Waste will kill ipv6 too

Owen DeLong owen at delong.com
Fri Dec 29 01:23:29 CST 2017


> On Dec 28, 2017, at 14:31, Thomas Bellman <bellman at 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.
> 
> [...]
> 
>> 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




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