On Sun, Aug 7, 2011 at 6:09 PM, Jonathon Exley <Jonathon.Exley@kordia.co.nz> wrote:
This has probably been said before, but it makes me uncomfortable to think of everybody in the world being given /48 subnets by default. All of a sudden that wide expanse of 2^128 IP addresses shrinks to 2^48 sites. Sure that's still 65535 times more than 2^32 IPv4 addresses, but wouldn't it be wise to apply some conservatism now to allow the IPv6 address space to last for many more years? After all, there are only 4 bits of IP version field so the basic packet format won't last forever.
Hi Jonathan, IPv6 uses a slightly different mental model when it comes to address allocation. In IPv4 you assigned blocks of 32-bit addresses. In IPv6 this is no longer the case. You do not assign blocks of 128-bit addresses. In IPv6 you assign blocks of 64-bit LANs. Each LAN is 64-bits long as required by technologies like SLAAC. So, a /48 is 65k LANs, _not_ however many bazillion addresses. The question you should be asking is: is it excessive or unwise to go around assigning 65,000 LANs to every customer? Would 256 (/56) or 1 (/64) be a better number? Assigning 1 LAN seems questionable. We're trying to avoid NAT with IPv6 which means a customer may want to spend a LAN on things like the interior network of a virtual machine server. It's hard to do this if you only have one LAN. On the other hand, a whole lot of folks have through this through before you and concluded that a /56 (256 LANs per customer) is a smarter starting point than a /48. Regards, Bill Herrin -- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004