Do you seek information on how to plan subnetting or on more technical issues like how to dual stack your network? In the later case, you would need to tell more about your network. Eg. if you have a MPLS network (like we do) and you have your internet in a L3VPN enabling IPv6 is really easy and has almost no impact on the network. As an alternative to the plan that Owen describes, I can offer the way we did it: Our IPv6 address plan is tied to our IPv4 addressing, such that there is a mapping from IPv4 address to IPv6 /48 prefix. That way we do not need to allocate IPv6 as such. The mapping is a database with IPv4 /24 as key and IPv6 /40 as value. Example: 85.204.120.0/24 maps to 2a00:7660:500::/40. Take the user with the IPv4 address 85.204.120.12. This address maps to 2a00:7660:50b::/48. Note that 12 is "0b" in hexadecimal. We are an eyeball network where most users have only one single IPv4 address. We assign the IPv4 addresses statically (never changes). A few users bought extra IPv4 address and that creates a hole in our address plan, but we do not care. Officially the extra /48 is not assigned to the user, because that would be against the rules. Our address plan creates a very efficient allocation scheme, that is not strictly needed as you have the more loose ARIN rules (we are in RIPE). Regards, Baldur