If you want the router to advertise an IPv6 address prefix on the designated interface, enter a 64-bit address prefix. You will be prompted for additional address prefixes until you press [Enter] in response to this prompt.      

If you are a 6to4 Border Router, you must advertise the 64-bit 6to4 prefix on the link that is connected to your 6to4 site.      

If you do not want the router to advertise an IPv6 address prefix on the designated interface, enter Done. If you enter no address prefixes, this feature is disabled.