[clug] dd

Andrew Janke a.janke at gmail.com
Sun Apr 11 22:35:10 MDT 2010

> Around 2003-2004 I definitely had a box which would flip the order of
> detection of the NICs on boot with the same kernel.  I could demonstrate
> this behaviour.  ie, if I booted it 5 or 6 times I would see the problem
> occur at least once.  Unfortunately I was using it as a firewall when I
> discovered this problem - the damn thing flipped the interfaces and suddenly
> the firewall was facing the wrong way.


> I've met other sysadmins who have also reported this problem under Linux.
> The problems seem to have melted away when iftab came in to common use - but
> this would work around the problem rather than fix it.  Now we have udev of
> course.

Which just means you have to do things in a more complex fashion. :)

My solution to this is to always install dual NICS from identical
manufacturers (and disable the internal one in BIOS if you couldn't
match it). Usually this means a Intel Pro 1000 dual port card.

Problem solved as then they always seem to come up predictably. I have
also found this to change from kernel to kernel based upon some
inbuilt module load order that I don't seem to be able to control.

I once ran a lab with 100+ heterogeneous debian machines with dual
network cards, one for 100MB official traffic, the second GB for local
NFS cluster traffic as we were overloading the hosting unis switches.

It was a recipie for disaster as they rebooted/upgraded individually,
some numbered the PCI slots from bottom up, some from top down, etc.
In the end I got sick of it, pulled every single NIC, put them all in
a big pile and then sorted out identical ones for each machine... :)

Andrew Janke
(a.janke at gmail.com || http://a.janke.googlepages.com/)
Canberra->Australia    +61 (402) 700 883

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