[apologies to package aliases getting this twice due to autocomplete fail]
I've been trying to make sense of the NEWS item in isc-dhcp-client (that alternatives are needed) in combination with the functionality of ifupdown and what the implications are for debian upgrades generally.
isc-dhcp-client as of the last upgrade is telling users to stop using it (the default dhcp client for debian).
ifupdown (the traditional tool for managing networking on debian systems) has a Recommends on "isc-dhcp-client | dhcp-client". "dhcp-client" is a virtual package provided by "dhcpcanon" (version 0.8.5, which hasn't been touched in 4 years), "isc-dhcp-client", and "dhcpcd5" (which will trash a working configuration managed by ifupdown if installed, as it will try to take over interfaces currently set, e.g., to manual). This seems suboptimal at best.
I believe that ifupdown will attempt to use udhcpd if installed, which should be a mostly-transparent change (except for the potential loss of lease information and any customization of dhclient scripts) but it isn't even on the ifupdown recommends list.
ifupdown also (used to?) use pump, but that package went away a long time ago.
So what's the path forward, maintaining compatibility and not breaking systems upgrading from current stable? Do we come up with a dhcpcd5 variant that *only* touches interfaces it is directed to touch via /etc/network/interfaces? Do we add udhcpcd to the "dhcp-client" virtual package and/or make it the default for ifupdown? Do we fork isc's dhcp suite and just continue to use dhclient? Revive pump? Something else?