EIGRPv6

The difference with OSPF is that even if you configure it on the interface:
(config-if)#ipv6 eigrp 100
it will not form an adjacency unless you DEFINE THE ROUTER-ID, and do a NO SHUT:
(config-rtr)#eigrp router-id 1.1.1.1
(config-rtr)#no shut <-ON SOME IOS VERSIONS NOT NEEDED, BUT DO IT JUST IN CASE...
*Dec  1 11:18:08.343: %DUAL-5-NBRCHANGE: EIGRP-IPv6 100: Neighbor FE80::4 (Serial1/0.14) is up: new adjacency

!!!BE SURE TO DEFINE THE METRIC WHEN REDISTRIBUTING INTO EIGRP, or it will not work!!!
(config-rtr)#no redistribute ospf 1  metric 1 1 1 1 1

To change the timers on the interface the command is a bit BACKWARDS, as in - "" ipv6 hello-interval eigrp..":
(config-if)#ipv6 hello-time eigrp 100 10 <-HELLO
(config-if)#ipv6 hold-time eigrp 100 40 <-DEAD

The command for checking the current timers is also unintuitive, cause you need to add "details" to the end:
#sh ipv6 eigrp interfaces detail  | i Hello
  Hello-interval is 10, Hold-time is 40
  Hello-interval is 60, Hold-time is 180

!!!BE CAREFULL WITH FRAME RELAY, cause EIGRP has SPLIT HORIZON enabled by default on multipoint interfaces, so make sure if you need to disable it or not:
(config-subif)#no ipv6 split-horizon eigrp 100

Like in EIGRPv4, on EIGRPv6 EIGRP Patckets use UP TO 50% of the Links BW. To change that (to 25% in this example):
(config-subif)#ipv6 bandwidth-percent eigrp 100 25

Another similarity to EIGRPv4, you can use "summary-address" to inject the default route:
(config-if)#ipv6 summary-address eigrp 100 ::0/0
*Dec  1 12:32:28.571: %DUAL-5-NBRCHANGE: EIGRP-IPv6 100: Neighbor FE80::2 (Ethernet0/0) is resync: summary configured
*Dec  1 12:32:28.571: %DUAL-5-NBRCHANGE: EIGRP-IPv6 100: Neighbor FE80::3 (Ethernet0/0) is resync: summary configured

EIGRPv6 Authentication: Also similar to EIGRPv4

Step 1: Define the Key Chain
(config)#key chain MAT
(config-keychain)#key 1
(config-keychain-key)#key-string Cisqueros

Step 2: Apply the key chain to the interface:
(config-if)#ipv6 authentication key-chain eigrp 100 MAT

Step 3: Turn ON the authentication on the interface, in this example MD5:
(config-if)#ipv6 authentication mode eigrp 100 md5

Some ADDITIONAL features:
Make sure the incoming prefixes are in less then 50 hops (TTL <= 50)
(config-rtr)#metric maximum-hops 50

"Tune" the Active Time (time before declaring a router STUCK IN ACTIVE - SIA)
(config-rtr)#timers active-time ?
  <1-65535>  active state time limit in minutes
  disabled   disable time limit for active state