IPv6 Basics

Loopback: ::1/128
Multicast: FF00::/8
Link Local: FE80::/10 - used for stateless auto-configuration, Neighbor discovery, Router discovery
FC00::/7 Unique Local, Unicast (equivalent to the IPv4 private addresses), not routable via global BGP
EUI-64 - always use the /64 addresses for all the INTERFACES
!!!(MAC can be converted into EUI-64 format to get the interface address)

ARP has been replaced with ICMPv6 Neighbor Discovery.
Inverse ARP has been removed, so for NBMA networks we need to provide a static L2-L3 mapping

TIP: before enabling IPv6 on a router and configuring the interfaces male sure there is a IPv4 connectivity

IPv6 is not enabled by default, so first enable IPv6 globally on the Router/Switch:
(config)#ipv6 unicast-routing

On a ROUTER you should enable IPv6 on an interface:
(config-if)#ipv6 enable
!!!LINK-LOCAL address is generated based on the interfaces MAC Address by doing "ipv6 enable"

Assign the UNICAST IPv6 address:
(config)#no switchport <--- DONT FORGET on 3560 OR 3750
(config-if)#ipv6 add 12:1:1::3/64

Assign a LINK-LOCAL IPv6 Address, if you want to configure it STATICALLY:
(config-if)#ipv6 address FE80::1 link-local
!!!Be sure it starts with FE80, or you will get a message "% Invalid link-local address"

By default IPv6 has Neighbor Discovery as a L2-L3 mapping mechanism, instead of ARP. To debug it do:
#debug ipv6 nd

When you configure the "ipv6 enable" on the interface, the Link Local address is assigned:
*Nov 21 08:21:02.068: ICMPv6-ND: Sending NS for FE80::21E:BEFF:FE5D:27F0 on FastEthernet0/0
!!!NS -Neighbor Solicitation
*Nov 21 08:21:03.068: ICMPv6-ND: DAD: FE80::21E:BEFF:FE5D:27F0 is unique.
!!!FE80::21E:BEFF:FE5D:27F0 Assigned. DAD - Duplicate Address Detection confirms IP is UNIQUE!
*Nov 21 08:21:03.068: ICMPv6-ND: Sending NA for FE80::21E:BEFF:FE5D:27F0 on FastEthernet0/0
!!!NA - Neighbor Advertisment for routers Link Local address
*Nov 21 08:21:03.068: ICMPv6-ND: Address FE80::21E:BEFF:FE5D:27F0/10 is up on FastEthernet0/0
!!!Interface comes UP because noone complained

Check if the interface got the correct IPv6 Address:
#sh ipv6 int br
FastEthernet0/0            [up/up]
    FE80::21E:BEFF:FE5D:27F0
FastEthernet0/1            [administratively down/down]
Serial0/1/0                [up/down]
Serial0/1/1                [administratively down/down]
Serial0/2/0                [administratively down/down]

When you SHUT the local interface, the Link Local address is deleted:
*Nov 21 08:19:12.972: ICMPv6-ND: Sending Final RA on FastEthernet0/0
*Nov 21 08:19:12.984: ICMPv6-ND: STALE -> DELETE: FE80::213:60FF:FE85:AEEA

And we are finally reaching my favorite change in the IPv6, the NEIGHBOR DISCOVERY and DISPLAY:
#show ipv6 neighbors
IPv6 Address                              Age Link-layer Addr State Interface
12:1:1:12::1                                0 0013.6085.aeea  STALE Fa0/0 <- UNICAST
FE80::1                                     0 0013.6085.aeea  STALE Fa0/0 <- LINK-LOCAL