Hello
Here is a full discussion to understand how to:
https://learningnetwork.cisco.com/thread/29824
Here is the step-by-step configuration:
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-dhcp.html
SUMMARY STEPS
1. enable
2. configure terminal
3. ipv6 dhcp pool poolname
4. domain-name domain
5. dns-server ipv6-address
6. prefix-delegation ipv6-prefix/prefix-length client-duid [iaid iaid] [lifetime]
7. prefix-delegation pool poolname [lifetime valid-lifetime preferred-lifetime]
8. exit
9. interface type number
10. ipv6 dhcp server poolname [rapid-commit] [preference value] [allow-hint]
HTH,
Calin
