EIRGP router id is mandatory with IPV6 EIGRP. Is <IPV6 Router EIGRP X >mandatory if you have at least one IPV4 interface configured that can serve as a router EIGRP router id? Could you then get away enabling EIGRPV6 without using the ipv6 router command?
You will need to type in "ipv6 router eigrp x" even if you have a valid ipv4 address configured that can be used as a router-id (rid). Best practice would be to configure the rid explicitly and not to let the router select it automatically.
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