On Dec 28, 2017, at 14:31, Thomas Bellman <bellman@nsc.liu.se> wrote:
On 2017-12-28 22:31, Owen DeLong wrote:
Sure, but that’s intended in the design of IPv6. There’s really no need to think beyond 2^64 because the intent is that a /64 is a single subnet no matter how many or how few machines you want to put on it.
Before anyone rolls out the argument about the waste of a /64 for a point to point link with two hosts on it, please consider that the relative difference in waste between a /64 with 10,000 hosts on it and a /64 with 2 hosts on it is less than the rounding error in claiming that a /64 is roughly 18 quintillion addresses. In fact, it’s orders of magnitude less.
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We may, someday, wish we had gone to some value of N larger than 128, but I seriously doubt it will occur in my lifetime.
My problem with the IPv6 addressing scheme is not the waste of 64 bits for the interface identifier, but the lack of bits for the subnet id. 16 bits (as you normally get a /48) is not much for a semi-large organi- zation, and will force many to have a dense address plan, handing out just one or a few subnets at a time, resulting in a patch-work of allocations. 24 bits for subnet id would be more usable.
That’s absurd. The intent is a /48 per end SITE. Not per organization. According to ARIN policies, the definition of an end site is a single building or structure or a single tenant within a multi-tenant building or structure. With nibble boundary round-up in policy, an organization with more than one site can get at least 16 /48s. Further, a university could (technically) get a /48 for every dorm room.
Consider e.g. a university or company campus. There are probably at least 16 departments, so I would like to use 8 bits as department id. Several departments are likely to have offices on more than one floor, or in more than one building, so I would like to let them have 4 bits to specify location, and then 8 bits to specify office/workplace within each location. And allow them to hand out 16 subnets per workplace. That adds up to 24 bits. So a /40 would be nice, not a /48.
A campus is, by definition multiple end sites.
Similarly, an ISP that wants a structured address plan, e.g. to encode prefecture, city and part of city in the address, will quickly use up bits in the customer id part of the address.
An ISP can qualify for up to a /12 in a single allocation. They get two levels of hierarchy at which they can aggregate and do a nibble-boundary round-up. As such, I’m not sure how many bits you want for that that you feel you can’t have. Remember, /32 is just the default no questions asked minimum v6 isp allocation. Not the maximum. I know of at least three isps that have /24s or more of ipv6 space.
/Bellman
Owen