If you don't mind, gents, I took the liberty of digging a bit into these guts.
I reproduced this on a clean Ubuntu 26.04 (Resolute) environment running netplan.io 1.2 and systemd 259.5-0ubuntu3.4. The actual issue is this: 1. How systemd 259 handles [DHCP]: In systemd-networkd, the legacy `[DHCP]` section is not completely ignored. It is mapped via a compatibility alias in `src/network/networkd-network-gperf.gperf`: - Line 255: `DHCPv4.ClientIdentifier` -> `Network.dhcp_client_identifier` - Line 641: `DHCP.ClientIdentifier` -> `Network.dhcp_client_identifier` When Netplan writes `[DHCP]` with `ClientIdentifier=mac`, systemd- networkd parses it into `Network.dhcp_client_identifier = DHCP_CLIENT_ID_MAC`. Checking `networkctl status <iface>` confirms that `DHCPv4 Client ID:` is set to the MAC address when no conflicting configuration exists. 2. Why this causes confusion and real breakage: - `man systemd.network(5)` dropped `[DHCP]` years ago; only `[DHCPv4]` and `[DHCPv6]` are documented. Seeing `[DHCP]` in `networkctl cat` leads users to believe it is unparsed. - Global config `/etc/systemd/networkd.conf` only recognizes `[DHCPv4]`, not `[DHCP]`. - If any drop-in in `/etc/systemd/network/` or `/etc/systemd/networkd.conf.d/` configures `[DHCPv4]`, systemd's section parser prioritizes `[DHCPv4]` settings over the legacy `[DHCP]` alias, which silently overrides or masks Netplan's generated values. - In `netplan/src/networkd.c`, Netplan still carried legacy logic from 2017 emitting `[DHCP]` for both DHCPv4 and DHCPv6. 3. Resolution: Netplan should stop emitting the legacy `[DHCP]` block and output canonical `[DHCPv4]` and `[DHCPv6]` sections matching modern systemd-networkd standards. Upstream pull request submitted for review: https://github.com/canonical/netplan/pull/617 I also attached the patch file for review. ** Patch added: "Emit [DHCPv4] and [DHCPv6] in networkd backend instead of legacy [DHCP]" https://bugs.launchpad.net/ubuntu/+source/netplan.io/+bug/2167907/+attachment/6002833/+files/lp2167907_networkd_dhcp4_section.patch ** Changed in: netplan Status: New => Confirmed ** Changed in: netplan.io (Ubuntu) Status: New => Confirmed -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2167907 Title: 'dhcp-identifier: mac' in netplan .yml config is ignored by systemd To manage notifications about this bug go to: https://bugs.launchpad.net/netplan/+bug/2167907/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
