[Mxsmanic]

Anahata writes:

I haven't yet read a reasoned critique of IPV6's allocation scheme, but I
have a suspicion that the plan behind increasing IP address lengths by a
factor of 4 instead of (as you might expect) 2 was to make sure they
couldn't run out in any foreseeable length of time. 128 bits is a lot of
addresses, however you cut the cake.

They can easily run out. The problem is that engineers think in linear terms
when looking at address spaces, but the results are exponential.

For example, the 128-bit IPv6 address has already been divided into two 64-bit
fields for some purposes. Intuitively, the people doing this "feel" as if the
address space has been reduced by half, but it hasn't. It has been reduced by
more than 99.99999999999999999%. Continued allocation of fields within the
128-bit address will continue to reduce the address space exponentially until
there is nothing left. That's exactly the same mistake that was made with
32-bit addresses.

Engineers and others often forget that a linear reduction in address size is
an exponential reduction in address space. Encoding information into the
address itself dramatically restricts the number of addresses available.

I've seen software engineers exhaust huge virtual address spaces in the same
way. Often engineers think that an address space of n bits equates to
"infinite" and allocate virtual space serially and generously, and are then
surprised when systems crash because they've run out of address space.

Note that even Ethernet addresses (so called 'MAC' addresses) have had a
good run. Every piece of Ethernet kit ever made has a world-wide unique
address, with manufacturers allocated blocks by IEEE, and I haven't heard
any rumours they are likely to run out soon, and they are 'only' 48 bits.

The 48-bit addresses are expected to last until 2100 by the IEEE. This sounds
generous until you realize that a 48-bit address space assigned serially would
accommodate 281,474,976,710,656 Ethernet cards. The address space has been
severely (exponentially) reduced by linear allocation of address bits.