SM
Ну, оказалось это не рфс, а, например, ripe-655, раздел 5.3
https://www.ripe.net/publications/docs/ripe-690#4-2-3--prefixes--longer-than--56
Assigning a /64 or longer prefix does not conform to IPv6 standards and will break functionality in customer LANs. With a single /64, the end customer CPE will have just one possible network on the LAN side and it will not be possible to subnet, assign VLANs, alternative SSIDs, or have several chained routers in the same customer network, etc.
