What are the three major limitations of IPv4?

Question

Accepted Answer

Address depletion (~4.3 billion is too few), loss of end-to-end connectivity (caused by private addressing/NAT), and increased network complexity (NAT side effects).
IPv4 has three major limitations:

Limitation
Description

IPv4 address depletion
We have basically run out of IPv4 addresses (only ~4.3 billion total)

Lack of end-to-end connectivity
Private addressing and NAT were created to extend IPv4's life, but this ended direct host-to-host communication

Increased network complexity
NAT was meant as a temporary solution but creates latency and troubleshooting issues

Context: These limitations drove the development of IPv6. The Regional Internet Registries (RIRs) have exhausted their IPv4 address pools:

APNIC (Asia-Pacific) exhausted in 2011
RIPE NCC (Europe) exhausted in 2012
LACNIC (Latin America) exhausted in 2014
ARIN (North America) exhausted in 2015

Go deeper:

Wikipedia — IPv4 address exhaustion — the depletion timeline, RIR dates, and mitigation history.
 Wikipedia — IPv4 — the 32-bit address space limit and why NAT was needed.

Limitation	Description
IPv4 address depletion	We have basically run out of IPv4 addresses (only ~4.3 billion total)
Lack of end-to-end connectivity	Private addressing and NAT were created to extend IPv4's life, but this ended direct host-to-host communication
Increased network complexity	NAT was meant as a temporary solution but creates latency and troubleshooting issues