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Date: Wed, 7 Jul 2010 17:39:37 -0500
From: Brian Kroth <bpkroth@gmail.com>
To: Michael Di Domenico <mdidomenico4@gmail.com>
Cc: linux-net@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: nic enumeration
Message-ID: <20100707223935.GD23117@gmail.com>
Reply-To: Brian Kroth <bpkroth@gmail.com>
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Michael Di Domenico <mdidomenico4@gmail.com> 2010-07-07 18:25:
> I have an issue where I have an onboard NIC with effectively three
> ports, no other NIC ports/chips are in the system
>=20
> Nic0: xx:xx:xx:00:00:02
> Nic1: xx:xx:xx:00:00:01
> IPMI: xx:xx:xx:00:00:03
>=20
> When I boot RedHat Linux, Nic1 becomes Eth0 and Nic0 becomes Eth1.
>=20
> I understand there is a disconnect between BIOS and linux on which
> device should get which Eth, as well as, what ensues when you have PCI
> cards along side onboard ports.
>=20
> What I'm curious about is how/why Linux actually decides Nic1 should be E=
th0?
>=20
> My theory is it starts on the lowest MAC address and works up,
> depending partly on driver load order.
>=20
> Given the above scenario, swapping the MAC addresses between Nic1 and
> Nic0 would clear this issue.
>=20
> Can anyone confirm or deny this?  Or explain/point me to, how it actually=
 works.

Look into udev.  It should maintain some rules that dictate that
mapping.  If not you can potentially write/alter some to make it do what
you want/expect.

On my systems the place to look is generally here:
/etc/udev/rules.d (user rules)
/lib/udev/rules.d (system rules)

There may be others.

Cheers,
Brian

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