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Re: Assigning IPv6 /48's to CPE's?

  • From: Donald Stahl
  • Date: Thu Jan 03 09:24:56 2008 

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