We will define an authentication list that will reference the configured radius server group in Step 2. This authentication list will be referenced when we configure the IKEv2 Profile later in this guide.

ISR-LAB(config)#aaa authentication login authC-list group rad-group local

The above command defines an authentication list called rad-list. This list tells the router to use the radius group rad-group first to authenticate the user. If the radius servers are not available(dead), then local user database will be used for authentication. something like a failover if one method fails.