[101417] in North American Network Operators' Group
RE: Assigning IPv6 /48's to CPE's?
daemon@ATHENA.MIT.EDU (Donald Stahl)
Thu Jan 3 10:41:13 2008
Date: Thu, 3 Jan 2008 10:35:09 -0500 (EST)
From: Donald Stahl <don@calis.blacksun.org>
To: michael.dillon@bt.com
Cc: nanog@merit.edu
In-Reply-To: <D03E4899F2FB3D4C8464E8C76B3B68B001AB7714@E03MVC4-UKBR.domain1.systemhost.net>
Errors-To: owner-nanog@merit.edu
>> That's 281,474,976,710,656 /48 customer networks. It's 16
>> million times the number of class C's in the current IPv4
>> Internet. Am I just not thinking large or long term enough?
>
> No, you are just counting wrong. When you are talking /48's
> you are talking "number of bits of of subnet hierarchy", not
> "pile of pebbles on the beach". If you read the ARIN IPv6 policy
> you will see that they don't count /48's like pebbles, instead
> they use something called the HD Ratio.
I'm fully aware of HD ratio thanks :)
My point was to give a rough approximation of the size difference here,
not to talk about the specific numbers.
> Basically, this recognizes that IP networks are not flat piles
> of pebbles, but have a hierarchical aggregation structure in
> them. At each level of aggregation, you have to do a fitting
> exercise, where you fit what you have into a power of two
> sized block. If you have 5 subnets that need to be aggregated
> into a single higher level subnet, then you must use 3 bits
> of your subnet hierarchy, even though those 3 bits could be
> used for as many as 8 subnets.
>
> This is not waste. It is a fact imposed by the structure of
> IPv6 (and IPv4) subnet addresses. In fact, when you "throw away"
> subnets (addresses) like that, you are actually following a
> prudent conservation policy. That's because this kind of bitwise
> network addressing is cheaper to implement in hardware and
> can be processed faster in hardware when doing things like
> FIB lookups. That conserves MONEY and TIME which are vastly
> more important to conserve than theoretical counting capacity
> of a bitstring.
I'm not sure what your point is here. I'm not remotely trying to argue
this.
You made a point about HD ratio-
80% HD with 48 bits of network address still gives us
300,000,000,000 /48 networks (unless my math is very wrong). Again, I'm
not sure how we're going to use that up in 50 or 100 years, but I'm sure
history will prove me a fool.
-Don
