> The Linux box I use as a router gets a single (i.e., /128) address from Spectrum Cable on its upstream interface, and it has to explicitly ask for a separate

> The Linux box I use as a router gets a single (i.e., /128) address from Spectrum Cable on its upstream interface, and it has to explicitly ask for a separate /64 prefix to advertise on the local interface Ask for a /56! Spectrum in Los Angeles hands out /56s, and I understand many other residential IPv6 ISPs do as well. You get your own 8 bits worth of subnets on top of /64 for easy SLAAC address assignment. This works "for free" not only because the IPv6 address space is large enough to do this, but more importantly because IPv6 does NOT have any fixed subnet sizes - routing is hierarchical and subnet assignment is transparent. /64 is just the size used by SLAAC address auto-configuration, another bit of IPv6 magic.