[Bug 1776013] Re: systemd-networkd: DHCP lease lost (Ubuntu 18.04)

[Dmitriy Altuhov]

To fix it with cloud-init we need to create an override-file for netplan
like this:

/etc/netplan/99-critical-dhcp.yaml
network:
    version: 2
    ethernets:
        ens2:
            dhcp4: true
            critical: true

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Title:
  systemd-networkd: DHCP lease lost (Ubuntu 18.04)

Status in systemd package in Ubuntu:
  Invalid

Bug description:
  I have a Linux router whose external Ethernet interface is configured from ISP's DHCP server.
  After its migration from Ubuntu 16.04 + ifupdown + isc-dhcp-client to Ubuntu 18.04 + netplan.io + systemd-networkd, I noticed that systemd-networkd plays overly fairly when it can not get a timely renew response from ISP's DHCP server: it honestly removes the dynamic IP from the interface and restores (often the same) IP only when ISP's DHCP server gives it a proper response again. Which causes 1..5-minute pauses in Internet availability since my ISP's DHCP server is for some reason flaky, i.e. it can become unresponsive for some periods of time. I never noticed this problem with isc-dhcp-client, and started noticing it only after migrating DHCP client role to systemd-networkd.
  The question is, can I (or you) make systemd-networkd DHCP client behave more relaxedly ?
  I know that most DHCP clients (isc-, pump, dhcpcd) at some stage of their development decided to implement such relaxed logic, i.e. to keep last-configured dynamic IP on the interface despite the lack of responses from DHCP server. As this is easier to implement than to make ISP staff fix their services, I would suppose there should be some knob in systemd-networkd settings. Or, at least, an idea to implement something similar in the future.

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