How Was IPv6 Address Size Chosen?

• some wanted fixed-length, 64-bit addresses

  • easily good for 1012 sites, 1015 nodes, at .0001 allocation efficiency (3 orders of mag. more than IPng requirement)
  • minimizes growth of per-packet header overhead
  • efficient for software processing

• some wanted variable-length, up to 160 bits

  • compatible with OSI NSAP addressing plans
  • big enough for auto-configuration using IEEE 802 addresses
  • could start with addresses shorter than 64 bits & grow later

• settled on fixed-length, 128-bit addresses

  • (340,282,366,920,938,463,463,374,607,431,768,211,456 in all!)

Notes: