Это наверное старый рфц

Some operators also use /126, /127, /112 or an alternative prefix assignment instead of /64 for managed links where addresses on the link are manually configured, and according to RFC 6164, a /127 is suggested to prevent, among others, the Neighbor Discovery exhaustion attack (RFC 6583). Please note, that not all equipment currently supports this option, so /64 is still the safest approach and has the advantage of being future proof in the event that new standards make usage of the other 64 bits for other purposes or the link becomes point-to-multipoint, etc. Furthermore, some ISP hardware has limitations in using prefixes longer than /64, so the use of non-/64 prefixes will use more resources on these devices. If we decide to use /127 for each point to point link, then it is also advisable to allocate a /64 for each link and use just one /127 out of it.

какие-то странные решения выделять на п2п 64 перфикс, но занимать только /127