This remember me a old FIXED bug but with forcedeth Bug 75871[#1] that I reported.

There is some kind of race condition with new systemd-networkd (219-5) because network interface (driver r8169), randomly does no get initialized on boot (no ip addr, no link up).
This at least happens with linux-4.0-2, no issue under 3.14.39-1. No issue with systemd-218-2 at all (3.14/4.0). This is on Arch Linux with stock kernel.

While trying to debug the issue, I discovered a workaround, if I enable log-level debug in networkd, interface always gets initialized on boot. (The same workaround used in 75871)


# cat /etc/systemd/system/systemd-networkd.service.d/debug.conf
[Service]
Environment=SYSTEMD_LOG_LEVEL=debug

# cat /etc/systemd/network/20-net0.link
[Match]
MACAddress=00:18:f3:02:08:03

[Link]
Name=net0

# cat /etc/systemd/network/20-net0.network
[Match]
Name=net0

[Network]
Description=red
Address=192.168.90.66/24
Gateway=192.168.90.1