IPv4 ran out a decade ago, the only reason why it continues to work at all is because of two things:
- Compatibility bridges for v6-only hosts to connect to v4 servers
- The IP address market encouraging old v4 allocation owners to sell off their space (at the expense of a bloated routing table)
In 2009, IANA and the RIRs created a process for buying and selling IP addresses. Which is something they never wanted to allow, but their hand was forced by the abysmal levels of v6 adoption back then. Two years later IANA would allocate the last /8s, and the RIRs that got those allocations would exhaust them in the years following[1]. The only virgin v4 address space remaining is reserved specifically for ISPs setting up v4 compatibility for native v6 networks.
You did not notice this because the v6 transition has already happened, and it was boring. In 2023, Google reports 40-45% v6 adoption[0]. This is largely due to LTE making v6 a mandatory feature. Had we kept mobile traffic on v4, networks would've adopted shedloads of CGNAT, and even then that hits a wall when you start running out of ephemeral ports to disguise addressing information inside of. This would have resulted in significantly worse behavior for smartphone users, especially in heavily populated countries like India (which have far higher v6 utilization).
- Compatibility bridges for v6-only hosts to connect to v4 servers
- The IP address market encouraging old v4 allocation owners to sell off their space (at the expense of a bloated routing table)
In 2009, IANA and the RIRs created a process for buying and selling IP addresses. Which is something they never wanted to allow, but their hand was forced by the abysmal levels of v6 adoption back then. Two years later IANA would allocate the last /8s, and the RIRs that got those allocations would exhaust them in the years following[1]. The only virgin v4 address space remaining is reserved specifically for ISPs setting up v4 compatibility for native v6 networks.
You did not notice this because the v6 transition has already happened, and it was boring. In 2023, Google reports 40-45% v6 adoption[0]. This is largely due to LTE making v6 a mandatory feature. Had we kept mobile traffic on v4, networks would've adopted shedloads of CGNAT, and even then that hits a wall when you start running out of ephemeral ports to disguise addressing information inside of. This would have resulted in significantly worse behavior for smartphone users, especially in heavily populated countries like India (which have far higher v6 utilization).
[0] https://www.google.com/intl/en/ipv6/statistics.html#tab=ipv6...
[1] https://en.wikipedia.org/wiki/IPv4_address_exhaustion