How Big is 128 Bits of Address Space?

• Very, very big

• 2128 = 340,282,366,920,938,463,463,374,607,431,768,211,456

• Another way of thinking about it

• • Every square Angstrom on the surface of the Earth could be assigned over 4000 unique IPv6 addresses
  • • 1 Angstrom = 1/10 nanometer

• Why 128 bits?

• • A number of people maintain that with sane rationing, 64 bits would be more than enough
  • Others argued that any fixed address format would eventually be exhausted
  • 128 was a compromise