For yet unknown reasons some recently installed HPE DL360G10 running buster changed back the interface names from the expected "onboard" based names eno5 and eno6 to ethX after a reboot.

My current workaround is a link file which kind of enforces the onboard scheme.

$ cat /etc/systemd/network/101-onboard-rd.link 
[Link]
NamePolicy=onboard kernel database slot path
MACAddressPolicy=none

The hosts are running the latest buster kernel

Linux foobar 4.19.0-5-amd64 #1 SMP Debian 4.19.37-5+deb10u2 (2019-08-08) x86_64 GNU/Linu

A downgrade of the kernel did not change anything. So I currently like to believe this is not related a kernel change.

I tried to collect a few information on one of the broken systems while in a broken state:

root@foobar:~# SYSTEMD_LOG_LEVEL=debug udevadm test-builtin net_setup_link /sys/class/net/eth0
=== trie on-disk ===
tool version:          241
file size:         9492053 bytes
header size             80 bytes
strings            2069269 bytes
nodes              7422704 bytes
Load module index
Found container virtualization none.
timestamp of '/etc/systemd/network' changed
Skipping overridden file '/usr/lib/systemd/network/99-default.link'.
Parsed configuration file /etc/systemd/network/99-default.link
Created link configuration context.
ID_NET_DRIVER=i40e
eth0: No matching link configuration found.
Builtin command 'net_setup_link' fails: No such file or directory
Unload module index
Unloaded link configuration context.

root@foobar:~# udevadm test-builtin net_id /sys/class/net/eth0 2>/dev/null
ID_NET_NAMING_SCHEME=v240
ID_NET_NAME_MAC=enx48df37944ab0
ID_OUI_FROM_DATABASE=Hewlett Packard Enterprise
ID_NET_NAME_ONBOARD=eno5
ID_NET_NAME_PATH=enp93s0f0

Most interesting hint right now seems to be that /sys/class/net/eth0/name_assign_type is invalid While on sytems before the reboot that breaks it, and after setting the .link file fix, contains a 4.

Since those hosts were intially installed with buster there are no remains on any ethX related configuration present. If someone has an idea what is going on write a mail (sven at stormbind dot net), or blog on planet.d.o.

I found a vaguely similar bug report for a Dell PE server in #929622, though that was a change from 4.9 (stretch) to the 4.19 stretch-bpo kernel and the device names were not changed back to the ethX scheme, and Ben found a reason for it inside the kernel. Also the hardware is different using bnxt_en, while I've tg3 and i40e in use.