SendRelease isn't part of dhcp overrides

[Christian Scheuermann]

Every time a do a "netplan apply" my dhcp server assigns a new ip address to my device.

I've sniffed the network traffic and before a "dhcp discover" message there is a "dhcp release" message.

I've modified the .network files and add "SendRelease=false" to the DHCP-Section. Restart the networkd results in a new "dhcp discover" message, but the "dhcp release" message isn't send.

Is it possible to add send-release to the dhcp overrides?

[Lukas Märdian (slyon)]

This sounds like a useful addition. Do we know if there is a similar setting for the NetworkManager backend?

[Christian Scheuermann (christian-scheuermann)]

I can't find anything about in the source code at the moment.

But there is an issue regarding this topic:
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/742

[Roy Yang (royyang)]

This is a good feature to add into netplan.

In systemd v244, systemd-networkd has a default behavior change on the KeepConfiguration configuration. Before this change, VMs will not send the DHCP lease release message to the DHCP server on shutdown or reboot. After this change, VMs will send such messages and return the IPs to the DHCP server. As a result, the released IP may be reallocated to a different VM and/or a different IP may be assigned to the VM, resulting in IP conflicts.

Sometimes, we want to avoid sending DHCP release. For now, we have to change systemd configuration file. It will be nice for netplan to take key/value and add into .network config.