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Find Ethernet Card by slot Linux


I was somewhat frustrated when network interface enumeration suddenly changed (around 6.3) in a seemingly random manner.  I noticed the madness now had a pattern... and regardless of my attempts to manually manage my interfaces using UDEV (as I had in the past) it would just screw everything up.
So - I conceded and allowed the system to manage itself how it wanted and I discovered that was the best option.

In the past, you may end up with eth0 being on a PCI card, while the onboard would be eth3.  Since the release of the new standard, the onboard are identified as em (for "embedded" I believe) and the other network interfaces are identified by slot number and interface (i.e. p2p1 - slot 2, eth 1).

A person who posts on the Red Hat Customer Portal had an amazing find and submitted the following:

....Dell (who wrote biosdevname and released it under GPL) have two white papers on the subject at the project page: http://linux.dell.com/biosdevname/
From the Consistent Network Device Naming in Linux paper:
  • Firmware information that "biosdevname" utilizes to suggest new names
    The system BIOS indicates the order of Onboard Network Devices to the OS via SMBIOS type 41 records.
    The system BIOS provides "system slot information" to the OS via type 9 records.
    The biosdevname makes use of SMBIOS type 41 to suggest names to the onboard network devices and type 9 records to suggest new names for PCI add-in adapters.
    The biosdevname falls back on PCI IRQ Routing Table in the absence of the above mentioned information.
You should be able to see this SMBIOS information with dmidecode -t 41 and dmidecode -t 9 ...
-- Jamie Bainbridge

I'll miss the foo of using lspci and /etc/udev/rules.d/70-persistent-network.rules :-(  Not really!

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