There are some notable differences in the configuration of EIGRPv4 and EIGRPv6 in Cisco IOS software. The first notable difference is the way in which the routing protocol is enabled. For EIGRPv4, the router eigrp [ASN] global configuration command is required to enable EIGRPv4 routing and to specify the EIGRPv4 autonomous system number (ASN). When configuring EIGRPv6, the ipv6 router eigrp [ASN] global configuration command is used instead to enable EIGRPv6 and to specify the local router ASN.
While enabling EIGRPv4 and EIGRPv6 is somewhat similar, there is a very notable and significant difference in the protocol states once the routing process has been enabled. By default, when EIGRPv4 is enabled, the protocol automatically starts and, assuming correct configuration, begins sending Hello packets on all specified operational interfaces. When enabling EIGRPv6 in Cisco IOS software, by default, after the protocol has been enabled, it remains in the shutdown state. This means that even if enabled under specified interfaces, the EIGRP process will not be operational until the no shutdown router configuration command is issued.
Yet another configuration difference between EIGRPv4 and EIGRPv6 is that with EIGRPv6, the router ID is mandatory and must be specified in IPv4 dotted-decimal notation. When assigning the RID, keep in mind that the address does not have to be a routable or reachable address.
NOTE: If there are any interfaces with IPv4 addresses configured on the local router, then the router will select the router ID from these interfaces – preferring Loopback interfaces, and then using physical interfaces if no Loopback interfaces are configured or operational on the router. The highest IP address of the Loopback interface(s), if up, will be selected. If not, the RID will be selected from the highest IP address of the physical interfaces, if up. If neither is configured on the router, the eigrp router-id [IPv4 Address] command must be used.