/sbin/iptables -> /sbin/iptables-legacy-multi /sbin/ip6tables -> /sbin/ip6tables-legacy-multi /sbin/iptables-save -> /sbin/ip6tables-legacy-multi /sbin/iptables-restore -> /sbin/ip6tables-legacy-multi
The iptables version string will indicate whether the legacy API (get/setsockopt) or the new nf_tables API is used:
iptables -V iptables v1.7 (legacy)
When inserting a rule using iptables -A or iptables -I, iptables first needs to retrieve the current active ruleset, change it to include the new rule, and then commit back the result. This means that if two instances of iptables are running concurrently, one of the updates might be lost. This can be worked around partially with the --wait option.
There is also no method to monitor changes to the ruleset, except periodically calling iptables-legacy-save and checking for any differences in output.