The Road Not Taken: A World Where IPv4 Evolved

Original Article ↗ Hacker News Discussion ↗

IPv4x alternate-history idea

  • IPv4x keeps IPv4 headers and 32‑bit routing, but tucks extra 96 bits of address into the payload, flagged in the header.
  • Legacy routers forward on the 32‑bit part; IPv4x‑aware gear uses the full 128 bits.
  • Proponents in the thread like the idea that:
    • Adoption could be incremental at the edges.
    • There’s only “one network” and one firewall/ACL view, not two parallel stacks.
    • Existing IPv4 space and topology remain first‑class.

Critiques: “Not really better than IPv6”

  • Many argue IPv4x needs the same fundamental changes as IPv6:
    • New code in routers, OS stacks, and middleboxes to understand longer addresses.
    • New DNS record types and updated apps to query and store them.
    • Larger socket address structures and API changes.
  • Once you support both 32‑bit and extended addresses, you are effectively dual‑stack again.
  • Flat 128‑bit space and routing aggregation problems remain; IPv4x doesn’t fix scaling, just shifts it.

NAT, compatibility, and address space

  • Some say the “road actually taken” was NAT: IP+port ≈ 48 bits, multi‑layer NAT ≈ “IPv4x in practice,” requiring no protocol change.
  • Others note NAT is stateful, constrains ports, complicates hole‑punching and non‑TCP/UDP protocols, and doesn’t behave like true routing.
  • IPv4x would still need NAT/translation to reach IPv4‑only endpoints, much like NAT64/CLAT for IPv6.

IPv6 adoption and operational experience

  • Several comments state IPv6 is already significantly deployed: large fractions of major site traffic, v6‑only mobile cores with 464xlat, v6‑only IoT stacks.
  • Others report frequent real‑world breakage (timeouts, bad defaults, VPN or DNS quirks) and prefer disabling IPv6.
  • Debate whether slow uptake is mostly:
    • Human/admin reluctance and lack of perceived payoff, or
    • Genuine complexity and fragile transition tooling.

Fairness and governance

  • A major criticism of IPv4x: all new 96‑bit subspace would attach to existing IPv4 owners, cementing early‑Internet incumbents and disadvantaging latecomers.
  • IPv6 is seen by some as more equitable, because the expanded space was reallocated rather than inherited.

Alternative mechanisms and lessons

  • IPv4x is repeatedly compared to existing IPv6 mechanisms: 6to4, IPv4‑mapped IPv6, NAT64/DNS64, 464xlat, 6rd.
  • Some argue better, standardized “one‑stack with transparent translation” (v6‑only + robust 46/64 translation) in OSes and CPE early on would have accelerated IPv6 far more than an IPv4‑compatible redesign.