An issue has cropped up recently on my Raspberry Pi Model B+ (armv6): when the internet connection is lost (due to my ISP router crashing and resetting itself), systemd-networkd fails to reconnect to the network automatically. Instead, I have to physically unplug/replug the ethernet cable to restore the connection. Here is the journalctl output from immediately before/after this happens:
$this->bbcode_second_pass_code('', 'Feb 10 09:56:11 mpdpi kernel: smsc95xx 1-1.1:1.0 eth0: Link is Down
Feb 10 09:56:11 mpdpi systemd-networkd[193]: eth0: Lost carrier
Feb 10 09:56:11 mpdpi systemd-networkd[193]: eth0: DHCP lease lost
Feb 10 09:56:11 mpdpi systemd-networkd[193]: eth0: DHCPv6 lease lost
Feb 10 09:56:11 mpdpi systemd-timesyncd[212]: No network connectivity, watching for changes.
Feb 10 10:08:07 mpdpi kernel: smsc95xx 1-1.1:1.0 eth0: Link is Up - 100Mbps/Full - flow control off
Feb 10 10:08:07 mpdpi systemd-networkd[193]: eth0: Gained carrier
Feb 10 10:08:07 mpdpi systemd-timesyncd[212]: Network configuration changed, trying to establish connection.
Feb 10 10:08:07 mpdpi systemd-networkd[193]: eth0: DHCPv4 address 192.168.1.71/24 via 192.168.1.254')
For reference, here is the network configuration in /etc/systemd/network/eth0.network (which I believe is just the distribution default config; I have no memory of ever editing it):
$this->bbcode_second_pass_code('', '[Match]
Name=eth0
[Network]
DHCP=yes
DNSSEC=no')
I can't pinpoint exactly when this problem started (i.e. can't tie it to a particular systemd or kernel upgrade), but it is a recent development, on or about the time of the switchover to the 5.10.x kernel. I suspect this is a general software issue rather than a hardward/platform-specific issue; apologies if this would be better posted in the armv6 category.
Grateful for any suggestions anyone might have on how to fix this!