nanog mailing list archives
Re: Assigning IPv6 /48's to CPE's?
From: Donald Stahl <don () calis blacksun org>
Date: Thu, 3 Jan 2008 09:19:17 -0500 (EST)
The whole point here is flexibility. IEEE defined several standards for globally unique identifiers including EUI-48/MAC-48 and EUI-64.So if /64 is "subnet" rather than "node" then the practice of placing one and only one node per subnet is pretty wasteful.
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.
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.And giving residential users a /48 will leave them with 80 bits for addressing.
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?
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.So in short, a /48 to subscribers seems like complete overkill, and a /32 to ISP's seems completely inadequate (80 vs 16 bits).
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
Current thread:
- Re: Assigning IPv6 /48's to CPE's?, (continued)
- Re: Assigning IPv6 /48's to CPE's? Mikael Abrahamsson (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Rick Astley (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Randy Bush (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Rick Astley (Jan 03)
- RE: Assigning IPv6 /48's to CPE's? michael.dillon (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? sthaug (Jan 03)
- RE: Assigning IPv6 /48's to CPE's? michael.dillon (Jan 03)
- RE: Assigning IPv6 /48's to CPE's? Donald Stahl (Jan 03)
- RE: Assigning IPv6 /48's to CPE's? michael.dillon (Jan 03)
- RE: Assigning IPv6 /48's to CPE's? Donald Stahl (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Donald Stahl (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Chris Adams (Jan 03)
- RE: Assigning IPv6 /48's to CPE's? michael.dillon (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Mark Andrews (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Donald Stahl (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? William Herrin (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Tim Franklin (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? William Herrin (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Mark Smith (Jan 04)
- Re: Assigning IPv6 /48's to CPE's? Vinny Abello (Jan 03)
- Re: Assigning IPv6 /48's to CPE's? Valdis . Kletnieks (Jan 03)