Using /126 for IPv6 router links

Mon Jan 25 10:45:01 UTC 2010

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. :)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)