Final answer:
Forgetting to create a routing process with the ipv6 router rip name command before enabling RIPng on an interface results in that interface not participating in RIPng routing, thus not advertising or learning about routes.
Step-by-step explanation:
If you forget to create a routing process using the ipv6 router rip name command before enabling RIPng on an interface, the router will not start RIP routing for IPv6.
RIPng needs to be explicitly enabled for each IPv6 network or interface on which it will operate, and a routing process needs to be named and configured beforehand using the ipv6 router rip name command. Without creating a routing process, the enabled interface will not participate in RIPng routing and will not advertise its presence or learn about other RIPng-enabled routes from neighbors.