How big is IPv6?

IPv6 uses 128-bit addressing allowing 2¹²⁸ addresses.

Analogy 1: Size based analogy
Say 1 IP address is equivalent to 1 picometer ( 10^-12 meter = 0.000000000001 meter )
IPv4 is the size of an ant:  2³² picometer = 4.29mm  
IPv6 is ridiculously large: (2¹²⁸) picometers = 35 Billion light years
Note: 1 light year = 9.4605284 × 10¹² kilometers = 5.87849981 × 10¹² miles

Analogy 2: Weight based analogy

Say 1 speck of dust weighs 1 microgram
Mass of the Earth = 5.98 x 10²⁷ grams = 5.98 x 10³³ microgram
(Ref: http://en.wikipedia.org/wiki/Earth_mass)

Say Earth is made up of the dust particles

Total amount of the dust particles in Earth = 5.98 x 10³³ which is equivalent to 2¹¹²

Total number of IPv6 Addresses: 2¹²⁸

IPv6 address space is good enough to assign an IP address to each dust particles in  2^(128-112)=2¹⁶= 65536 planets the size of the earth.

Conclusion:

IPv6 address space allocation looks wasteful but it is so beautiful that you don't have to worry about conserving IP addresses any more as you can get ridiculously huge amount of address space. Now you can focus more on managing network rather than managing network address space itself. With that being said, proper IPv6 address planning is crucial otherwise it can get ugly and become a nightmare.

Wise principle to follow while doing IPv6 Address planning: Forget about IPv4 thinking, like address conservation, subnets, legacy class concepts, subnet masks (simply remember how to use CIDR style notation), etc. 

IPv6 is 128 bits. Make life simple. Break it into two 64 bits. First 64 bits for network and second 64 bits for interface.You can break first 64 network bits into Global Unicast Prefix(48 bits) and Subnet(64 minus 48 = 16 bits).


More yet to come...