linux-kernel - Re: nic enumeration

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Message-ID: <20100708012120.GB11419@auslistsprd01.us.dell.com>
Date:	Wed, 7 Jul 2010 20:21:20 -0500
From:	Matt Domsch <Matt_Domsch@...l.com>
To:	Michael Di Domenico <mdidomenico4@...il.com>
Cc:	linux-net@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: nic enumeration

On Wed, Jul 07, 2010 at 06:25:53PM -0400, Michael Di Domenico wrote:
> I have an issue where I have an onboard NIC with effectively three
> ports, no other NIC ports/chips are in the system
> 
> Nic0: xx:xx:xx:00:00:02
> Nic1: xx:xx:xx:00:00:01
> IPMI: xx:xx:xx:00:00:03
> 
> When I boot RedHat Linux, Nic1 becomes Eth0 and Nic0 becomes Eth1.
> 
> 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.
> 
> What I'm curious about is how/why Linux actually decides Nic1 should be Eth0?
> 
> My theory is it starts on the lowest MAC address and works up,
> depending partly on driver load order.
> 
> Given the above scenario, swapping the MAC addresses between Nic1 and
> Nic0 would clear this issue.
> 
> Can anyone confirm or deny this?  Or explain/point me to, how it actually works.

http://lwn.net/Articles/356900/

And on a system where you can use udev rules, the
70-persistent-net.rules file can be used to make them constant, by
using the MAC address to force the names to be what you want.

-- 
Matt Domsch
Technology Strategist
Dell | Office of the CTO
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