My home internet connection comes with proper dual-stack support. I get a public IPv4 address via DHCP, a /128 (IA_NA) and a /48 IPv6 prefix (IA_PD) via DHCPv6.

Traditionally you would configure your networking via iproute2 and then fork-off a DHCP client to configure the external addresses.

Usually all of that is being hidden from you through wrappers (like Debian’s ifupdown). The configuration would be set, the daemons fired off and hopefully everything would go well.

The limitations of the system become visible once you have a more dynamic set of interfaces that have to be initialized in some order, some VPN device that depend on the uplink connection etc. While systems like ifupdown have employed hooks of all sorts that you still end up writing a bunch of (inlined) shell scripts that deal with some little details of your setup. Adding sleep statements at worst. Things get tricky when one interface going up changes things on another interface or even system wide (think sysctl, iptables, starting a VPN daemon, …).