From: Donald Stahl (no email)
Date: Thu Jan 03 2008 - 09:19:17 EST
> So if /64 is "subnet" rather than "node" then the practice of placing one
> and only one node per subnet is pretty wasteful.
The whole point here is flexibility. IEEE defined several standards for
globally unique identifiers including EUI-48/MAC-48 and EUI-64.
MAC-48 should last us til 2100, but the IEEE seems to be thinking longer
term and also came out with EUI-64. Rather than create a protocol that
wouldn't be able to handle longer MAC addresses the IPv6 WG decided to use
EUI-64 for the host address in IPv6. This works for two reasons, a) There
is a defined method for converting from MAC-48 to EUI-64 addresses (and
back) and b) Even if Ethernet (or whatever comes next) uses a longer MAC
addresses (up to 64 bits obviously) it will still make sense in IPv6.
64 bits is also a nice multiple for 32 and 64 bit systems which doesn't
hurt when you're writing routing software or designing hardware.
> And giving residential users a /48 will leave them with 80 bits for
> addressing.
It leaves them with 65k subnets to choose from. Would a /56 make more
sense? Right now- sure- becaue we lack the imagination to really guess
what might happen in the future. Nanobots each with their own address, IP
connected everything, who knows? Assigning a /48 to everyone gives
everyone ample room and simplifies provisioning.
I'd rather push for /48 and have people settle on /56 than push for /56
and have people settle on /64.
> 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.
In answer- so what?
> So in short, a /48 to subscribers seems like complete overkill, and a /32 to
> ISP's seems completely inadequate (80 vs 16 bits).
A /32 is the equivalent of a class A. How many small ISP's do you know
with a class A? And larger networks? Give Comcast a /18. There is plenty
of space.
IPv4 is 32 bits and has room for 4 billion addresses.
Adding one additional bit gives you 33 bits and room for 8 billion
addresses. Adding two additional bits gives you room for 16 billion.
Adding 32 additional bits gives you room for 4 billion times 4 billion
addresses. Seriously- stop and think about that for a second. We've
taken the entire IPv4 Internet, multiplied it by 4 billion, and set
that aside JUST FOR THE NETWORK PORTION of addresses! We've got 4 billion
times 4 billion networks- that's a mind numbing increase in size even if
you only assign a single host to each /64 subnet. If you put multiple
hosts on each subnet then you've got an even larger space.
People just can't seem to wrap their head around how large the new
address space is.
-Don
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