RFC 791 / RFC 8200Lane A · FoundationsFREE

IPv4 vs IPv6

IPv4 addresses are 32 bits; IPv6 are 128 bits — 4× wider. The animation runs both side-by-side: top track is v4, bottom is v6. The v6 chip renders visibly larger to make the address-space difference legible without doing the math.

Animation

Engineering pitfalls

Dual-stack deployment misconfiguration

Hosts that prefer v6 will silently fall back to v4 if v6 fails — masking real connectivity issues. Disable Happy Eyeballs during diagnostic sessions to see the truth.

NAT64 / DNS64 corner cases

Translating between v4 and v6 fails on IP literals embedded in payloads (FTP, SIP). Use Application-Layer Gateways or migrate the application.

ULA (fc00::/7) vs GUA — don't confuse them

Unique Local Addresses are private, like RFC 1918 v4 ranges. Routing ULA across the public Internet won't work — the prefix is non-routable by design.

References

Primary sources
  • RFC 791 — Internet Protocol (IPv4).
  • RFC 8200 — Internet Protocol, Version 6 (IPv6) Specification.
  • RFC 6724 — Default Address Selection for Internet Protocol Version 6.