Article · Wikipedia archive · Last revised Jun 8, 2026

IPv6-to-IPv6 Network Prefix Translation

IPv6-to-IPv6 Network Prefix Translation (NPTv6) is a specification for IPv6 to achieve address-independence at the network edge, similar to network address translation (NAT) in Internet Protocol version 4 (IPv4). It has fewer architectural problems than IPv4 NAT; for example, it is stateless, uses a 1:1 address mapping and preserves the reachability attributed to the end-to-end principle. However, because the new address is chosen in a way that leaves the checksum unchanged the interface identifier bits change and this may break applications that embed data in them. Additionally, split-horizon DNS may be required for use in a business environment.

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Jun 8, 2026
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Wikipedia ↗
IPv6-to-IPv6 Network Prefix Translation
Communication protocol
PurposeNetwork address translation
Introduction2011 (2011)
RFC(s)6296, 7157...

IPv6-to-IPv6 Network Prefix Translation (NPTv6) is a specification for IPv6 to achieve address-independence at the network edge, similar to network address translation (NAT) in Internet Protocol version 4 (IPv4). It has fewer architectural problems than IPv4 NAT; for example, it is stateless, uses a 1:1 address mapping and preserves the reachability attributed to the end-to-end principle. However, because the new address is chosen in a way that leaves the checksum unchanged (checksum-neutral mapping) the interface identifier bits change and this may break applications that embed data in them (such as IPsec). Additionally, split-horizon DNS may be required for use in a business environment.

NPTv6 multihoming example source ↗

NAT66

NAT66 was the name used in earlier drafts of the standard.1 There were some initial proposals to rename it,2 and a few years later the name NPTv6 was chosen.3 One of the early versions defined two modes of operation within NAT66: a Two-Way Algorithmic mapping and a Topology Hiding Option, the latter of which used a non-reversible address mapping that would've required additional state in the translator, either in the form of a dynamic table or a statically defined set of address mappings.4 It was soon removed, leaving the two-way mapping as the only mode of operation and making the specification fully stateless.

Current usage of the term (by vendors, in informal contexts, etc.) is unclear: sometimes it's still employed as a synonym for NPTv65 but often it refers to a generic implementation of stateful NAT678 (or even full NAPT910) on IPv6.

References

References

  1. Wasserman, Margaret; Baser, Fred (2008-10-27). IPv6-to-IPv6 Network Address Translation (NAT66). IETF. I-D draft-mrw-behave-nat66.
  2. Wasserman, Margaret; Baser, Fred (November 2008). "NAT66: IPv6-to-IPv6 NAT" (PDF). BEHAVE WG, IETF 73. Minneapolis. p. 17.
  3. Wasserman, Margaret; Baser, Fred (2010-12-09). IPv6-to-IPv6 Network Prefix Translation. IETF. sec. 10.4. I-D draft-mrw-nat66-01.
  4. Wasserman, Margaret (2008-10-27). "Topology Hiding Option". IPv6-to-IPv6 Network Address Translation (NAT66). IETF. sec. 5.1.2. I-D draft-mrw-behave-nat66-01.
  5. "Support - 02-NAT66 configuration- H3C". www.h3c.com. Retrieved 2025-09-12.
  6. Hogg, Scott (2021-12-28). "You Thought There Was No NAT for IPv6, But NAT Still Exists". Infoblox Blog. Retrieved 2025-09-12.
  7. Yuhan, Guo (2023-12-13). "What Is NAT66? Why Do We Need NAT66?". Huawei. Retrieved 2025-09-12.
  8. "NAT66 policy". Fortinet.
  9. "3 Ways to Ruin Your Future Network with IPv6 Unique Local Addresses (Part 1 of 2)". Infoblox Blog. 2016-02-27. Retrieved 2021-12-24.
  10. "NAT66: The good, the bad, the ugly". APNIC Blog. 2018-02-02. Retrieved 2025-09-12.
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