missing dhcp override for RouteTable

[Ross Vandegrift]

Hello,

I'm trying to add out-of-band network management to a system that uses netplan. I'd like the management routes to live in a non-default routing table so they cannot interfere with production interfaces. systemd-networkd's DHCP section supports RouteTable= for this use-case. But there's no corresponding dhcp override option in netplan.

As a workaround, I can add a systemd drop-in at e.g. /etc/systemd/network/10-netplan-mgmt.network.d/override.conf. This is suggested in a few similar bugs, but that approach has drawbacks:

- it splits the network config into two places, and requires the user to remember when networkd needs a reload before `netplan apply` works as expected.

- the systemd drop-in dir and the files that netplan generates must have matching names. Does netplan consider the file names it generates to be a stable interface?

- similarly, the user must remember that the configuration IDs now provide linkage between netplan's part of the network config and the rest.

- `netplan get` and `netplan status` no longer provide all of the important details, and the user must remember when and how they are incomplete. (or just avoid using them entirely)

- network drop-ins aren't so well-documented or well-supported by systemd (`systemctl edit` and `systemctl cat` don't seem to work on network units, for instance)

[Lukas Märdian (slyon)]

So do I understand correctly that you'd need an additional dhcp4/6-overrides setting in Netplan, specifiying the routing table that routes received from DHCP should be installed in?

I think that's a reasonable feature request. Pull requests welcome!

Could you please share the override.conf that you used as a workaround and links to the reference bugs mentioned above? Thanks!

[Ross Vandegrift (ross-kallisti)]

Yes, exactly right. I'd expect to be able to write something like:

  network:
    version: 2
    renderer: networkd
    ethernets:
      mgmt:
        dhcp4: true
        dhcp4-overrides:
          route-table: 23

For an example override, I had to create /etc/systemd/network/10-netplan-mgmt.network.d/override.conf with:

  [DHCP]
  RouteTable=
  RouteTable=23

Similar issues where missing features can be addressed with with drop-in workarounds:
 - https://bugs.launchpad.net/netplan/+bug/2023727
   - your comment #4 inspired my thoughts about the disadvantages of this scheme
 - https://bugs.launchpad.net/netplan/+bug/1771886