Reclaiming IPv4 Class E's 240.0.0.0/4

Original Article ↗ Hacker News Discussion ↗

Thread focus

  • Debate centers on whether reclaiming IPv4 Class E (240.0.0.0/4) is worthwhile versus pushing harder on IPv6.
  • Many see 240/4 as a distraction that prolongs IPv4 dependence without solving structural problems.

IPv6 vs reclaiming 240/4

  • Pro-IPv6 view: reclaiming 240/4 breaks devices, firewalls, and software, buys only a few years, and weakens incentives to deploy IPv6.
  • Critics of 240/4 note that to use it on the public Internet you effectively need near‑100% support across OSes, routers, and middleboxes; anything less creates opaque reachability bugs.
  • Some argue 240/4 might be useful as extra private space (e.g., behind NAT, containers) but not as globally routable space.

IPv6 design, complexity, and backward‑compatibility debates

  • Several commenters argue IPv6 could have been a “bigger IPv4” with minimal changes (longer addresses, same model), citing historical proposals (TP/IX, TUBA, Extended IP).
  • Counter-argument: any expanded-address protocol would still break APIs, hardware, and assumptions; you’d still need new structs, DNS record types, and transition mechanisms.
  • IPv6-specific complaints: SLAAC and privacy addresses, multiple addresses per interface, dependence on ICMP, dynamic prefixes from ISPs, DHCPv6 vs SLAAC tensions, Android not supporting stateful DHCPv6.

Operational experiences and deployment barriers

  • Some report IPv6 has “just worked” for a decade (home ISPs, HE tunnels, mobile networks).
  • Others see IPv6 as flaky or absent (certain ISPs, cloud services, major sites like Github), making IPv6-only setups impractical.
  • Admins dislike dual-stack: two firewall configs, two address plans, more debugging surface, while IPv4 must remain anyway.
  • Usability gripe: IPv6 text form is hard to type, recognize, and select; tools and conventions (ifconfig, 8.8.8.8) are IPv4-centric.

NAT, CGNAT, and address scarcity

  • Some want IPv6 to eliminate NAT; others note NAT and CGNAT remain due to legacy IPv4-only services and dynamic prefixes.
  • Mobile carriers often run IPv6-only plus NAT64/DNS64 for IPv4 sites; suggested as a model for ISPs.
  • Address scarcity is now monetized (e.g., cloud IPv4 charges); this may slowly push services toward IPv6, but big holders feel little pressure.

Other reserved ranges (0/8, 127/8)

  • Reusing 127/8 or 0/8 is seen as far riskier than 240/4 due to ubiquitous hardcoded loopback and “this host” assumptions and potential security issues.
  • Some niche use of expanded 127/8 for local aliases exists; shrinking it (e.g., to /16) would be extremely slow and fragile.

Policy / incentives

  • Some advocate mandates (FCC or governments requiring IPv6, even v6-only government sites) to break the stalemate.
  • Others argue against misusing CVEs or hard mandates; emphasize that economics and inertia, not protocol design quality alone, explain slow adoption.