(no email)
Date: Thu Jan 03 2008 - 06:06:52 EST
> So if /64 is "subnet" rather than "node" then the practice of
> placing one and only one node per subnet is pretty wasteful.
In an IPv6 network, a /64 is the subnet prefix of a single
broadcast domain, i.e. a single unbridged Ethernet segment.
Within this subnet, there are many /128s which represent
interfaces connected to the broadcast domain. These /128's
are not "nodes" in the common sense of the term, i.e. they
are not "boxes" or "devices". In some case, a device will
only have a single interface connected to the broadcast
domain, but ot could have more than one. If the device
is a virtualization host, as is increasingly common, then
it will have many virtual interfaces connected to the
broadcast domain, each of which will have a /128 assigned
to it.
> And giving residential users a /48 will leave them with 80
> bits for addressing.
No, it gives them 16 bits for subnetting. Everybody gets
64 bits for addressing because everybody (except oddballs
and enevelope pushers) uses a /64 subnet size. Since 64
bits are more than anyone could ever possibly need for
addressing and 16 bits is more than an end site could ever
possibly need for subnetting, the /48 is an ideal allocation
size. The whole point of IPv6 is to get rid of scarcity
and parsimony in network architecture. If you aren't giving
people more addresses than they need, then you aren't
following the fundamental IPv6 model.
Note that it is NOT wasteful to give people more addresses
than they need. It allows things like the ULA random subnet
selection algorithm to function with minimal probability of
collision.
> 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.
Yes! In IPv6 we do not allocate addresses, we allocate subnet
bits. We don't count addresses either, we use an HD ratio based
on counting subnets. People don't "get addresses" or "have addresses".
They get subnets and have subnets.
> So Acme DSL has been given a /32 from ARIN.
> Take someone like Comcast with ~12 million subscribers.
Can anybody say "scaling effects"? Comcast will never do things
like a small ISP and vice versa.
> 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.
Bad calculation. IPv6 usage efficiency is measured using the
HD ratio and that is not what you are calculating. This is
an especially important point for mid-size ISPs who go for
a /32 allocation from ARIN. If you use up that /32 allocation
and go back to ARIN to request another /32, you will *NOT* be
able to bamboozle them with arbitrary figures like you are
throwing around here. You *WILL* need to demonstrate that you
meet the current HD ratio guidelines to justify another block.
> 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 would be good to seem some mid-sized ISPs presenting how
they designed their internal addressing architecture taking
into account the HD ratio needed to justify an additional
allocation. This would include how they handle BGP route
aggregation internally and externally.
--Michael Dillon
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