It may be beneficial in some deployments for operators to migrate from 64-bit to 128-bit WAN mode. For example, the ability to assign consecutive 128-bit address and minimize the subnet required for Residential Gateway or Cable Modem IPv6 DHCP IANA WAN management address.
A 64-bit WAN mode subscriber interface cannot be changed into a 128-bit WAN mode subscriber interface in real time. To migrate to a 128-bit WAN mode subscriber interface, the 64-bit WAN mode subscriber interface must be a removed and re-created. The 64-bit configuration must be copied, shut down, and the configuration removed. The configuration can be pasted back with the 128-bit mode added to the subscriber interface. Below are some migration scenarios.