On 13/01/13 20:05, Tony Langdon wrote:
A /64 should do most home networks.
Where “most” doesn’t include power users. A /64 cannot be divided any further without breaking router advertisement (which you REALLY do not want to do). In fact, using anything other than a /64 on a direct interface (i.e. not a route) is officially deprecated. In addition, operating systems such as iOS or Android do not allow static configuration of IPv6 and thus completely depend on router advertisement. A fair few non-power users use multiple subnets without realising it — all the time I come across people who have purchased a wired-only ADSL modem, and put a wireless router behind it. That’s two (currently IPv4, could become IPv6 if CPE one day supports sub-DHCPv6-PD) subnets right there. (If you’ve ever wondered why most ADSL modem/routers default to 192.168.1.0/24, and most non-ADSL routers default to 192.168.2.0/24, this is the precise use case in mind.) I’m a power user, and have used 5 × /64’s out of my /56 at various stages. So a /60 would do me nicely, but I can think of a couple of my own clients who are approaching 16 separate subnets. A /56 would be needed for them. It’s easier to estimate IP allocation growth when you have to deal with x number of customers, rather than needing to separately deal with business/residential trends if you are delegating different sized subnets to each demographic. In other words, it’s much easier to just give a /56 to everyone. You’ve gotta pick your battles. Squeezing 100% efficiency out of your IP allocations isn’t one I want to fight.