Re: Backwards compatible
>People already moan constantly about how "complicated" v6 is, despite v6 using the same addressing and routing model as v4.
But it doesn't quite use the same model, remember it is more prescriptive about how the first 64 bits are divided up eg. Registry : ISP Prefix : Site Prefix : LAN Prefix
Although I suppose this is in line with the original specification of IPv4 when subnetting hadn't been considered. [Subnetting only being officially recognised in 1985 - RFC950.]