Cisco related stuff and IPv6

 ipv6 unicast-routing
 ipv6 cef

 interface FastEthernet0/0
    ipv6 enable
    ipv6 address xx:xx:xx:xx:xx::x/yy

 (config)#sdm prefer dual-ipv4-and-ipv6 default
 # sh sdm prefer

 The current template is "desktop default" template.
 The selected template optimizes the resources in
 the switch to support this level of features for
 8 routed interfaces and 1024 VLANs. 

  number of unicast mac addresses:                  6K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    8K
    number of directly-connected IPv4 hosts:        6K
    number of indirect IPv4 routes:                 2K
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      512
  number of IPv4/MAC security aces:                 1K
 
 On next reload, template will be "desktop IPv4 and IPv6 default" template.

reload is needed