A good example of a service that needs to be started before networking is the firewall service. You can take a look at what your distro of choice is providing for hints. But essentially it boils down to something like this:
Fedora's iptables.service: Before=network-pre.target Wants=network-pre.target Ubuntu's ufw.service (bit more elaborate, no idea why): DefaultDependencies=no Before=network-pre.target Wants=network-pre.target local-fs.target After=local-fs.target
