Comment 1 for bug 1721223

I spend a bit of time debugging this with xnox. Here some of the results:

# How to reproduce:
I setup a isc-dhcp-server with a fixed IP for my test rpi2 set to default/max lifetime of 120sec. The rpi2 was connected to the network with the isc-dhcp-server but unmodified otherwise. Once the pi2 connected and got an IP I switched the default IP to +1 and reloaded the isc-dhcp-server configuration. When the lease expired I could see the same as the OP - i.e. both IPs got removed.

# Related upstream bugs:
The patch from https://github.com/systemd/systemd/issues/5625 did not help with the issue

# Log
The full log of systemd-networkd is available here: http://paste.ubuntu.com/25686225/ - it was obtained by adding [Service]\nEnvironment=SYSTEMD_LOG_LEVEL=debug for the systemd-networkd.service.

The relevant lines:

Mar 14 21:02:52 localhost.localdomain systemd-networkd[7660]: eth0: Adding address: 192.168.1.124/24 (valid for 2min)
Mar 14 21:02:52 localhost.localdomain systemd-networkd[7660]: Sent message type=signal sender=n/a destination=n/a object=/org/freedesktop/network1/link/_33 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=16 reply_cookie=0 error=n/a
Mar 14 21:02:52 localhost.localdomain systemd-networkd[7660]: Sent message type=signal sender=n/a destination=n/a object=/org/freedesktop/network1 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=17 reply_cookie=0 error=n/a
Mar 14 21:02:52 localhost.localdomain systemd-timesyncd[995]: Network configuration changed, trying to establish connection.
Mar 14 21:02:52 localhost.localdomain systemd[1]: Starting Update resolvconf for networkd DNS...
Mar 14 21:02:56 localhost.localdomain systemd-networkd[7660]: NDISC: Sent Router Solicitation
Mar 14 21:03:00 localhost.localdomain systemd-networkd[7660]: NDISC: Sent Router Solicitation
Mar 14 21:03:04 localhost.localdomain systemd-networkd[7660]: NDISC: Invoking callback for 't'.
Mar 14 21:03:22 localhost.localdomain systemd[1]: Started Update resolvconf for networkd DNS.
Mar 14 21:03:51 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x22f0fd4b): REQUEST (renewing)
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x22f0fd4b): REQUEST (rebinding)
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x22f0fd4b): NAK: requested address is incorrect
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): REBOOT in 0
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): DISCOVER
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): OFFER
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): REQUEST (requesting)
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): ACK
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): lease expires in 1min 57s
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): T2 expires in 1min 43s
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: DHCP CLIENT (0x4d15b90b): T1 expires in 1min
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: eth0: DHCPv4 address 192.168.1.125/24
Mar 14 21:04:36 localhost.localdomain systemd-timesyncd[995]: Network configuration changed, trying to establish connection.
Mar 14 21:04:36 localhost.localdomain systemd-networkd[7660]: eth0: Updating address: 192.168.1.125/24 (valid for 2min)
Mar 14 21:04:36 localhost.localdomain systemd[1]: Starting Update resolvconf for networkd DNS...
Mar 14 21:04:52 localhost.localdomain systemd-networkd[7660]: eth0: Removing address: 192.168.1.125/24 (valid for 1min 44s)
Mar 14 21:04:52 localhost.localdomain systemd-networkd[7660]: eth0: Removing address: 192.168.1.124/24 (valid for 0)
Mar 14 21:04:52 localhost.localdomain systemd-networkd[7660]: Sent message type=signal sender=n/a destination=n/a object=/org/freedesktop/network1/link/_33 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=18 reply_cookie=0 error=n/a
Mar 14 21:04:52 localhost.localdomain systemd-networkd[7660]: Sent message type=signal sender=n/a destination=n/a object=/org/freedesktop/network1 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=19 reply_cookie=0 error=n/a
Mar 14 21:04:52 localhost.localdomain systemd-timesyncd[995]: Network configuration changed, trying to establish connection.
Mar 14 21:05:06 localhost.localdomain systemd[1]: Started Update resolvconf for networkd DNS.