Using /126 for IPv6 router links

Larry Sheldon LarrySheldon at
Mon Jan 25 18:50:14 UTC 2010

On 1/25/2010 4:45 AM, Richard A Steenbergen wrote:
> 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.
> 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. :)

And it does not account for the factor that I was trying to shine a 
light on--the it-is-infinitely-huge is at risk of failing due to 
inventions we can not conceive of.

Who knew, in the 1940's that every person would be assigned as many as 
five or more telephone numbers  (exaggeration?  In this house, occupied 
by two people there are 4 addressable PSTN devices, only one of which 
leaves the house if one of us does, and there are 6 devices that share 
an address but could easily have individual addresses, and would if we 
were using one of the VOIP services).

Who knew in the 1980's that refrigerator's would need IP addresses?  (We 
should not have been surprised, Coke machines did.)

And for all the concern about IPv4 exhaustion, what would have happened 
if the people who fought fiercely against RFC 1918 had won the day?

Yes the numbers in IPv6 are huge, no doubt about it.

But I say, to say "impossible to exhaust" is a fools errand.  Somebody 
will find a way to exhaust the pool, just to be contrary, if for no 
currently recognized "legitimate" reason.

"Government big enough to supply everything you need is big enough to 
take everything you have."

Remember:  The Ark was built by amateurs, the Titanic by professionals.

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