Good Morning! > -----Original Message----- > From: Richard A Steenbergen [mailto:r...@e-gerbil.net] > Sent: Monday, January 25, 2010 05:45 > To: Andy Davidson > Cc: nanog@nanog.org > Subject: Re: Using /126 for IPv6 router links > > On Mon, Jan 25, 2010 at 09:12:49AM +0000, Andy Davidson wrote: > > There are 4,294,967,296 /64s in my own /32 allocation. If we only ever > > use 2000::/3 on the internet, I make that 2,305,843,009,213,693,952 > > /64s. This is enough to fill over seven Lake Eries. The total amount > > of ipv6 address space is exponentially larger still - I have just looked > > at 2000::/3 in these maths. > > > > THE IPv6 ADDRESS SPACE IS VERY, VERY, VERY BIG. > > Don't get carried away with all of that "IPv6 is huge" math, it quickly > deteriorates when you start digging into it. Auto-configuration reduces > it from 340282366920938463463374607431768211456 to 18446744073709551616 > (that's 0.000000000000000005% of the original 128 bit space). Now as an > end user you might get anything ranging from a /56 to a /64, that's only > between 1 - 256 IPs, barely a significant increase at all if you were to > actually use a /64 for each routed IP rather than as each routed subnet. > As a small network you might get a /48, so that even if you gave out > /64s to everyone it would be only 16 bits of space for you (the > equivalent of getting a class B back in IPv4 land), something like a > 8-16 bit improvement over what a similar sized network would have gotten > in IPv4. As a bigger ISP you might get a /32, but it's the same thing, > only 16 bits of space when you have to give out /48s. All we've really > done is buy ourselves an 8 to 16 bit improvement at every level of > allocation space (and a lot of prefix bloat for when we start using more > than 2000::/3), which is a FAR cry from the 2^128 "omg big number, we > can give every molecule an IPv6 address" math of the popular > imagination. :)
While I agree with parts of what you are saying - that using the "simple 2^128" math can be misleading, let's be clear on a few things: *) 2^61 is still very, very big. That is the number of IPv6 network segments available within 2000::/3. *) An end-user should get something between a /48 and a /56, _maybe_ as low as a /60 ... hopefully never a /64. Really. **) Let's call the /48s enterprise assignments, and the /56s home assignments ... ? **) And your /56 to /64 is NOT 1-256 IPs, it is 1-256 segments. **) And, using the expected /48-/56, the numbers are really 256-64k subnets. **) Each segment supporting as many hosts as you want it to. Probably nowhere near 2^64, but that isn't the point :). *) _Any_ ISP gets a /32 by default, a "bigger ISP" can readily get more. So, actually, we have 'bought' ourselves much more space. *) The standard registry allocation is a /12. So within the /3 we have 512 of those. Note: We currently have 5 RIRs. *) A /12 yields 20 bits of /32s. So within any given /12, we have ~1M ISPs. *) The "standard ISP /32" can support 64K Enterprises or 16.7M Homes. **) Oh, and if you need more = just ask. *) Even allowing for inefficiency / room to grow / summarization - I think we are good for quite some time. *) And this is just the first /3. Note: "All we've really done is buy ourselves an 8 to 16 bit improvement at every level of allocation space" *) And you don't think 8-16 bits _AT EVERY LEVEL_ is a bit deal?? **) Remembering that the original address space was 'only' 32bits. **) I guess only supporting 256-64k more registries, each of which can support 256-64k more ISPs, each of which can support 256-64k more customers just isn't that useful to you? *) Additionally - the number of IPs per segment, which is not the same as the number of hosts per segment, is much vaster. The quite common IPv4 /24 being analogous to an IPv6 /64 ... /TJ PS - We also get much more multicast space, Which Is Nice(TM).