[ale] eth numbering change

Alex Carver agcarver+ale at acarver.net
Wed Feb 8 16:31:29 EST 2017


Others have mentioned persistent information on the system (udev rules,
previously seen NICs) but there's also just the basic order of bus
enumeration.  Slot 2 might actually be scanned before Slot 1 (bus order
is determined by the physical wiring on the board and how they are wired
to the bus controller).  If Slot 2 comes up first then the kernel sees
whatever is there first and assigns eth0 as the first available device.
Then it scans Slot 1 and assigns the next available eth1.

On 2017-02-08 11:05, Brian Stanaland wrote:
> Hello,
> 
> This one has bugged me for a while.
> 
> I understand that the numbering of network interfaces can change when adding a 
> network card. What I can't figure out is why it's inconsistent. I have two 
> identical servers, same mobo, same NICs in slot 1, same firmware, etc. I add a 
> NIC in slot 2 on both severs and reboot. Why does one show the new NIC as eth0 
> and the other shows the new NIC as eth1?
> 
> Google only turns up how to set persistence.
> 
> --Brian
> 
> 
> -- 
> "Anyone who has never made a mistake has never tried anything new." -Albert Einstein
> 
> 
> 
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