Re: Extending a /64 (ATN/IPS worked example)

[Brian E Carpenter <[e-mail]>]

On 18-Nov-20 04:55, Philip Homburg wrote:
> In your letter dated Tue, 17 Nov 2020 15:02:40 +0000 you wrote:
>>> This a clear example of a bad addressing plan. If you have 5000 airlines and
>>> the biggest has 1300 aircraft then you don't give all tiny airlines the
>>> same amount of space you need for the biggest.
>>>
>> It's only a "bad addressing plan" if your sole success criteria is dense 
>> allocation. IPv6 should have liberated us from such a narrow success 
>> criteria. The success criteria that I am invoking include cost of 
>> administration and legacy support.
> 
> 'should have' is an interesting concept. We can't really go back in time.

To be clear, the IPv6 *fixed length* address model changes the parameters
of allocation practice because of moving from (say) 24 to (say) 64 bits
of routeable prefix, but in no way changes the philosophy of allocation
practice. IPv6 has ~64 topology bits instead of ~24; the actual numbers
in the H-ratio calculation change; the potential lifetime of the address
space expands enormously; the economic value of address space collapse
enormously. But all of that breaks if you start assigning address bits
non-topologically. That's why IPv6 and IPv4 share CIDR as the basis
for both prefix allocation and wide-area routing.

To get away from that, we'd indeed have to jump into our time machines,
go back to a meeting that happened just outside O'Hare airport in early
1994, and agree on a variable length addressing scheme.

> Technically we can just do a complete overhaul of the IPv6 addressing 
> architecture. But I doubt that people who now have existing IPv6 networks and
> products would be interested in that. Changing a widely adopted
> architecture also has a huge cost.
> 
>> I also do not see the point in having a different (shorter) prefix 
>> length for aircraft in smaller airlines compared with those in larger 
>> airlines.
> 
> Well, ISPs with few customers have a longer prefix than those with many
> customers. I guess you propose that we should have taken the shortest
> prefix needed for the largest ISP in the world, and then give the same
> prefix to every last tiny ISP as well?

Exactly. An operator of any kind should get a prefix that matches their
current and projected requirements. That's what CIDR-based allocation
is all about. Airlines are no different.

   Brian

> 
>> If you are arguing for dense allocation as a general rule then this 
>> should apply to the whole /64 prefix. I assume that you are demanding 
>> that ISPs allocate a /64 to all their users unless they can make the 
>> case for multiple subnets and, even then, are parsimonious in their 
>> attitude and push back hard against any user that wants more than a /60, 
>> demanding proof that they have more than 256 subnets.
> 
> You can make that argument, but is not part of the design of IPv6. The
> design of IPv6 is the endusers should always have enough space to number
> their networks.
> 
> 
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