linux-kernel - Re: nic enumeration

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Date:	Wed, 7 Jul 2010 17:39:37 -0500
From:	Brian Kroth <bpkroth@...il.com>
To:	Michael Di Domenico <mdidomenico4@...il.com>
Cc:	linux-net@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: nic enumeration

Michael Di Domenico <mdidomenico4@...il.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
> 
> 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.

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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