From: Rick Astley (no email)
Date: Thu Jan 03 2008 - 03:52:00 EST
>* /32 for ISPs unless they can justify more
>* /48 for subscribers unless they can justify more
>* /64 when you know for certain that one and only one subnet will ever be
required
>* /128 when you know for certain you're dealing with a single device
>* Sparse allocation so whichever size you choose you can usually increase
it by simply changing the prefix length.
So if /64 is "subnet" rather than "node" then the practice of placing one
and only one node per subnet is pretty wasteful.
And giving residential users a /48 will leave them with 80 bits for
addressing.
Even if the household was using 1,000,000,000,000,000 IP addresses in their
home, this would mean that they are still not using 99.9999999% of the IP
addresses they have been allocated.
I know the reason for this is becasue they are allocated IP's based on
number of possible subnets, rather than total number of available IP's, so
it would be more fair to say they are allocated 65,536 subnets.
So Acme DSL has been given a /32 from ARIN. Bob their administrator promptly
decides it is a good idea to just give each customer a /48 becasue who knows
/what/ their needs may be.
This gives Acme Bob enough IP addresses for 2^(48-32) or 65,536 customers
assuming bob uses none of these IP addresses for his own equipment and has a
single homed network.
If Bob has a multihomed network, he can't just give one /48 to a customer in
NY and the next one to a customer in CA unless he wants to fill up Internet
routing tables with /48's, so he will have to assign large aggregate blocks
to each region.
Accommodating for this, Bob is unlikely to plan for more than 30%
utilization in any one region, with most being less and some aggregate
blocks withheld entirely for growth.
So lets say Acme DSL's IPv6 deployment places them in the ballpark of 10%
utilization (not bad considering end users are wasting
99.99999999999999999999%), this gives them enough blocks for only 6,500
customers.
Take someone like Comcast with ~12 million subscribers.
It would take an IPv6 /24 to get 16.7 million /48's (2^24). With a net
efficiency of 10% they are going to need to be allocated 120 million /48's.
It would take a /21 to give them 2^(48-21) = ~134 million /48's.
So in short, a /48 to subscribers seems like complete overkill, and a /32 to
ISP's seems completely inadequate (80 vs 16 bits).
I thought one of the goals of IPv6 was to assign ISP's huge blocks with low
utilization so they don't have push a bunch of individual prefixes out to
the worlds routing tables?
It seems to me while being extra super sure we meet goal 1 of making sure
NAT is gone for ever (and ever) we fail goal 2 of not allocating a bunch of
prefixes to ISP's that are too small.
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