OSPFv3 - router ospfv3 command

When implementing OSPF so that OSPFv3 is used, it is necessary to implement the router ospfv3 [proccesID] command in order to enable the OSPF process, even if no additional commands are issued under that configuration mode.

Even though OSPFv3 configurations are applied to the interface rather than the OSFPv3 process, the router ospfv3 [proccesID] command must still be applied to activate the OSPFv3 process.

https://networklessons.com/ospf/ospfv3-for-ipv4-configuration/