Comment 6 for bug 1777094

https://netplan.io/faq#example-for-an-ifupdown-legacy-hook-for-post-uppost-down-states

You can use a networkd-dispatcherd to hook on vlan0 becoming routeable
and then start/restart the dnsmasq service;

On Fri, Jun 15, 2018 at 12:36 PM, Hadmut Danisch <email address hidden> wrote:
> So it is not possible to have an interface as optional (for other
> reasons beyond that example) and still have a dnsmasq running for it?
>
> In former versions of ubuntu I had my bridges (some containing usb
> ethernet interfaces to bridge virtual with physical machines) configured
> in /etc/network/if-up.d, and started separate dnsmasq instances for
> every single one of these bridges.
>
> Now there is no regular way to start a daemon like dnsmasq through ifup-
> scripts, since netplan does not support them. Some people try to
> workaround that problem with udev clauses, starting systemd services,
> but then it's overcomplicated and error prone.
>
> So what is the offical way to have services like dnsmasq run for
> optional interfaces under 18.04?
>
>
> "Don't use optional" is a workaround, not a solution to the problem. If there is no ifup-script anymore, then how are services to be started, once the interface is up (late or just sometimes)?
>
> --
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> report.
> https://bugs.launchpad.net/bugs/1777094
>
> Title:
> dnsmasq started too early, not getting all interfaces
>
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