Re: IPv6 prefix lengths - how long?

[James R Cutler <[e-mail]>]

> On Jun 8, 2019, at 12:28 PM, Philip Homburg <[e-mail]> wrote:
> 
>> The RFC 4291 IPv6 addressing and the original stance on 64bit boundary was bas
>> ed on the EUI64 format for the Mac generated FFFE bit stiff between the 3rd an
>> d 4th octet of the station id or random station id.
>> 
>> I agree that a 64bit station id was overkill and was made 20 years ago thinkin
>> g futuristically that every physical device you can think of would have an IP 
>> but now in reality large in my opinion that would never be used and really was
>> ted valuable bits on a station Id that could have been used more wisely to exp
>> and the prefix length.
> 
> With SLAAC, EUI64 has to some extent been replaced with pseudo-random 
> numbers.
> 
> For that to work, the number of bits needs to be sufficient to avoid
> collisions. The exact number of bits you need depends on the number of
> addresses on a subnet and how much you care about the damage done by
> collisions.
> 
> The problem is that we know that a 64 bit pseudo-random number is safe,
> but there is no sensible way to set a lower bound. There certainly is
> no consensus on a lower bound.
> 
> At the same time, we are not running out /64 prefixes. We have prefix
> allocation problem. We have enough /64s to give every virtual subnet its
> own /64.
> 
> So the obvious thing to do is to leave the 64 bit boundary in place for SLAAC.
> 
> If you really need longer prefixes, then just use static configuration or
> DHCPv6.
> 
> 
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I have difficulty considering the use of a 64 bit as a “waste" because it:
1. Has not been shown to create a resource shortage in the foreseeable future.
2. It is a “safe” size for a pseudo-random space as far as we know.
3. As Philip Homburg stated, we have no proof for a minimum size space.

I consider the effort and confusion involved in modification away from 64 bit Station IDs to be a waste (SLAAC, anyone?). 

I would rather see the effort put into better solutions security problems, including name to address resolution and routing.