What was the main motivation for designing IPv6 in the first place?

IPv4's 32-bit address space (~4.3 billion addresses) ran out, and IPv6's 128 bits make addresses effectively unlimited again.

IPv4 is over 40 years old and was designed for a handful of research computers — not billions of smartphones, IoT devices, and servers.

The core driver — address exhaustion:

• IPv4 = 32 bits = 4,294,967,296 addresses (already fewer than humans on Earth)
• The IANA central pool of free IPv4 blocks was exhausted in 2011; the regional registries followed soon after
• Stop-gaps like NAT (sharing one public IP among many private hosts) kept IPv4 alive but broke the "every device is directly reachable" end-to-end model

IPv6's answer — 128 bits:

• 2¹²⁸ ≈ 340 undecillion (340 × 10³⁶) addresses
• Enough to give every grain of sand on Earth its own address many times over — so NAT becomes unnecessary

Tip: Remember the jump as "32 → 128 bits" — that's 4× the bits, but because it's exponential, it's an astronomically larger space, not 4× larger.

Go deeper:

• IPv4 address exhaustion (Wikipedia) — the 2011 IANA pool depletion, per-RIR dates, and NAT as the stop-gap that drove IPv6.
• IPv6 (Wikipedia) — why the IETF built IPv6 and how 128-bit addressing answers exhaustion.