering, but if you
> use the same module for all cards, it will be determined by how the
> kernel probes the pci bus.  I think that will be by I/O address, but I'm
> not positive.  This could be tested with cards that allow hard-setting
> of the I/O and some time swapping cards.
>
> HTH
>
> Derek

Another factor will be the characteristics of the driver;  for example the
3c503.o looks for default IO addresses,  in a certain order.
If you have a 3c503 set up with a non-default ( as defined by the driver )
IO port it might skip the lower IO port card for the first card with a
driver hard-coded port.